Question

An electron is moving with a uniform speed in the X - Y plane in a straight path along the negative X direction. If a uniform magnetic field is applied parallel along the positive z-axis, the electron will :

• A. Remain unaffected
• B. Speed up along the X direction
• C. Start moving in the Y direction
• D. Start moving in a circular path in the X-Y plane

Answer 1

The correct option is D Start moving in a circular path in the X-Y plane

According to fleming’s left hand rule the electron will experience a force perpendicular to both the magnetic field and the motion of the electron. Therefore, a force will start acting on it in the negative Y direction.

Now, when the electron is deflected towards the negative Y direction, the direction of force will change to be perpendicular to the motion of the electron, the electron will again change its direction.

This will cause the electron to continuously change its direction such that it will start moving in a circular path. The magnetic force in this case will act as the centripetal force.