Moving Charges and Magnetism - Result Question 23
23. A beam of electrons is moving with constant velocity in a region having simultaneous perpendicular electric and magnetic fields of strength $20 Vm^{-1}$ and $0.5 T$ respectively at right angles to the direction of motion of the electrons. Then the velocity of electrons must be
[1996]
(a) $8 m / s$
(b) $20 m / s$
(c) $40 m / s$
(d) $\frac{1}{40} m / s$
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Answer:
Correct Answer: 23. (c)
Solution:
- (c) The electron moves with constant velocity without deflection. Hence, force due to magnetic field is equal and opposite to force due to electric field.
$q v B=q E \Rightarrow v=\frac{E}{B}=\frac{20}{0.5}=40 m / s$
