Home Learning Quiz - Magnetism

1. The diagram shows a magnet being used to pick up a steel needle. The north pole of the magnet is close to the centre Y of the needle. What is the polarity induced in the needle at X? (Write your answer as North or South).

The north pole of the magnet induces a north polarity in the steel needle at point X. This is because opposite poles attract each other, so the north pole of the magnet attracts the south pole of the needle, causing the north pole of the needle to be induced at point X.

Explanation

The north pole of the magnet induces a north polarity in the steel needle at point X. This is because opposite poles attract each other, so the north pole of the magnet attracts the south pole of the needle, causing the north pole of the needle to be induced at point X.

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2. It can be deduced that a piece of metal is already a magnet if

Copper wire is attracted to it

Both ends of a compass needle are attracted to it

A magnet is attracted to it

One end of a compass needle is repelled by it

Repulsion is the only TRUE test of a magnet.

Explanation

Repulsion is the only TRUE test of a magnet.

3. Which of the following is the best way to demagnetise a magnetised steel needle?

Break it into two pieces.

Leave it next to another strong magnet.

Leave it inside a solenoid carrying direct current.

Slowly pull it out of a solenoid carrying alternating current.

Slowly pulling a magnetized steel needle out of a solenoid carrying alternating current can demagnetize it. This is because the changing magnetic field produced by the alternating current induces a current in the needle, which creates a magnetic field opposite to the original magnetization. As the needle is slowly pulled out, the opposing magnetic fields gradually cancel each other out, resulting in demagnetization. Breaking it into two pieces or leaving it next to another strong magnet will not necessarily demagnetize it, and leaving it inside a solenoid carrying direct current may not have the same demagnetizing effect as alternating current.

Explanation

Slowly pulling a magnetized steel needle out of a solenoid carrying alternating current can demagnetize it. This is because the changing magnetic field produced by the alternating current induces a current in the needle, which creates a magnetic field opposite to the original magnetization. As the needle is slowly pulled out, the opposing magnetic fields gradually cancel each other out, resulting in demagnetization. Breaking it into two pieces or leaving it next to another strong magnet will not necessarily demagnetize it, and leaving it inside a solenoid carrying direct current may not have the same demagnetizing effect as alternating current.

4. A metal bar PQ hung by a thin thread always comes to rest with end P pointing North. Another bar XY of the same metal settles in no definite direction. What happens if the two bars are brought near one another?

End P repels X but attracts end Y.

End P neither attracts nor repels end X.

End P attracts end X but end Q repels end Y.

End P and end Q both attract end X.

When the two metal bars are brought near one another, the bar PQ with end P pointing North will attract the end X of the other bar XY. This is because opposite poles attract each other, and since end P of bar PQ is pointing North, it acts as a North pole and attracts the end X of bar XY. Additionally, end Q of bar PQ will also attract end X of bar XY, as both ends Q and X have opposite polarities. Therefore, the correct answer is that end P and end Q both attract end X.

Explanation

When the two metal bars are brought near one another, the bar PQ with end P pointing North will attract the end X of the other bar XY. This is because opposite poles attract each other, and since end P of bar PQ is pointing North, it acts as a North pole and attracts the end X of bar XY. Additionally, end Q of bar PQ will also attract end X of bar XY, as both ends Q and X have opposite polarities. Therefore, the correct answer is that end P and end Q both attract end X.

5. Which of these statements about magnetic induction is correct?

Induced magnetism is always permanent.

Magnetic induction explains why unmagnetised material may be attracted by a magnet.

The material must be in contact with the magnet to be induced.

Magnetism can be induced in any material.

Magnetic induction is the process by which a magnetic field is created in a material due to the presence of a magnetic field from another source. When an unmagnetized material is brought near a magnet, the magnetic field of the magnet induces a temporary magnetism in the material, causing it to be attracted to the magnet. This temporary magnetism disappears once the material is no longer in the presence of the magnet. Therefore, the statement "Magnetic induction explains why unmagnetised material may be attracted by a magnet" is correct.

Explanation

Magnetic induction is the process by which a magnetic field is created in a material due to the presence of a magnetic field from another source. When an unmagnetized material is brought near a magnet, the magnetic field of the magnet induces a temporary magnetism in the material, causing it to be attracted to the magnet. This temporary magnetism disappears once the material is no longer in the presence of the magnet. Therefore, the statement "Magnetic induction explains why unmagnetised material may be attracted by a magnet" is correct.

6. A small bar magnet is placed in the region of a magnetic field as shown. If allowed to move freely, the magnet will

Move to the left

Move to the right

Turn clockwise

Turn anticlockwise

The N-pole is the place where the magnetic field will come forth.

Explanation

The N-pole is the place where the magnetic field will come forth.

7. Which of the following could be used for the needle of a plotting compass?

Aluminium

Copper

Iron

Steel

Steel could be used for the needle of a plotting compass because it is a magnetic material. The needle of a compass is a magnet that aligns itself with the Earth's magnetic field, allowing it to point towards the North Pole. Steel contains iron, which is highly magnetic, making it a suitable material for the needle. Aluminium and copper are not magnetic, so they would not work for the needle.

Explanation

Steel could be used for the needle of a plotting compass because it is a magnetic material. The needle of a compass is a magnet that aligns itself with the Earth's magnetic field, allowing it to point towards the North Pole. Steel contains iron, which is highly magnetic, making it a suitable material for the needle. Aluminium and copper are not magnetic, so they would not work for the needle.