Question

A magnetic field is directed normally downwards through a magnetic frame as shown in the figure. On increasing the magnetic field:

• A. plate B will be positively charged
• B. plate A will be positively charged
• C. none of the plates will be positively charged
• D. all of the above

Answer 1

Answer: (A)

plate B will be positively charged

The magnetic field increasing into the plane. Hence from Lenz's Law, the direction of induced current is such that the magnetic field due to it opposes this change in flux. Hence the induced current is in anti-clockwise direction. The electrons move in opposite direction, that is, clockwise. Hence, plate A becomes negatively charged and plate B becomes positively charged.