Physics · Textbook solutions

Electrostatics

Every solved example, exercise, and miscellaneous question — in the order the textbook teaches them. · 32 questions

10. Electrostatics — worked examples

9 q

Solved Examples

Worked · 9
  1. Solved Ex.10.1
    How much positive and negative charge is present in 1gm of water? How many electrons are present in it? Given, molecular mass of water is 18.0 g.
  2. Solved Ex.10.2
    Charge on an electron is 1.6×10−191.6 \times 10^{-19} C. How many electrons are required to accumulate a charge of one coulomb?
  3. Solved Ex.10.3
    Calculate and compare the electrostatic and gravitational forces between two protons which are 10−1510^{-15} m apart. Value of G=6.674×10−11G = 6.674 \times 10^{-11} m3^{3} kg−1^{-1} s−2^{-2} and mass of the proton is 1.67×10−271.67 \times 10^{-27} kg
  4. Solved Ex.10.4
    Three charges of 2μ\muC, 3μ\muC and 4μ\muC are placed at points A, B and C respectively, as shown in Fig. a. Determine the force on A due to other charges.
  5. Solved Ex.10.5
    Gap between two electrodes of the spark-plug used in an automobile engine is 1.25 mm. If the potential of 20 V is applied across the gap, what will be the magnitude of electric field between the electrodes?
  6. Solved Ex.10.6
    Three point charges are placed at the vertices of a right isosceles triangle as shown in the Fig. a. What is the magnitude and direction of the resultant electric field at point P which is the mid point of its hypotenuse?
  7. Solved Ex.10.7
    A simplified model of hydrogen atom consists of an electron revolving about a proton at a distance of 5.3×10−115.3 \times 10^{-11}m. The charge on a proton is +1.6×10−19+1.6 \times 10^{-19} C. Calculate the intensity of the electric field due to proton at this distance.
  8. Solved Ex.10.8
    A charge of 5.0 C is kept at the centre of a sphere of radius 1 m. What is the flux passing through the sphere? How will this value change if the radius of the sphere is doubled?
  9. Solved Ex.10.9
    An electric dipole of length 2.0 cm is placed with its axis making an angle of 30∘30^{\circ} with a uniform electric field of 10510^{5} N/C. as shown in figure. If it experiences a torque of 10310\sqrt{3} Nm, calculate the magnitude of charge on the dipole.

Exercises

23 q

Choose the correct option

Practice · 7
  1. Choose the correct option.
    Ex Q.1 (i)
    A positively charged glass rod is brought close to a metallic rod isolated from ground. The charge on the side of the metallic rod away from the glass rod will be
    1. A.
      same as that on the glass rod and equal in quantity
    2. B.
      opposite to that on the glass of and equal in quantity
    3. C.
      same as that on the glass rod but lesser in quantity
    4. D.
      same as that on the glass rod but more in quantity
  2. Ex Q.1 (ii)
    An electron is placed between two parallel plates connected to a battery. If the battery is switched on, the electron will
    1. A.
      be attracted to the +ve plate
    2. B.
      be attracted to the -ve plate
    3. C.
      remain stationary
    4. D.
      will move parallel to the plates
  3. Ex Q.1 (iii)
    A charge of +7 μ+ 7\ \muC is placed at the centre of two concentric spheres with radius 2.0 cm and 4.0 cm respectively. The ratio of the flux through them will be
    1. A.
      1:4
    2. B.
      1:2
    3. C.
      1:1
    4. D.
      1:16
  4. Ex Q.1 (iv)
    Two charges of 1.0 C each are placed one meter apart in free space. The force between them will be
    1. A.
      1.0 N
    2. B.
      9×1099 \times 10^{9} N
    3. C.
      9×10−99 \times 10^{-9} N
    4. D.
      10 N
  5. Ex Q.1 (vi)
    A metallic sphere A isolated from ground is charged to +50 μ+50\ \muC. This sphere is brought in contact with other isolated metallic sphere B of half the radius of sphere A. The charge on the two sphere will be now in the ratio
    1. A.
      1:2
    2. B.
      2:1
    3. C.
      4:1
    4. D.
      1:1
  6. Ex Q.1 (vii)
    Which of the following produces uniform electric field?
    1. A.
      point charge
    2. B.
      linear charge
    3. C.
      two parallel plates
    4. D.
      charge distributed an circular any
  7. Ex Q.1 (viii)
    Two point charges of A=+5.0 μA = +5.0\ \muC and B=−5.0 μB = -5.0\ \muC are separated by 5.0 cm. A point charge C=1.0 μC = 1.0\ \muC is placed at 3.0 cm away from the centre on the perpendicular bisector of the line joining the two point charges. The charge at C will experience a force directed towards
    1. A.
      point A
    2. B.
      point B
    3. C.
      a direction parallel to line AB
    4. D.
      a direction along the perpendicular bisector

Answer the following questions

Practice · 9
  1. Answer the following questions.
    Ex Q.2 (i)
    What is the magnitude of charge on an electron?
  2. Ex Q.2 (ii)
    State the law of conservation of charge.
  3. Ex Q.2 (iii)
    Define a unit charge.
  4. Ex Q.2 (iv)
    Two parallel plates have a potential difference of 10V between them. If the plates are 0.5 mm apart, what will be the strength of electric charge.
  5. Ex Q.2 (v)
    What is uniform electric field?
  6. Ex Q.2 (vi)
    If two lines of force intersect of one point. What does it mean?
  7. Ex Q.2 (vii)
    State the units of linear charge density.
  8. Ex Q.2 (viii)
    What is the unit of dipole moment?
  9. Ex Q.2 (ix)
    What is relative permittivity?

Solve numerical examples

Practice · 7
  1. Solve numerical examples. Take 14πε0=9×109\dfrac{1}{4\pi\varepsilon_{0}} = 9 \times 10^{9} N m2^{2}/C2^{2} and ε0=8.85×10−12\varepsilon_{0} = 8.85 \times 10^{-12} C2^{2}/N m2^{2}, the values stated in Sec. 10.4.3 of this chapter. (The book's Exercises print no constants preamble; these are supplied so that each question can be attempted on its own.)
    Ex Q.3 (i)
    Two small spheres 18 cm apart have equal negative charges and repel each other with the force of 6×10−36 \times 10^{-3} N. Find the total charge on both spheres.
  2. Ex Q.3 (ii)
    A charge +q exerts a force of magnitude -0.2 N on another charge -2q. If they are separated by 25.0 cm, determine the value of q.
  3. Ex Q.3 (iii)
    Four charges of +6×10−8+ 6 \times 10^{-8} C each are placed at the corners of a square whose sides a are 3 cm each. Calculate the resultant force on each charge and show its direction on a digram drawn to scale.
  4. Ex Q.3 (iv)
    The electric field in a region is given by E⃗=5.0\vec{E} = 5.0 kN/C. Calculate the electric flux Through a square of side 10.0 cm in the following cases (a) the square is along the XY plane (b) The square is along XZ plane (c) The normal to the square makes an angle of 45045^{0} with the Z axis.
  5. Ex Q.3 (v)
    Three equal charges of 10×10−810 \times 10^{-8} C respectively, each located at the corners of a right triangle whose sides are 15 cm, 20 cm and 25 cm respectively. Find the force exerted on the charge located at the 90∘90^{\circ} angle.
  6. Ex Q.3 (vi)
    A potential difference of 5000 volt is applied between two parallel plates 5 cm a part a small oil drop having a charge of 9.6×10−199.6 \times 10^{-19} C falls between the plates. Find (a) electric field intensity between the plates and (b) the force on the oil drop.
  7. Ex Q.3 (vii)
    Calculate the electric field due to a charge of −8.0×10−8-8.0 \times 10^{-8} C at a distance of 5.0 cm from it.