Question

A charged particle moves in a gravity-free space without change in velocity. Which of the following is/are possible?
(i) `E = 0, B = 0`
(ii) `E = 0, B != 0`
(iii) `E != 0, B = 0`
(iv) `E != 0, B != 0`
A. (i), (ii)
B. (ii), (iv)
C. (ii), (iii)
D. (i), (ii), (iv)

Answer 1

Correct Answer - D
Since velocity is constant, net force `= 0`
(i) `E = 0, B = 0` i.e. `F_(e) = 0, F_(m) = 0` O.K.
(ii) `E = 0, B != 0` i.e. `F_(e) = 0`, It may be that velocity is parallel or anti-parallel to magnetic field and hence `F_(m) = 0` O.K.
(iii) `E != 0 , B = 0`, The electric will change magnitude or magnitude and direction or velocity, Not O.K.
(iv) `E != 0, B != 0`, It may be that electric field balances magnetic force. O.K.