An earthed magnet is near a bar of material which is seen to be repelled by the magnet.
What could the bar of material be?
[The system is isolated and no currents are induced.]
A. A bar of unmagnetised soft iron.
B. A bar of unmagnetised cobalt.
C. A bar of electrostatically charged copper.
D. A bar of magnetised steel.
E. A bar of electrostatically charged aluminium.
We must first ask ourselves: what could be the reasons the bar repels the magnet?
The most probable and obvious answer is that the bar could in itself be magnetized.
With this theory in mind, we can simply rule out which of the materials within the answers are not magnetised.
A, B are unmagnetised.
C, E are electrostatically charged, relating to static energy, and are therefore irrelevant.
Hence the answer being D.