Sec 4 Physics Magnetism topical questions

Name two magnetic materials and two non-magnetic materials.

State the law of magnetism.

State two properties of magnetic field lines.

Distinguish between soft iron and steel as magnetic materials.

State one method of demagnetising a magnetised steel bar.

The north pole of a bar magnet is brought near each end, in turn, of a freely hanging iron nail that was originally unmagnetised.

1. (a)State and explain what is observed when the magnet approaches either end of the nail.[3]
2. (b)Name the pole induced at the end of the nail nearest the magnet’s north pole, and at the far end.[2]
3. (c)State what happens to the nail’s magnetism after the magnet is taken away, if the nail is made of soft iron.[1]

A student is given two identical-looking steel rods, X and Y, and a thread for suspension. Rod X is known to be a magnet; rod Y may be a magnet or an unmagnetised steel rod.

1. (a)Describe how to use rod X to decide whether Y is magnetised.[3]
2. (b)State the observation that proves Y is magnetised, and explain why the opposite observation proves nothing.[3]

A technician magnetises a steel knitting needle by the electrical method, using a solenoid, a battery and a switch.

1. (a)Describe what the technician does.[2]
2. (b)State how the poles of the needle are decided.[2]
3. (c)Explain why steel, not soft iron, is the right material for a needle that must stay magnetised.[1]

A plotting compass is moved slowly along a line from the north pole of a bar magnet to its south pole, passing first around the outside of the magnet.

1. (a)Describe how the compass reading changes along the journey.[3]
2. (b)Sketch in words the complete field-line pattern this traces out.[2]

Two identical bar magnets are placed on a table with their north poles facing each other 5 cm apart. A plotting compass is slid along the straight line between the two poles.

1. (a)Describe and explain the compass behaviour at the midpoint of the line.[3]
2. (b)Describe the compass behaviour just outside the midpoint towards one magnet, and name the region.[2]
3. (c)State what changes if one magnet is turned so a north pole faces a south pole.[2]

A ship’s steel locker contains a strong magnet lying loose near a spare steel compass needle and a soft-iron pin.

1. (a)Explain what happens to the pin and the needle while they lie near the magnet.[3]
2. (b)After the locker is emptied, the needle is found to still attract the pin but the pin no longer attracts anything. Explain the different outcomes.[4]

A student must demagnetise a steel ruler using a solenoid connected to a low-voltage alternating-current supply, and then check that the method worked.

1. (a)Describe the demagnetising procedure, including the precaution that makes it work.[3]
2. (b)Explain why the alternating supply, and not a battery, is essential.[2]
3. (c)Describe a check that confirms the ruler is demagnetised.[2]

A recycling plant feeds mixed rubbish along a conveyor belt. Suspended above the end of the belt is a powerful electromagnet with a soft-iron core, whose current can be switched. The rubbish contains steel cans, aluminium cans, paper and glass.

1. (a)Explain, with reasons, which materials the electromagnet separates and which it leaves behind.[4]
2. (b)Explain why the core is soft iron rather than steel.[2]
3. (c)The steel cans drop into a bin when the current is switched off. Explain why they fall.[2]