Question

A positively charged disk is rotated clockwise as shown in the figure. The direction of the magnetic field at point $A$ in the plane of the disk is

• A. $⨂$ into the page
• B. $\to$ towards right
• C. $\leftarrow$ towards left
• D. $⨀$ out of the page

Answer 1

The correct option is D $⨀$ out of the page

Here, when we look at the rotating disc, we can treat is as a combination of infinite circular current carrying loops i.e. infinite infinitesimal dipoles.
As per the concept, the direction of the dipole will be such that the magnetic moment will go into the page (from South to North).
The point we are concerned about is in the equatorial plane of these dipoles and the the direction of magnetic field at this point will be From North to South ( as given in the concept ) i.e. out of the page.