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Crossed electric and magnetic fields: velocity selector

This type of question, asked 4 times: 26 Jul 2022, 27 Jan 2024, 8 Apr 2024, 22 Jan 2025. All 4 questions below, oldest first.

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  1. Question 1

    26 Jul 2022

    107
    A velocity selector consists of electric field E→=Ek^\overrightarrow{E}= E\widehat{k} and magnetic field B→=Bj^\overrightarrow{B}= B\widehat{j} with B=12mTB = 12mT. The value EE required for an electron of energy 728eV728eV moving along the positive xx-axis to pass undeflected is : (Given, mass of electron =9.1×10−31 kg= 9.1 \times10^{- 31}\text{ }kg )

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  2. Question 2

    27 Jan 2024

    4
    A proton moving with a constant velocity passes through a region of space without any change in its velocity. If E→\overrightarrow{E} and B→\overrightarrow{B} represent the electric and magnetic fields respectively, then the region of space may have: (A) E=0, B=0E = 0,\text{ }B = 0 (B) E=0, B≠0E = 0,\text{ }B \neq 0 (C) E≠0, B=0E \neq 0,\text{ }B = 0 (D) E≠0, B≠0E \neq 0,\text{ }B \neq 0 Choose the most appropriate answer from the options given below:

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  3. Question 3

    8 Apr 2024

    22
    An electron with kinetic energy 5eV5eV enters a region of uniform magnetic field of 3μT3\mu T perpendicular to its direction. An electric field EE is applied perpendicular to the direction of velocity and magnetic field. The value of E, so that electron moves along the same path, is ________ NC−1NC^{- 1}. (Given, mass of electron =9×10−31 kg= 9 \times10^{- 31}\text{ }kg, electric charge =1.6×10−19C= 1.6 \times10^{- 19}C )

  4. Question 4

    22 Jan 2025

    96
    A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of 2×105 ms−12 \times10^{5}{\text{ }ms}^{- 1}. When the electric field is switched off, the proton moves along a circular path of radius 2 cm . The magnitude of electric field is x×104 N/Cx \times10^{4}\text{ }N/C. the value of x is ______\_\_\_\_\_\_ Take the mass of the proton =1.6×10−27 kg= 1.6 \times10^{- 27}\text{ }kg.