Question

An em wave is propagating in a medium with a velocity \(\overrightarrow{V} = V\hat{i}\) . The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along

• A. – z direction
• B. – y direction
• C. + z direction
• D. – x direction

Answer 1

The Correct Option is C

To solve this question, we need to use the right-hand rule from electromagnetism, which relates the directions of the electric field, magnetic field, and the propagation of an electromagnetic wave.

1. The velocity of the electromagnetic wave (\(\overrightarrow{V}\)) is given as \(\overrightarrow{V} = V\hat{i}\), which indicates that the wave is propagating in the positive x-direction.
2. The electric field vector (\(\overrightarrow{E}\)) is oscillating along the positive y-axis. Let's denote this as \(\overrightarrow{E} = E\hat{j}\).
3. According to the right-hand rule, the thumb represents the direction of wave propagation, the index finger represents the direction of the electric field, and the middle finger (perpendicular to both) represents the direction of the magnetic field (\(\overrightarrow{B}\)).
4. Applying the right-hand rule:
   • Point your thumb in the direction of \(\overrightarrow{V}\) (i.e., along the +x-axis).
   • Point your index finger in the direction of \(\overrightarrow{E}\) (i.e., along the +y-axis).
   • Your middle finger will then point into the +z direction, showing the direction of the magnetic field \(\overrightarrow{B}\).
5. Thus, the oscillating magnetic field \(\overrightarrow{B}\) is in the +z direction.

The correct option is + z direction.