Question

A circular conducting disc is rotating at an angular velocity $\omega$ about an axis perpendicular to plane passing through center of disc. Then,

• A. Potential difference between center and circumference of disc is not zero
• B. Potential difference between center and circumference of disc is zero
• C. If a magnetic field perpendicular to the plane of disc is switched on, $\omega$ may increase.
• D. If a magnetic field perpendicular to plane of disc is switched on, $\omega$ may decrease.

Answer 1

Answer: (A), (C), (D)

The correct options are
A Potential difference between center and circumference of disc is not zero
C If a magnetic field perpendicular to the plane of disc is switched on, $\omega$ may increase.
D If a magnetic field perpendicular to plane of disc is switched on, $\omega$ may decrease.

Due to centrifugal force electrons are at circumference
If B is switched on suddenly, the induced field is generated which may be in the direction of 'I' or in direction opposite to 'I', so $\omega$ may increase or decrease.