Electromagnetism

This question is about magnetic fields.

Fig. 11.1 shows a diagram of a measuring instrument.

Fig. 11.1

Name this measuring instrument.

What information does the instrument in Fig. 11.1 give us about the core of the Earth?

Describe how you can use iron filings to show the shape of the magnetic field pattern around wire B.

Draw the shape and direction of the magnetic field pattern around wire B on Fig. 11.2.

Solenoids can be used to produce magnetic fields.

Fig. 11.3 shows the current and the number of turns of wire in four different solenoids A, B, C and D.

Fig. 11.3

The solenoids are all made of the same material using wires of equal thickness.

Which solenoid has the strongest magnetic field?

Give a reason for your answer.

This question is about magnetism.

Fig. 15.1 shows a dipping compass.

Fig. 15.1

In some places, a dipping compass shows a dip angle of 90°.

Where could the dipping compass be on Earth?

Tick (✓) two boxes.

A student uses a coil of insulated wire to construct an electromagnet.

The student uses plotting compasses to show the magnetic field around the electromagnet.

Fig. 15.2 shows a diagram of the electromagnet. The circles show the position of three plotting compasses when the electromagnet is switched on.

Fig. 15.2

Complete Fig. 15.2 by drawing arrows on the plotting compasses to show the direction they point.

One is already drawn for you.

The student uses the electromagnet to pick up some iron nails.

Fig. 15.3 shows what happens when the electromagnet is switched on.

Fig. 15.3

Explain why a chain of iron nails is attracted to the electromagnet.

You can label Fig. 15.3 to help explain your answer.

The student then places some insulated wire in a straight line between the poles of a U-shaped magnet as shown in Fig. 15.4.

Fig. 15.4

Explain what happens when a current passes through the insulated wire.

The magnetic flux density between the poles of the U-shaped magnet is 0.12 T. The length of wire that lies between the poles is 0.04 m.

Calculate the force on this length of wire when a current of 0.25 A flows through it.

Use the Equation Sheet.

Give your answer in mN.

14* An electromagnet can be made from a coil of wire and a soft iron core.

A student investigates how the strength of an electromagnet varies with the number of turns.

Fig. 14.1 shows the electromagnet and Fig. 14.2 shows a graph of the results.

Fig. 14.1
Fig. 14.2

Describe how the experiment is done using Fig. 14.1.

Explain what the graph in Fig. 14.2 tells us.

A magnetic field is produced around a current-carrying wire.

A student views the magnetic field from above, as shown by the eye in the diagram.

Which diagram shows the magnetic field around the wire?

A magnetic field is produced around a current-carrying wire.

A student views the magnetic field from above, as shown by the eye in the diagram.

Which diagram shows the magnetic field around the wire?

A teacher shows her class some magnets.

Fig. 12.1 shows the magnetic field around a bar magnet.

What is the direction of the magnetic field at X ?

Draw an arrow on the diagram in Fig. 12.1 to show your answer.

Where is the magnetic field strongest around the bar magnet?

A compass points towards ‘magnetic north’.

What does this tell us about the Earth?

The teacher wraps a coil of insulated wire around a soft iron core as shown in Fig. 12.2.

Describe what the student needs to do to create a magnetic field.

The student changes the number of turns in the coil. He records the number of steel pins that the magnetic field can pick up.

The student concludes ‘The more turns, the stronger the magnetic field’.

Explain if his conclusion is true. Use the results in the table in your answer.

The student concludes ‘The more turns, the stronger the magnetic field’.

Do the results in the table support his conclusion?

Explain your answer.

The electromagnets with 20 and 40 turns pick up the same number of pins.

Suggest why the electromagnet with 40 turns is more useful.

Fig. 13.2 shows the inside of a simple d.c. motor. The direction of the current in the coil is

Which direction will the coil rotate in Fig. 13.2 ?

State the name of the rule you used to work out your answer.

A solenoid can be used to produce a magnetic field.

Which of the following increases the magnetic field strength produced?

A Decreasing the current

B Decreasing the number of turns

C Increasing the current

D Removing magnetic material from the core

Four compasses are each placed near to a wire at points A, B, C and D. Each wire has a current flowing through it. The distance of each compass from its wire is shown.

Which compass experiences the greatest magnetic field strength?