Question

A free electron is placed in the path of a plane electromagnetic wave. The electron will start moving

a)Along the electric field

b)Along the magnetic field

c) Along the propagation of the wave

d) In the plane containing magnetic field and propagation of the wave.

• A. Along the electric field
• B. Along the magnetic field
• C. along the direction of propagation of the wave
• D.
  In a plane containing the magnetic field and the direction of propagation

Answer 1

Answer: (A)

The force acting on the charge placed in both electric field and magnetic field is given by,

$F_q=F_{\text{electric field}}+F_{\text{magnetic field}}$

$\Rightarrow F_q=qE+qvB\sin \theta$

Since the electron is at rest.i.e, $v=0$

$\Rightarrow F_q=qE+q\times 0\times B\sin \theta =qE$

So, the only force acting on the electron is the force due to the electric field.

Therefore, the electron will start moving along the direction of the electric field.

Hence, option $\left(A\right)$ is the correct answer.