Physics · Textbook solutions
Moving Charges and Magnetism
Every solved example, exercise, and miscellaneous question, in the order the textbook teaches them. Plus every board question asked from this chapter. · 26 questions
Worked Examples
12 q
Solved Examples
Worked · 12
- Eg 4.1A straight wire of mass and length carries a current of . It is suspended in mid-air by a uniform horizontal magnetic field (Fig. 4.3). What is the magnitude of the magnetic field?
- Eg 4.2If the magnetic field is parallel to the positive -axis and the charged particle is moving along the positive -axis (Fig. 4.4), which way would the Lorentz force be for (a) an electron (negative charge), (b) a proton (positive charge).
- Eg 4.3What is the radius of the path of an electron (mass and charge ) moving at a speed of in a magnetic field of perpendicular to it? What is its frequency? Calculate its energy in keV. ().
- Eg 4.4An element is placed at the origin and carries a large current (Fig. 4.8). What is the magnetic field on the -axis at a distance of . .
- Eg 4.5A straight wire carrying a current of is bent into a semi-circular arc of radius as shown in Fig. 4.11(a). Consider the magnetic field at the centre of the arc. (a) What is the magnetic field due to the straight segments? (b) In what way the contribution to from the semicircle differs from that of a circular loop and in what way does it resemble? (c) Would your answer be different if the wire were bent into a semi-circular arc of the same radius but in the opposite way as shown in Fig. 4.11(b)?
- Eg 4.6Consider a tightly wound turn coil of radius , carrying a current of . What is the magnitude of the magnetic field at the centre of the coil?
- Eg 4.7Figure 4.13 shows a long straight wire of a circular cross-section (radius ) carrying steady current . The current is uniformly distributed across this cross-section. Calculate the magnetic field in the region and .
- Eg 4.8A solenoid of length has a radius of and is made up of turns. It carries a current of . What is the magnitude of the magnetic field inside the solenoid?
- Eg 4.9The horizontal component of the earth's magnetic field at a certain place is and the direction of the field is from the geographic south to the geographic north. A very long straight conductor is carrying a steady current of . What is the force per unit length on it when it is placed on a horizontal table and the direction of the current is (a) east to west; (b) south to north?
- Eg 4.10A turn closely wound circular coil of radius carries a current of . (a) What is the field at the centre of the coil? (b) What is the magnetic moment of this coil? The coil is placed in a vertical plane and is free to rotate about a horizontal axis which coincides with its diameter. A uniform magnetic field of in the horizontal direction exists such that initially the axis of the coil is in the direction of the field. The coil rotates through an angle of under the influence of the magnetic field. (c) What are the magnitudes of the torques on the coil in the initial and final position? (d) What is the angular speed acquired by the coil when it has rotated by ? The moment of inertia of the coil is .
- Eg 4.11(a) A current-carrying circular loop lies on a smooth horizontal plane. Can a uniform magnetic field be set up in such a manner that the loop turns around itself (i.e., turns about the vertical axis). (b) A current-carrying circular loop is located in a uniform external magnetic field. If the loop is free to turn, what is its orientation of stable equilibrium? Show that in this orientation, the flux of the total field (external field + field produced by the loop) is maximum. (c) A loop of irregular shape carrying current is located in an external magnetic field. If the wire is flexible, why does it change to a circular shape?
- Eg 4.12In the circuit (Fig. 4.23) the current is to be measured. What is the value of the current if the ammeter shown (a) is a galvanometer with a resistance ; (b) is a galvanometer described in (a) but converted to an ammeter by a shunt resistance ; (c) is an ideal ammeter with zero resistance? The circuit is a source in series with a resistor and the ammeter.
Exercises
14 q
- Ex 4.1A circular coil of wire consisting of turns, each of radius carries a current of . What is the magnitude of the magnetic field at the centre of the coil?
- Ex 4.2A long straight wire carries a current of . What is the magnitude of the field at a point from the wire?
- Ex 4.3A long straight wire in the horizontal plane carries a current of in north to south direction. Give the magnitude and direction of at a point east of the wire.
- Ex 4.4A horizontal overhead power line carries a current of in east to west direction. What is the magnitude and direction of the magnetic field due to the current below the line?
- Ex 4.5What is the magnitude of magnetic force per unit length on a wire carrying a current of and making an angle of with the direction of a uniform magnetic field of ?
- Ex 4.6A wire carrying a current of is placed inside a solenoid perpendicular to its axis. The magnetic field inside the solenoid is given to be . What is the magnetic force on the wire?
- Ex 4.7Two long and parallel straight wires A and B carrying currents of and in the same direction are separated by a distance of . Estimate the force on a section of wire A.
- Ex 4.8A closely wound solenoid long has layers of windings of turns each. The diameter of the solenoid is . If the current carried is , estimate the magnitude of inside the solenoid near its centre.
- Ex 4.9A square coil of side consists of turns and carries a current of . The coil is suspended vertically and the normal to the plane of the coil makes an angle of with the direction of a uniform horizontal magnetic field of magnitude . What is the magnitude of torque experienced by the coil?
- Ex 4.10Two moving coil meters, and have the following particulars: , , , , , , (The spring constants are identical for the two meters). Determine the ratio of (a) current sensitivity and (b) voltage sensitivity of and .
- Ex 4.11In a chamber, a uniform magnetic field of () is maintained. An electron is shot into the field with a speed of normal to the field. Explain why the path of the electron is a circle. Determine the radius of the circular orbit. (, )
- Ex 4.12In Exercise 4.11 obtain the frequency of revolution of the electron in its circular orbit. Does the answer depend on the speed of the electron? Explain.
- Ex 4.13(a)(a) A circular coil of turns and radius carrying a current of is suspended vertically in a uniform horizontal magnetic field of magnitude . The field lines make an angle of with the normal of the coil. Calculate the magnitude of the counter torque that must be applied to prevent the coil from turning.
- Ex 4.13(b)A circular coil of turns and radius carrying a current of is suspended vertically in a uniform horizontal magnetic field of magnitude , the field lines making an angle of with the normal of the coil, and a counter torque is applied to prevent the coil from turning. (b) Would your answer change, if the circular coil in (a) were replaced by a planar coil of some irregular shape that encloses the same area? (All other particulars are also unaltered.)
What the board has asked from this chapter
Questions per paper · 21 papers · 2023 to 2026
Bars average the full papers of each year. 47 further questions come from set variants and are listed below.
2023: 4.4 questions per paper. 2024: 5.2 questions per paper. 2025: 5.2 questions per paper. 2026: 4.6 questions per paper
2026
33 q
- 2Two particles of masses and having charges and respectively are projected with the same velocity in a region of uniform magnetic field pointing vertically upward. If they describe circular paths as shown in the figure, one may conclude that :
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Magnetic Force and Motion in a Magnetic Field - 3Four long straight thin wires are held vertically at the corners A, B, C and D of a square of side ‘a’, kept on a table and carry equal current ‘I’. The wire at A carries current in upward direction whereas the current in the remaining wires flows in downward direction. The net magnetic field at the centre of the square will have the magnitude :
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Ampere's Circuital Law and the Solenoid - 3A long straight wire of circular cross-section (radius a) carries a steady current I. The current is uniformly distributed across this cross-section. The magnitude of the magnetic field produced at a point at a distance (a/2) from the axis of the wire will be
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Ampere's Circuital Law and the Solenoid - 5A straight long wire lying along y-axis, carries a current of 1 A along direction. The magnetic field due to the conductor at a point (50 cm, 0, 0) will point along.
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Biot-Savart Law and Field of a Circular Loop - 5A charged particle is moving in a uniform magnetic field with a constant speed v in a circular path of radius r. Which of the following graphs represents the variation of radius of the circle, with the magnitude of magnetic field ?
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Magnetic Force and Motion in a Magnetic Field - 5A person is standing facing geographic north and a vertical wire in front of him is carrying a current in downward direction. The direction of magnetic field at a point on the right side of wire is
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Biot-Savart Law and Field of a Circular Loop - 7A galvanometer of resistance 27 is converted into an ammeter of range (0 – 10 mA) using a resistance of 3 . The galvanometer will show full scale deflection for a current of about –
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The Moving Coil Galvanometer - 8A charged particle of mass m having kinetic energy K passes undeflected through a region with electric field and magnetic field acting perpendicular to each other. The mass m of the particle will be :
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Magnetic Force and Motion in a Magnetic Field - 8A coil having 100 closely wound turns and area of cross-section carries a current of 5 mA. The magnitude of the magnetic moment associated with the coil is :
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Torque on a Current Loop and Magnetic Dipole - 9A straight conductor lies along -axis. It carries a current of 10 A along direction. The magnetic field due to 1 cm segment of this conductor, centred at the origin, at a point (0, 1 m, 0) is
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Biot-Savart Law and Field of a Circular Loop - 9A straight conductor lies along -axis and carries a current of 2 A along direction. The magnetic field at a point (0, 40 cm, 0) due to 1 cm length of conductor centered at the origin points along.
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Biot-Savart Law and Field of a Circular Loop - 10A circular loop has radius R and carries current I as shown in figure. In order that the net magnetic field at the centre of the loop is zero, the current in wire AB should have magnitude
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Biot-Savart Law and Field of a Circular Loop - 11A galvanometer of resistance G is converted into a voltmeter of range (0 – V) by connecting a resistor of 250 with it. If resistor of 250 is replaced by another resistor of 900 , its range becomes (0 – 3 V). The resistance G of the galvanometer is :
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The Moving Coil Galvanometer - Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.14Assertion (A) : The cylindrical soft iron core in a moving coil galvanometer only makes the magnetic field radial and does not affect the strength of the magnetic field. Reason (R) : In a moving coil galvanometer, the plane of the coil is always perpendicular to the magnetic field.
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The Moving Coil Galvanometer - 19A wire of length L is bent round into (i) a square coil having N turns and (ii) a circular coil having N turns. The coil in both cases is free to turn about a vertical axis coinciding with the plane of the coil, in a uniform, horizontal magnetic field and carry the same currents. Find the ratio of the maximum value of the torque acting on the square coil to that on the circular coil.Torque on a Current Loop and Magnetic Dipole
- 23 (a)A circular coil of 30 turns and radius cm carrying a current of 6 A is suspended vertically in a uniform horizontal magnetic field of T. The field lines make an angle of with the plane of the coil. Calculate the magnitude of the external torque that must be applied to prevent the coil from turning. What would happen if the circular coil is replaced by a planar coil of irregular shape that encloses the same area, keeping other parameters unchanged ?Torque on a Current Loop and Magnetic Dipole
- 23 (a)The figure given below shows three straight long parallel conductors , and kept in x-y plane, carrying currents 2I, I and 3I respectively as shown in figure. Find the magnitude and direction of : (i) net magnetic field at a point on conductor and (ii) net magnetic force acting on unit length of conductor , due to conductors and .Force Between Parallel Currents
- 23Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field at a point (1 m, 1 m, 0).Biot-Savart Law and Field of a Circular Loop
- 23 (b)An alpha particle (mass kg and charge C) having MeV energy, enters a region of a uniform magnetic field of T. If the field is directed perpendicular to the velocity of the particle, find the radius of the circular path described by the particle. Mention the condition under which the particle in this region (i) describes a helical path, and (ii) goes straight undeviated.Magnetic Force and Motion in a Magnetic Field
- 25 (b)Two long straight parallel conductors A and B carrying steady currents and in the same direction are separated by a distance d. Deduce the expressions for the force acting on length L of conductor B due to conductor A and show it in figure. Write the expression for the force acting on length L of conductor A due to conductor B and show that it follows Newton's third law.Force Between Parallel Currents
- 28Derive an expression for the magnetic field , due to a circular coil of N turns, each of radius r carrying current I, at a distance '' from the centre along its axis.Biot-Savart Law and Field of a Circular Loop
- A galvanometer is used to detect or/and measure small currents in an electrical circuit. It essentially works on the fact that a current-carrying coil experiences a deflecting torque when placed in a magnetic field. This deflection in the coil can be measured and it is related to the current flowing in the coil, the number of turns in the coil, area of the coil and the magnetic field. A hair spring attached to the coil provides a counter torque and helps in measuring the deflection. A galvanometer can be converted to an ammeter or a voltmeter of desired range by using suitable resistances.29 (I)The torque on the coil remains constant irrespective of the coil's orientation during rotation due to
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The Moving Coil Galvanometer - A galvanometer is used to detect or/and measure small currents in an electrical circuit. It essentially works on the fact that a current-carrying coil experiences a deflecting torque when placed in a magnetic field. This deflection in the coil can be measured and it is related to the current flowing in the coil, the number of turns in the coil, area of the coil and the magnetic field. A hair spring attached to the coil provides a counter torque and helps in measuring the deflection. A galvanometer can be converted to an ammeter or a voltmeter of desired range by using suitable resistances.29 (II)The best way to increase current sensitivity of a galvanometer is by
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The Moving Coil Galvanometer - A galvanometer is used to detect or/and measure small currents in an electrical circuit. It essentially works on the fact that a current-carrying coil experiences a deflecting torque when placed in a magnetic field. This deflection in the coil can be measured and it is related to the current flowing in the coil, the number of turns in the coil, area of the coil and the magnetic field. A hair spring attached to the coil provides a counter torque and helps in measuring the deflection. A galvanometer can be converted to an ammeter or a voltmeter of desired range by using suitable resistances.29 (III) (a)A moving coil galvanometer has a coil with area of cross-section and number of turns 50. The coil is rotating in a magnetic field of 0.25 T. The torque acting on the coil when a current of 5 A passes through it is
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The Moving Coil Galvanometer - A galvanometer is used to detect or/and measure small currents in an electrical circuit. It essentially works on the fact that a current-carrying coil experiences a deflecting torque when placed in a magnetic field. This deflection in the coil can be measured and it is related to the current flowing in the coil, the number of turns in the coil, area of the coil and the magnetic field. A hair spring attached to the coil provides a counter torque and helps in measuring the deflection. A galvanometer can be converted to an ammeter or a voltmeter of desired range by using suitable resistances.29 (III) (b)A galvanometer coil has a resistance of 15 and the meter shows full scale deflection for a current of 3 mA. The value of resistance required to convert it into a voltmeter of range (0 – 12 V) is
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The Moving Coil Galvanometer - A galvanometer is used to detect or/and measure small currents in an electrical circuit. It essentially works on the fact that a current-carrying coil experiences a deflecting torque when placed in a magnetic field. This deflection in the coil can be measured and it is related to the current flowing in the coil, the number of turns in the coil, area of the coil and the magnetic field. A hair spring attached to the coil provides a counter torque and helps in measuring the deflection. A galvanometer can be converted to an ammeter or a voltmeter of desired range by using suitable resistances.29 (IV)A galvanometer with coil of resistance 20 shows full scale deflection for a current of 5 mA. To convert it into an ammeter of range (0 – 10 A), a resistance of
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The Moving Coil Galvanometer - A charged particle +q in an electric field experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field . But this magnetic force is perpendicular to both velocity of the charged particle and the magnetic field , so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses m and having charges and respectively. They are accelerated from rest through the same potential difference V and acquire kinetic energy and . Then they enter in a region of uniform magnetic field perpendicular to their velocities.30 (i)The ratio of their kinetic energies is :
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Magnetic Force and Motion in a Magnetic Field - A charged particle +q in an electric field experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field . But this magnetic force is perpendicular to both velocity of the charged particle and the magnetic field , so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses m and having charges and respectively. They are accelerated from rest through the same potential difference V and acquire kinetic energy and . Then they enter in a region of uniform magnetic field perpendicular to their velocities.30 (ii)The ratio of the radii of the circular paths described by them is :
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Magnetic Force and Motion in a Magnetic Field - A charged particle +q in an electric field experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field . But this magnetic force is perpendicular to both velocity of the charged particle and the magnetic field , so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses m and having charges and respectively. They are accelerated from rest through the same potential difference V and acquire kinetic energy and . Then they enter in a region of uniform magnetic field perpendicular to their velocities.30 (iii)Suppose particles 1 and 2 enter the magnetic field with velocities and . Then :
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Magnetic Force and Motion in a Magnetic Field - A charged particle +q in an electric field experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field . But this magnetic force is perpendicular to both velocity of the charged particle and the magnetic field , so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses m and having charges and respectively. They are accelerated from rest through the same potential difference V and acquire kinetic energy and . Then they enter in a region of uniform magnetic field perpendicular to their velocities.30 (iv) (a)If period of revolution for particle 1 is 4 s, then for particle 2, the period will be :
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Magnetic Force and Motion in a Magnetic Field - A charged particle +q in an electric field experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field . But this magnetic force is perpendicular to both velocity of the charged particle and the magnetic field , so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses m and having charges and respectively. They are accelerated from rest through the same potential difference V and acquire kinetic energy and . Then they enter in a region of uniform magnetic field perpendicular to their velocities.30 (iv) (b)If the value of momentum for particles 1 and 2 are and , then :
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Magnetic Force and Motion in a Magnetic Field - 32 (a)(i) A rectangular loop of sides a and b carrying current I is placed in a magnetic field such that its area vector makes an angle with . With the help of a suitable diagram, show that the torque acting on the loop is given by , where is the magnetic dipole moment of the loop. (ii) A circular coil of 100 turns and radius cm carrying current of A is suspended vertically in a uniform horizontal magnetic field of T. The field makes an angle with the normal to the coil. Calculate : (I) the magnetic dipole moment of the coil, and (II) the magnitude of the counter torque that must be applied to prevent the coil from turning.Torque on a Current Loop and Magnetic Dipole
- 32 (b)(i) Derive an expression for the force acting on a conductor of length L and area of cross-section A carrying current I and placed in a magnetic field . (ii) A part of a wire carrying A current and bent at at two points is placed in a region of uniform magnetic field , as shown in the figure. Calculate the magnitude of the net force acting on the wire.Magnetic Force and Motion in a Magnetic Field
2025
43 q
- 3A 1 cm straight segment of a conductor carrying 1 A current in direction lies symmetrically at origin of Cartesian coordinate system. The magnetic field due to this segment at point (1m, 1m, 0) is
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Biot-Savart Law and Field of a Circular Loop - 3A straight conductor is carrying a current of 2 A in +x direction along it. A uniform magnetic field T is switched on, in the region. The force acting on 10 cm length of the conductor is :
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Magnetic Force and Motion in a Magnetic Field - 3A particle with charge q moving with velocity enters a region with magnetic field . The magnitude of force experienced by the particle is :
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Magnetic Force and Motion in a Magnetic Field - 3In a circular loop of radius R, current I enters at point A and exits at point B, as shown in the figure. The value of the magnetic field at the centre O of the loop is :
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Biot-Savart Law and Field of a Circular Loop - 3A particle of mass m and charge q moves along y-axis in a region in which a uniform magnetic field is pointing along x-axis. The Lorentz force acting on the charge will point along :
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Magnetic Force and Motion in a Magnetic Field - 3The value of magnetic field at point O in the given figure is :
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Biot-Savart Law and Field of a Circular Loop - 3A particle having charge +q enters a uniform magnetic field as shown in the figure. The particle will describe :
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Magnetic Force and Motion in a Magnetic Field - 3A 1 cm segment of a wire lying along x-axis carries current of 0.5 A along +x direction. A magnetic field is switched on, in the region. The force acting on the segment is
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Magnetic Force and Motion in a Magnetic Field - 4A charged particle gains a speed of , when accelerated from rest through a potential difference 10 kV. It enters a region of magnetic field of T such that . The radius of circular path described by it is :
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Magnetic Force and Motion in a Magnetic Field - 5A current of A is maintained in a circular loop of radius 14 cm. The value of dipole moment associated with the loop is :
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Torque on a Current Loop and Magnetic Dipole - 5A galvanometer can be converted into an ammeter of desired range by connecting a :
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The Moving Coil Galvanometer - 6A proton and an -particle enter with the same velocity in a uniform magnetic field such that . The ratio of the radii of their paths is :
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Magnetic Force and Motion in a Magnetic Field - 12A long straight wire is held vertically and carries a steady current in upward direction. The shape of magnetic field lines produced by the current-carrying wire are :
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Ampere's Circuital Law and the Solenoid - Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.13Assertion (A) : A charged particle is moving with velocity v in x-y plane, making an angle with x-axis. If a uniform magnetic field is applied in the region, along y-axis, the particle will move in a helical path with its axis parallel to x-axis. Reason (R) : The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.
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Magnetic Force and Motion in a Magnetic Field - Note : Question numbers 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given – one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below :14Assertion (A) : The deflection in a galvanometer is directly proportional to the current passing through it. Reason (R) : The coil of a galvanometer is suspended in a uniform radial magnetic field.
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The Moving Coil Galvanometer - 18A current of 5 A is passing along +X direction through a wire lying along X-axis. Find the magnetic field at a point m due to 1 cm element of the wire, centered at origin.Biot-Savart Law and Field of a Circular Loop
- 19A circular coil of wire having 200 turns, each of radius cm is placed in a horizontal plane. It carries a current of A in clockwise direction. Find the magnitude and direction of the magnetic field at the centre of the coil.Biot-Savart Law and Field of a Circular Loop
- 19A voltmeter of resistance 1000 can measure up to 25 V. How will you convert it so that it can read up to 250 V ?The Moving Coil Galvanometer
- 23 (a)In a region of a uniform electric field , a negatively charged particle is moving with a constant velocity near a long straight conductor coinciding with axis and carrying current I towards X axis. The particle remains at a distance d from the conductor. (i) Draw diagram showing direction of electric and magnetic fields. (ii) What are the various forces acting on the charged particle ? (iii) Find the value of in terms of E, d and I.Magnetic Force and Motion in a Magnetic Field
- 23A rectangular loop carries a current of 1 A. A straight long wire carrying 2 A current is kept near the loop in the same plane as shown in the figure. Find : (i) the torque acting on the loop, and (ii) the magnitude and direction of the net force on the loop.Force Between Parallel Currents
- 23(a) In which cases does a charged particle not experience a force in a magnetic field ? (b) A square loop MNPK of side '' carrying a current '' is kept close to a long straight wire in the same plane and the wire carries a steady current as shown in the figure. Obtain the magnitude of magnetic force exerted by the wire on the loop.Force Between Parallel Currents
- 23(a) A charged particle q moving with a velocity is subjected to a uniform magnetic field acting perpendicular to . If a uniform electric field is also set up in the region along the direction of , describe the path followed by the particle and draw its shape. (b) How will the magnetic field inside a long solenoid be affected when : (i) the radius of the turns of the solenoid is increased, (ii) the length of solenoid as well as the total number of its turns are doubled ?Magnetic Force and Motion in a Magnetic Field
- 23 (a)(i) Write Biot-Savart's law in vector form. (ii) Two identical circular coils A and B, each of radius R, carrying currents I and respectively, are placed concentrically in XY and YZ planes respectively. Find the magnitude and direction of the net magnetic field at their common centre.Biot-Savart Law and Field of a Circular Loop
- 23 (b)(i) A rectangular loop of sides and b carries a current I clockwise. Write the magnetic moment of the loop and show its direction in a diagram. (ii) The loop is placed in a uniform magnetic field and is free to rotate about an axis which is perpendicular to . Prove that the loop experiences no net force, but a torque .Torque on a Current Loop and Magnetic Dipole
- 23Using Biot-Savart law, derive expression for the magnetic field due to a circular current carrying loop at a point on its axis and hence at its centre.Biot-Savart Law and Field of a Circular Loop
- 23A particle of charge q is moving with a velocity at a distance 'd' from a long straight wire carrying a current 'I' as shown in figure. At this instant, it is subjected to a uniform electric field such that the particle keeps moving undeviated. In terms of unit vectors , and , find - (a) the magnetic field , (b) the magnetic force , and (c) the electric field , acting on the charge.Magnetic Force and Motion in a Magnetic Field
- 23(a) Write vector form of Biot-Savart law. (b) Two insulated long straight wires, each carrying A current are kept along and axis as shown in the figure. Find the magnitude and direction of resultant magnetic field at point P (4m, 5m).Biot-Savart Law and Field of a Circular Loop
- 23(a) Define magnetic moment of a current-carrying coil. Write its SI unit. (b) A coil of 60 turns and area carrying 2A current lies in a vertical plane. It experiences a torque of 0.12 Nm when placed in a uniform horizontal magnetic field. The torque acting on the coil changes to 0.05 Nm after the coil is rotated about its diameter by , in the magnetic field. Find the magnitude of the magnetic field.Torque on a Current Loop and Magnetic Dipole
- 23 (b)Two infinitely long conductors kept along and axes are carrying current and along X axis and Y axis respectively. Find the magnitude and direction of the net magnetic field produced at point P(X, Y).Ampere's Circuital Law and the Solenoid
- 26An electron of mass m and charge is revolving anticlockwise around the nucleus of an atom. (a) Obtain the expression for the magnetic dipole moment of the atom. (b) If is the angular momentum of electron, show that .Torque on a Current Loop and Magnetic Dipole
- 27(a) Use Ampere's law to derive the expression for the magnetic field due to a long straight current carrying wire of infinite length. (b) Why is Ampere's law used for the derivation in (a) above and not Biot-Savart's law ? Explain.Ampere's Circuital Law and the Solenoid
- A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the surname of Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog's leg jerk. A spring attached with the coil provides a counter torque. In equilibrium, the deflecting torque is balanced by the restoring torque of the spring and we have : where N is the total number of turns in the coil A is the area of cross-section of each turn B is the radial magnetic field k is the torsional constant of the spring is the angular deflection of the coil As the current which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of desired range. By using a higher resistance, a galvanometer can also be converted into a voltmeter.29 (i)The value of the current sensitivity of a galvanometer is given by :
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The Moving Coil Galvanometer - A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the surname of Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog's leg jerk. A spring attached with the coil provides a counter torque. In equilibrium, the deflecting torque is balanced by the restoring torque of the spring and we have : where N is the total number of turns in the coil A is the area of cross-section of each turn B is the radial magnetic field k is the torsional constant of the spring is the angular deflection of the coil As the current which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of desired range. By using a higher resistance, a galvanometer can also be converted into a voltmeter.29 (ii)A galvanometer of resistance 6 shows full scale deflection for a current of A. The value of shunt to be used with this galvanometer to convert it into an ammeter of range A is :
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The Moving Coil Galvanometer - A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the surname of Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog's leg jerk. A spring attached with the coil provides a counter torque. In equilibrium, the deflecting torque is balanced by the restoring torque of the spring and we have : where N is the total number of turns in the coil A is the area of cross-section of each turn B is the radial magnetic field k is the torsional constant of the spring is the angular deflection of the coil As the current which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of desired range. By using a higher resistance, a galvanometer can also be converted into a voltmeter.29 (ii)The value of resistance of the ammeter in case (ii) will be :
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The Moving Coil Galvanometer - A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the surname of Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog's leg jerk. A spring attached with the coil provides a counter torque. In equilibrium, the deflecting torque is balanced by the restoring torque of the spring and we have : where N is the total number of turns in the coil A is the area of cross-section of each turn B is the radial magnetic field k is the torsional constant of the spring is the angular deflection of the coil As the current which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of desired range. By using a higher resistance, a galvanometer can also be converted into a voltmeter.29 (iii)The value of resistance of the ammeter in case (ii) will be :
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The Moving Coil Galvanometer - A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the surname of Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog's leg jerk. A spring attached with the coil provides a counter torque. In equilibrium, the deflecting torque is balanced by the restoring torque of the spring and we have : where N is the total number of turns in the coil A is the area of cross-section of each turn B is the radial magnetic field k is the torsional constant of the spring is the angular deflection of the coil As the current which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of desired range. By using a higher resistance, a galvanometer can also be converted into a voltmeter.29 (iv) (a)A galvanometer is converted into a voltmeter of range by connecting with it, a resistance . If is replaced by , the range becomes . The resistance of the galvanometer is :
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The Moving Coil Galvanometer - A galvanometer is an instrument used to show the direction and strength of the current passing through it. In a galvanometer, a coil placed in a magnetic field experiences a torque and hence gets deflected when a current passes through it. The name is derived from the surname of Italian scientist L. Galvani, who in 1791 discovered that electric current makes a dead frog's leg jerk. A spring attached with the coil provides a counter torque. In equilibrium, the deflecting torque is balanced by the restoring torque of the spring and we have : where N is the total number of turns in the coil A is the area of cross-section of each turn B is the radial magnetic field k is the torsional constant of the spring is the angular deflection of the coil As the current which produces full scale deflection in the galvanometer is very small, the galvanometer cannot as such be used to measure current in electric circuits. A small resistance, called shunt, of a suitable value is connected with the galvanometer to convert it into an ammeter of desired range. By using a higher resistance, a galvanometer can also be converted into a voltmeter.29 (iv) (b)A current of 5 mA flows through a galvanometer. Its coil has 100 turns, each of area of cross-section and is suspended in a magnetic field T. The deflecting torque acting on the coil will be :
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Torque on a Current Loop and Magnetic Dipole - 32 (a)(i) What is the source of force acting on a current-carrying conductor placed in a magnetic field ? Obtain the expression for force acting between two long straight parallel conductors carrying steady currents and hence define 'ampere'. (ii) A point charge q is moving with velocity in a uniform magnetic field . Find the work done by the magnetic force on the charge. (iii) Explain the necessary conditions in which the trajectory of a charged particle is helical in a uniform magnetic field.Force Between Parallel Currents
- 32 (a)(i) With the help of a labelled diagram, explain the principle of working of a moving coil galvanometer. Write the purpose of using (i) radial magnetic field, and (ii) soft iron core, in it. (ii) Define current sensitivity of a galvanometer. "Increasing the current sensitivity may not necessarily increase the voltage sensitivity." Give reason.The Moving Coil Galvanometer
- 32 (a)(i) A proton moving with velocity in a non-uniform magnetic field traces a path as shown in the figure. The path followed by the proton is always in the plane of the paper. What is the direction of the magnetic field in the region near points P, Q and R ? What can you say about relative magnitude of magnetic fields at these points ? (ii) A current carrying circular loop of area A produces a magnetic field B at its centre. Show that the magnetic moment of the loop is .Magnetic Force and Motion in a Magnetic Field
- 32 (b)(i) A current carrying loop can be considered as a magnetic dipole placed along its axis. Explain. (ii) Obtain the relation for magnetic dipole moment of current carrying coil. Give the direction of . (iii) A current carrying coil is placed in an external uniform magnetic field. The coil is free to turn in the magnetic field. What is the net force acting on the coil ? Obtain the orientation of the coil in stable equilibrium. Show that in this orientation the flux of the total field (field produced by the loop + external field) through the coil is maximum.Torque on a Current Loop and Magnetic Dipole
- 32 (b)(i) Derive an expression for the torque acting on a rectangular current loop suspended in a uniform magnetic field. (ii) A charged particle is moving in a circular path with velocity in a uniform magnetic field . It is made to pass through a sheet of lead and as a consequence, it looses one half of its kinetic energy without change in its direction. How will (1) the radius of its path (2) its time period of revolution change ?Torque on a Current Loop and Magnetic Dipole
- 32 (b)(i) (I) Write Ampere's circuital law in mathematical form and explain the terms used. (II) As the current carrying solenoid is made longer, the magnetic field produced outside it approaches zero. Why ? (III) A flexible loop of irregular shape carrying current when located in an external magnetic field, changes to a circular shape. Give reason. (ii) A galvanometer of resistance G is converted into a voltmeter to measure up to V volts, by connecting a resistance in series with the coil. If is replaced by , then it can only measure up to volt. Find the value of the resistance (in terms of and ) needed to convert it into a voltmeter that can read up to 2 V.Ampere's Circuital Law and the Solenoid
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- 2A particle of mass m and charge q describes a circular path of radius R in a magnetic field. If its mass and charge were 2 m and respectively, the radius of its path would be
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Magnetic Force and Motion in a Magnetic Field - 2Two insulated concentric coils, each of radius R, placed at right angles to each other, carry currents I and I respectively. The magnitude of the net magnetic field at their common centre will be
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Biot-Savart Law and Field of a Circular Loop - 3A wire of length m is bent round in the shape of a circular loop and carries a current of A. The magnetic moment of the loop will be :
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Torque on a Current Loop and Magnetic Dipole - 3A cm segment of wire, carrying A current in positive y-direction lies along y-axis, as shown in the figure. The magnetic field at a point (3 m, 4 m, 0) due to this segment (part of a circuit) is :
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Biot-Savart Law and Field of a Circular Loop - 4A circular loop of wire, carrying a current 'I' is lying in xy-plane with its centre coinciding with the origin. It is subjected to a uniform magnetic field pointing along + z-axis. The loop will :
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Torque on a Current Loop and Magnetic Dipole - 4Two charged particles, P and Q, each having charge q but of masses and , are accelerated through the same potential difference V. They enter a region of magnetic field and describe the circular paths of radii a and b respectively. Then is equal to :
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Magnetic Force and Motion in a Magnetic Field - 4A galvanometer of resistance is converted into a voltmeter of range using a resistor of . If it is to be converted into a voltmeter of range , the resistance required will be
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The Moving Coil Galvanometer - 4A galvanometer shows full scale deflection for a current . If a shunt of resistance is connected to the galvanometer, it gets converted into an ammeter of range . When resistance of the shunt is made , its range becomes . Then is
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The Moving Coil Galvanometer - 4Two thin long parallel wires separated by a distance 'a' carry current 'I' in opposite directions. The wires will :
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Force Between Parallel Currents - 4A piece of wire bent in the form of a circular loop A carries a current I. The wire is then bent into a circular loop B of two turns and carries the same current. The ratio of magnetic fields at the centre of loop A to that of loop B will be :
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Biot-Savart Law and Field of a Circular Loop - 4A galvanometer of resistance gives full scale deflection for a current of 1.0 mA. It is converted into an ammeter of range . The resistance of the ammeter will be close to
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The Moving Coil Galvanometer - 4A loop carrying a current I clockwise is placed in plane, in a uniform magnetic field directed along z-axis. The tendency of the loop will be to :
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Torque on a Current Loop and Magnetic Dipole - 5A particle of mass m and charge q is moving with velocity . If it is subjected to a magnetic field , it will move in a -
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Magnetic Force and Motion in a Magnetic Field - 5Two long straight parallel conductors A and B, kept at a distance r, carry current I in opposite directions. A third identical conductor C, kept at a distance from A carry current in the same direction as in A. The net magnetic force on unit length of C is
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Force Between Parallel Currents - 5A current carrying circular loop of magnetic moment is suspended in a vertical plane in an external magnetic field such that its plane is normal to . The work done in rotating this loop by about an axis perpendicular to is closest to :
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Torque on a Current Loop and Magnetic Dipole - 5A straight wire is kept horizontally along east-west direction. If a steady current flows in wire from east to west, the magnetic field at a point above the wire will point towards
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Biot-Savart Law and Field of a Circular Loop - 5A 10 cm long wire lies along y-axis. It carries a current of A in positive y-direction. A magnetic field exists in the region. The force on the wire is :
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Magnetic Force and Motion in a Magnetic Field - 6A galvanometer of resistance G is converted into an ammeter of range 0 to I A. If the current through the galvanometer is of I A, the resistance of the ammeter is :
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The Moving Coil Galvanometer - 7A galvanometer of resistance 100 is converted into an ammeter of range using a resistance of 0.1 . The ammeter will show full scale deflection for a current of about
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The Moving Coil Galvanometer - For Questions 13 to 16, two statements are given – one labelled Assertion (A) and other labelled Reason (R). Select the correct answer to these questions from the options as given below. (A) If both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A). (B) If both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A). (C) If Assertion (A) is true but Reason (R) is false. (D) If both Assertion (A) and Reason (R) are false.14Assertion (A) : The energy of a charged particle moving in a magnetic field does not change. Reason (R) : It is because the work done by the magnetic force on the charge moving in a magnetic field is zero.
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Magnetic Force and Motion in a Magnetic Field - Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.15Assertion (A) : An electron and a proton enter with the same momentum in a magnetic field such that . Then both describe a circular path of the same radius. Reason (R) : The radius of the circular path described by the charged particle (charge q, mass m) moving in the magnetic field is given by .
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Magnetic Force and Motion in a Magnetic Field - Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.15Assertion (A) : Two long parallel wires, freely suspended and connected in series to a battery, move apart. Reason (R) : Two wires carrying current in opposite directions repel each other.
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Force Between Parallel Currents - Questions number 13 to 16 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.15Assertion (A) : A proton and an electron enter a uniform magnetic field with the same momentum such that is perpendicular to . They describe circular paths of the same radius. Reason (R) : In a magnetic field, orbital radius r is equal to .
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Magnetic Force and Motion in a Magnetic Field - 18Derive an expression for magnetic force acting on a straight conductor of length L carrying current I in an external magnetic field . Is it valid when the conductor is in zig-zag form ? Justify.Magnetic Force and Motion in a Magnetic Field
- 23Two long straight parallel conductors carrying currents, exert a force on each other. Why ? Derive an expression for the force per unit length between two long straight parallel conductors carrying currents in opposite directions. Explain the nature of the force between these conductors.Force Between Parallel Currents
- 23An electron (charge , mass m) is revolving around a nucleus, in a hydrogen atom, in a circle of radius r. Derive an expression, in vector form, for the magnetic dipole moment, in terms of its orbital angular momentum . What is gyromagnetic ratio ?Torque on a Current Loop and Magnetic Dipole
- 23A rectangular loop of area , carrying current I, is placed in a uniform magnetic field . With the help of a suitable diagram, derive an expression, in vector form, for the torque acting on the loop.Torque on a Current Loop and Magnetic Dipole
- 24A circular coil with cross-sectional area carries a current of 4 A. It is kept in a uniform magnetic field of magnitude T normal to the plane of the coil. Calculate : (a) the net force on the coil. (b) the torque on the coil. (c) the average force on each electron in the coil due to the magnetic field. The free electron density in the material of the coil is .Torque on a Current Loop and Magnetic Dipole
- 25Two long insulated straight wires carrying currents of 3 A and 5 A are arranged in XY plane as shown in figure. Find the magnitude and direction of the net magnetic fields at points (2m, 2m) and (-1m, 1m).Biot-Savart Law and Field of a Circular Loop
- 24 (b)(i) State and explain Ampere's circuital law. (ii) Two long straight parallel wires separated by 20 cm, carry 5 A and 10 A current respectively, in the same direction. Find the magnitude and direction of the net magnetic field at a point midway between them.Ampere's Circuital Law and the Solenoid
- 24A proton with kinetic energy J moving horizontally from north to south, enters a uniform magnetic field B of mT directed eastward. Calculate : (a) the speed of the proton (b) the magnitude of acceleration of the proton (c) the radius of the path traced by the proton [Take (q/m) for proton = C/kg]Magnetic Force and Motion in a Magnetic Field
- 25 (a)Two long, straight, parallel conductors carry steady currents in opposite directions. Explain the nature of the force of interaction between them. Obtain an expression for the magnitude of the force between the two conductors. Hence define one ampere.Force Between Parallel Currents
- 25An electron moving with a velocity enters a region of uniform magnetic field . Find the radius of the circular path described by it. While rotating; does the electron trace a linear path too ? If so, calculate the linear distance covered by it during the period of one revolution.Magnetic Force and Motion in a Magnetic Field
- 26A circular loop of radius 10 cm carrying current of 1.0 A lies in - plane. A long straight wire lies in the same plane parallel to -axis at a distance of 20 cm as shown in figure. Find the direction and value of current that has to be maintained in the wire so that the net magnetic field at O is zero.Biot-Savart Law and Field of a Circular Loop
- 25 (b)Obtain an expression for the torque acting on a current carrying loop in a uniform magnetic field . Draw the necessary diagram.Torque on a Current Loop and Magnetic Dipole
- 26An infinite straight conductor is kept along axis and carries a current I. A charge q at point P(0, r) starts moving with velocity as shown in figure. Find the direction and magnitude of force initially experienced by the charge.Magnetic Force and Motion in a Magnetic Field
- 27An electron is moving with a velocity . It enters a region of magnetic field . (a) Calculate the magnetic force acting on electron and the radius of its path. (b) Trace the path described by it.Magnetic Force and Motion in a Magnetic Field
- 32 (a)(i) (1) What is meant by current sensitivity of a galvanometer ? Mention the factors on which it depends. (2) A galvanometer of resistance G is converted into a voltmeter of range (0 – V) by using a resistance R. Find the resistance, in terms of R and G, required to convert it into a voltmeter of range . (ii) The magnetic flux through a coil of resistance 5 increases with time as : mWb Find the magnitude of induced current through the coil at t = 2 s.The Moving Coil Galvanometer
- 32 (a)(i) A particle of mass m and charge q is moving with a velocity in a magnetic field as shown in the figure. Show that it follows a helical path. Hence, obtain its frequency of revolution. (ii) In a hydrogen atom, the electron moves in an orbit of radius making revolutions per second. Find the magnetic moment associated with the orbital motion of the electron.Magnetic Force and Motion in a Magnetic Field
- 32 (b)(i) What is current sensitivity of a galvanometer ? Show how the current sensitivity of a galvanometer may be increased. "Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage sensitivity." Explain. (ii) A moving coil galvanometer has a resistance and takes 20 mA to produce full scale deflection. How can this galvanometer be converted into a voltmeter of range 0 to 100 V ?The Moving Coil Galvanometer
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- 2Two long parallel wires kept 2 m apart carry 3A current each, in the same direction. The force per unit length on one wire due to the other is
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Force Between Parallel Currents - 2Two horizontal thin long parallel wires, separated by a distance r carry current I each in the opposite directions. The net magnetic field at a point midway between them, will be
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Force Between Parallel Currents - 2An electron enters a uniform magnetic field with speed . It describes a semicircular path and comes out of the field. The final speed of the electron is :
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Magnetic Force and Motion in a Magnetic Field - 3Two thin long parallel wires A and B are separated by a distance r and carry current I each in the same direction. The force per unit length exerted by A on wire B is :
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Force Between Parallel Currents - 4Which of the following graphs correctly represents the variation of the magnitude of the magnetic field outside a straight infinite current carrying wire of radius ‘a’, as a function of distance ‘r’ from the centre of the wire ?
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Ampere's Circuital Law and the Solenoid - 5A particle of mass m and charge q moving with a uniform velocity enters a region with a magnetic field . After some time, an electric field is also switched on in the region. The resulting path described by the particle will be :
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Magnetic Force and Motion in a Magnetic Field - 5Beams of electrons and protons move parallel to each other in the same direction. They
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Force Between Parallel Currents - 6A long straight wire of radius 'a' carries a steady current 'I'. The current is uniformly distributed across its area of cross-section. The ratio of magnitude of magnetic field at and at distance 2a is
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Ampere's Circuital Law and the Solenoid - 7The ratio of the magnitude of magnetic moment to that of angular momentum, of an electron revolving around the nucleus in a hydrogen atom is :
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Torque on a Current Loop and Magnetic Dipole - 10In a moving coil galvanometer, the deflecting torque acting on the coil is related to the current I flowing through it as :
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The Moving Coil Galvanometer - Questions number 16 to 18 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.17Assertion (A) : A current carrying square loop made of a wire of length L is placed in a magnetic field. It experiences a torque which is greater than the torque on a circular loop made of the same wire carrying the same current in the same magnetic field. Reason (R) : A square loop occupies more area than a circular loop, both made of wire of the same length.
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Torque on a Current Loop and Magnetic Dipole - Questions number 16 to 18 are Assertion (A) and Reason (R) type questions. Two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (a), (b), (c) and (d) as given below.17Assertion (A) : When radius of a circular loop carrying a steady current is doubled, its magnetic moment becomes four times. Reason (R) : The magnetic moment of a circular loop carrying a steady current is proportional to the area of the loop.
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Torque on a Current Loop and Magnetic Dipole - In question number 16 to 18 two statements are given – one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below : (A) Both Assertion (A) and Reason (R) are true and (R) is the correct explanation of (A). (B) Both Assertion (A) and Reason (R) are true and (R) is NOT the correct explanation of (A). (C) Assertion (A) is true and Reason (R) is false. (D) Assertion (A) is false and Reason (R) is also false.18Assertion (A) : The deflecting torque acting on a current carrying loop is zero when its plane is perpendicular to the direction of magnetic field. Reason (R) : The deflecting torque acting on a loop of magnetic moment in a magnetic field is given by the dot product of and .
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Torque on a Current Loop and Magnetic Dipole - 19An alpha particle is projected with velocity into a region in which magnetic field exists. Calculate the acceleration of the particle in the region. , and are unit vectors along x, y and z axis respectively and charge to mass ratio for alpha particle is C/kg.Magnetic Force and Motion in a Magnetic Field
- 19Briefly explain why and how a galvanometer is converted into an ammeter.The Moving Coil Galvanometer
- 19A wire of length is in the form of a circular loop A of one turn. This loop is reshaped into loop B of three turns. Find the ratio of the magnetic fields at the centres of loop A and loop B for the same current through them.Biot-Savart Law and Field of a Circular Loop
- 22A wire of length L is bent round in the form of (i) a square, and then (ii) an equilateral triangle. If current I is passed through each of them, find the ratio of magnetic moment of the square loop to that of the triangle.Torque on a Current Loop and Magnetic Dipole
- 23A particle of charge q and mass m starts moving with uniform velocity . Specify the direction of magnetic field which should be set up in the region so that the particle moves (a) straight undeviated, and (b) in a circle. Justify your answers.Magnetic Force and Motion in a Magnetic Field
- 23 (a)Write the expression for the Lorentz force on a particle of charge q moving with a velocity in a magnetic field . When is the magnitude of this force maximum ? Show that no work is done by this force on the particle during its motion from a point to point .Magnetic Force and Motion in a Magnetic Field
- 23Two wires of equal lengths are shaped in the form of a square loop and a circular loop. Both loops are suspended in a uniform magnetic field. Prove that for the same current, the circular loop will experience larger torque.Torque on a Current Loop and Magnetic Dipole
- 23 (a)Two identical circular loops P and Q, each of radius R carrying current I are kept in perpendicular planes such that they have a common centre O as shown in the figure. Find the magnitude and direction of the net magnetic field at point O.Biot-Savart Law and Field of a Circular Loop
- 23 (b)A long straight wire AB carries a current I. A particle (mass m and charge q) moves with a velocity , parallel to the wire, at a distance d from it as shown in the figure. Obtain the expression for the force experienced by the particle and mention its directions.Magnetic Force and Motion in a Magnetic Field
- 23 (b)A long straight conductor kept along X' X axis, carries a steady current I along direction. At an instant t, a particle of mass m and charge q at point moves with a velocity along direction. Find the magnitude and direction of the force on the particle due to the conductor.Magnetic Force and Motion in a Magnetic Field
- 26Two circular loops A and B, each of radius 3 m, are placed coaxially at a distance of 4 m. They carry currents of 3 A and 2 A in opposite directions respectively. Find the net magnetic field at the centre of loop A.Biot-Savart Law and Field of a Circular Loop
- 27A current carrying circular loop and a straight wire bent partly in the form of a semicircle are placed as shown in the figure. Find the magnitude and direction of net magnetic field at point O.Biot-Savart Law and Field of a Circular Loop
- 29(a) Briefly describe how the current sensitivity of a moving coil galvanometer can be increased. (b) A galvanometer shows full scale deflection for current . A resistance is required to convert it into a voltmeter of range and a resistance to convert it into a voltmeter of range . Find the resistance of the galvanometer.The Moving Coil Galvanometer
- 29Two infinitely long parallel conductors A and B, separated by 2 cm, carry 6 A and 2 A currents in opposite directions respectively. Find : (a) the net magnetic field at a point midway between A and B. (b) the force acting per unit length on B.Force Between Parallel Currents
- 32 (a)(i) Write the principle and explain the working of a moving coil galvanometer. A galvanometer as such cannot be used to measure the current in a circuit. Why ? (ii) Why is the magnetic field made radial in a moving coil galvanometer ? How is it achieved ?The Moving Coil Galvanometer
- 32 (a)(i) State Biot-Savart's law for the magnetic field due to a current carrying element. Use this law to obtain an expression for the magnetic field at the centre of a circular loop of radius 'a' and carrying a current 'I'. Draw the magnetic field lines for a current loop indicating the direction of magnetic field. (ii) An electron is revolving around the nucleus in a circular orbit with a speed of . If the radius of the orbit is m, find the current constituted by the revolving electron in the orbit.Biot-Savart Law and Field of a Circular Loop
- 32 (b)(i) Derive an expression for magnetic field on the axis of a current carrying circular loop. (ii) Write any two points of difference between a diamagnetic and a paramagnetic substance.Biot-Savart Law and Field of a Circular Loop
- 32 (b)(i) Derive an expression for the force acting on a current carrying straight conductor kept in a magnetic field. State the rule which is used to find the direction of this force. Give the condition under which this force is (1) maximum, and (2) minimum. (ii) Two long parallel straight wires A and B are cm apart in air. They carry A and A currents respectively in opposite directions. Calculate the magnitude of the force exerted by wire A on a 10 cm length of wire B.Magnetic Force and Motion in a Magnetic Field
- A beam of electrons moving horizontally with a velocity of m/s enters a region between two plates as shown in the figure. A suitable potential difference is applied across the plates such that the electron beam just strikes the edge of the lower plate.34 (c)Find the magnitude and direction of the magnetic field which should be created in the space between the plates so that the electron beam goes straight undeviated.Magnetic Force and Motion in a Magnetic Field
- 34 (b)Briefly explain various ways to increase the strength of magnetic field produced by a given solenoid.Ampere's Circuital Law and the Solenoid
The 10 board questions to practise first
The questions the board asked again come first, most asked first. Each one says how often and when.
Question 1
Asked 3 times: 2023*, 2024, 2025 (* = numbers or wording changed that year)
23 (a)(i) Write Biot-Savart's law in vector form. (ii) Two identical circular coils A and B, each of radius R, carrying currents I and respectively, are placed concentrically in XY and YZ planes respectively. Find the magnitude and direction of the net magnetic field at their common centre.Question 2
Asked 2 times: 2025*, 2026 (* = numbers or wording changed that year)
23Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field at a point (1 m, 1 m, 0).Question 3
Asked 2 times: 2025, 2026
28Derive an expression for the magnetic field , due to a circular coil of N turns, each of radius r carrying current I, at a distance '' from the centre along its axis.Question 4
Asked 2 times: 2024, 2026
25 (b)Two long straight parallel conductors A and B carrying steady currents and in the same direction are separated by a distance d. Deduce the expressions for the force acting on length L of conductor B due to conductor A and show it in figure. Write the expression for the force acting on length L of conductor A due to conductor B and show that it follows Newton's third law.Question 5
Asked 2 times: 2023, 2026
19A wire of length L is bent round into (i) a square coil having N turns and (ii) a circular coil having N turns. The coil in both cases is free to turn about a vertical axis coinciding with the plane of the coil, in a uniform, horizontal magnetic field and carry the same currents. Find the ratio of the maximum value of the torque acting on the square coil to that on the circular coil.Question 6
Asked 2 times: 2024*, 2026 (* = numbers or wording changed that year)
7A galvanometer of resistance 27 is converted into an ammeter of range (0 – 10 mA) using a resistance of 3 . The galvanometer will show full scale deflection for a current of about –Tap an option to check your answer.
Question 7
Asked 2 times: 2024*, 2025 (* = numbers or wording changed that year)
18A current of 5 A is passing along +X direction through a wire lying along X-axis. Find the magnetic field at a point m due to 1 cm element of the wire, centered at origin.Question 8
Asked 2 times: 2024, 2025
23 (b)(i) A rectangular loop of sides and b carries a current I clockwise. Write the magnetic moment of the loop and show its direction in a diagram. (ii) The loop is placed in a uniform magnetic field and is free to rotate about an axis which is perpendicular to . Prove that the loop experiences no net force, but a torque .Question 9
Asked 2 times: 2024, 2025
26An electron of mass m and charge is revolving anticlockwise around the nucleus of an atom. (a) Obtain the expression for the magnetic dipole moment of the atom. (b) If is the angular momentum of electron, show that .Question 10
Asked 2 times: 2023*, 2024 (* = numbers or wording changed that year)
4A piece of wire bent in the form of a circular loop A carries a current I. The wire is then bent into a circular loop B of two turns and carries the same current. The ratio of magnetic fields at the centre of loop A to that of loop B will be :Tap an option to check your answer.