The motor effect

A student uses a small magnet to build an electric motor.

The magnetic field around the magnet can be shown like this:

The battery is connected to the coil of insulated wire by the metal pins.

The current is clockwise around the coil of insulated wire and part of the coil is perpendicular to the magnetic field.

State the technique used to find the direction of the force acting on the coil.

The table shows some data about the motor.

Calculate the force acting on the coil.

Use the Equation Sheet.

The student now doubles the number of coils in the motor.

They do this by using a piece of wire which is twice as long.

The battery, the wire diameter, the wire material and the coil size are unchanged.

The current in the original coil was 500 mA.

State the current in the new coil.

Explain whether the new motor turns faster, slower, or at the same speed as the original motor.

Consider the force acting on the new coil.

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.

Which diagram explains how a simple d.c. electric motor spins?

The diagram shows a wire placed in a magnetic field.

The electronic balance is used to work out the force acting on the wire.

When Switch S is open, the electronic balance reading is 0.0 g. Explain why.

When Switch S is closed, the electronic balance has a positive reading of 0.3 g.

Explain why the balance shows a reading when Switch S is closed.

State the reading on the balance if the polarity of the battery is reversed.

The polarity of the battery is unchanged from (b)(i). State the reading on the balance if the poles of the magnet are reversed.

The experiment is repeated.

• When Switch S is closed the force on the wire is 0.004 N.

• The ammeter reads 0.8 A.

• The length of the wire in the magnetic field is 0.05 m.

Calculate the magnetic flux density around the wire. Use the Data Sheet.

A student investigates if the current in the wire changes the force on the wire.

Answer the questions to describe how the student can do this investigation.

What does the student vary ?

What does the student control ?

A current-carrying wire is placed in a magnetic field.

The magnetic flux density between the poles is 0.08 T.

Calculate the force acting on the wire.

Use values from the diagram and an equation from the Data Sheet to help you.

9.6 × 10⁻⁵ N A

9.6 × 10⁻⁴ N B

9.6 × 10⁻³ N C

9.6 × 10⁻² N D

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.

Fleming’s left-hand rule is used to show the direction of the force produced when a current flows in a magnetic field.

Explain how.

A simple motor is shown in the diagram.

Use the diagram to explain how rotation is caused in the motor.

Calculate the magnetic flux density on a 0.5 m long conductor when a current of 0.8 A flows.

The force produced is 0.6 N.