A bar magnet falls freely from a height of 9.8 m through a metal ring. Its acceleration will be equal to
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → less than \( 9.8\,\mathrm{m\,s^{-2}} \)
As the magnet falls through the ring, the flux linked with the ring changes and an emf and a current are induced in it. By Lenz’s law the induced current acts to oppose the motion that causes it.
So the ring exerts an upward magnetic force on the falling magnet, in addition to its weight acting downwards:
\( ma = mg - F_{\mathrm{magnetic}} \Rightarrow a = g - \frac{F_{\mathrm{magnetic}}}{m} \lt g \)
The acceleration is therefore less than \( 9.8\,\mathrm{m\,s^{-2}} \).