Question
Three methods to demagnetise a magnet are suggested. The magnet is in an east-west direction.
- hitting the magnet repeatedly with a hammer
- heating the magnet until red hot
- withdrawing the magnet from a coil which has a direct current (d.c.) in it
Which methods demagnetise the magnet?
A 1, 2 and 3
B 1 and 2 only
C 1 and 3 only
D 2 and 3 only
Answer/Explanation
Ans: B
Question
A steel bar is placed in an East-West direction for it to be demagnetised. No other magnet is nearby.
Which method is not suitable?
A Hammering the bar.
B Heating the bar to a very high temperature.
C Slowly taking the bar out of a coil that carries an alternating current.
D Slowly taking the bar out of a coil that carries a direct current.
Answer/Explanation
Ans:D
Which method does not demagnetise a bar magnet?
Heat the bar magnet and place it in the east-west direction to cool.
Place the bar magnet in the east-west direction and hammer it.
Place the bar magnet in a coil connected to an a.c. supply and slowly withdraw it.
Place the bar magnet in a coil connected to a d.c. supply and slowly withdraw it.
Answer/Explanation
Ans: D
Three piles of small nails, P, Q and R, are placed on a bench below three electromagnets.
One set of nails is made of copper, one of soft iron and one of steel.
Diagram 1 shows the situation when the electromagnets are switched on.
Diagram 2 shows the situation when the electromagnets are then switched off.
Which row correctly identifies the materials from which the nails are made?
| copper | soft iron | steel |
A | P | Q | R |
B | P | R | Q |
C | Q | P | R |
D | Q | R | P |
Answer/Explanation
Ans: A
Question
A magnet is suspended by a cotton thread.
The magnet is displaced then allowed to swing freely until it comes to rest.
Why does the magnet always come to rest pointing in the same direction?
because of the interaction between the electric field of the magnet and the electric field of the Earth
because of the interaction between the electric field of the magnet and the magnetic field of the Earth
because of the interaction between the magnetic field of the magnet and the gravitational field of the Earth
because of the interaction between the magnetic field of the magnet and the magnetic field of the Earth
Answer/Explanation
Ans: D
Question
Four nails A, B, C and D are tested to find which makes the strongest permanent magnet.
One of the nails is placed against a bar magnet and the number of paper clips which the nail can support is recorded.
The bar magnet is then removed and the number of paper clips remaining attached to the nail is
recorded. Each nail is tested individually.
Which nail becomes the strongest permanent magnet?
| number of paper clips attached to the nail | |
bar magnet present | bar magnet removed | |
A | 2 | 0 |
B | 2 | 1 |
C | 4 | 3 |
D | 5 | 2 |
Answer/Explanation
Ans: C