The motor effect

When there is a current in a wire, there is a magnetic field around the wire.

Figure 5 shows a wire passing through a piece of card.

There is a current in the wire.

Draw two magnetic field lines on the card in Figure 5 to show the magnetic field pattern around the wire.

A student positioned a straight wire in the magnetic field between two magnets.

The wire was perpendicular to the magnetic field.

There was a current of 0.56 A in the wire.

The magnetic force on the wire was 2.1 mN.

The length of wire in the magnetic field was 0.050 m.

Calculate the magnetic flux density of the magnetic field between the magnets.

Use the Physics Equations Sheet.

Give the unit.

The student replaced the straight wire with a loop of wire.

The loop of wire was on an axle so that the loop could rotate.

The student connected the loop of wire to a battery and a switch.

Figure 6 shows the apparatus.

When the switch is closed, magnetic forces on the loop make the loop begin to rotate.

Explain how.

You should refer to side A and side B of the loop of wire in Figure 6.

Figure 6 shows two magnets and a wire.

There is a current in the wire.

A force acts on the wire in Figure 6.

What is the direction of the force on the wire?

Tick () one box.

The length of the wire in the magnetic field between the magnets is 80 mm.

The current in the wire is 4.6 A.

The force on the wire is 0.092 N.

Calculate the magnetic flux density between the magnets.

Use the Physics Equations Sheet.

Give the unit.

Figure 7 shows an electromagnet close to a permanent magnet.

The electromagnet exerts a force on the permanent magnet.

The permanent magnet exerts an equal and opposite force on the electromagnet.

Which law is this an example of?

Tick () one box.

Give two changes to the electromagnet that would increase the force exerted on the permanent magnet.

Give two changes to the electromagnet that would reverse the direction of the force exerted on the permanent magnet.

A teacher demonstrated the motor effect. Figure 5 shows the equipment used. The equipment includes a permanent magnet.

The copper rod remains stationary while the switch is open. Complete the sentence. The tendency for an object to remain stationary is

When the switch is closed the copper rod accelerates.

In which direction will the copper rod accelerate? Tick (✓) one box.

Explain one way the teacher could increase the acceleration of the copper rod.

The magnet used in the demonstration was a permanent magnet. Figure 6 shows an iron bar and a permanent magnet.

Describe how the permanent magnet could be used to test if the iron bar is also a permanent magnet.

Figure 7 shows a magnetic compass used by walkers.

Explain how a magnetic compass provides evidence that the Earth has a magnetic field.

A teacher demonstrated the motor effect. Figure 5 shows the equipment used.

Explain why there is a force on the wire when there is a current in the wire.

Explain how the direction of the force on the wire can be predicted.

Figure 6 shows a simple electric motor.

Explain one way that the motor could be changed to increase the rate at which the coil rotates.

Figure 4 shows the magnetic field pattern around a permanent magnet.

Where is the magnetic field of the magnet the strongest?

How does Figure 4 show that the strength of the magnetic field is not the same at all places?

Figure 5 shows an electromagnet being used to separate iron and steel from

non-magnetic metals.

Explain one reason why an electromagnet is used instead of a permanent magnet.

Pieces of iron and steel are attracted to the electromagnet. Name two other metals that would be attracted to the electromagnet.

The design of the electromagnet cannot be changed. Give two ways the force exerted by the electromagnet on a piece of iron or steel could be increased.

The conveyor belt that moves the pieces of metal is driven by an electric motor.

Figure 6 shows a simple electric motor.

The length of the wire AB in the magnetic field is 120 mm. There is a current of 4.0 A in the wire. The length of wire AB experiences a force of 0.36 N. Calculate the magnetic flux density between the magnets. Give the unit.

Fleming’s left-hand rule can be used to determine the direction of the force on wire AB. Complete the labels on Figure 7 to show Fleming’s left-hand rule.

A student clamped a wire between the poles of a permanent magnet. The student investigated how the force on the wire varied with the current in the wire. Figure 13 shows the equipment used.

The top pan balance was used to determine the force on the wire.

When the switch was closed the reading on the top pan balance increased. Explain why the increased reading showed that there was an upward force on the wire.

Table 3 shows the readings on the top pan balance with the switch open and with the switch closed.

Explain how the values in Table 3 can be used to determine the size of the force on the wire.

The student varied the current in the wire and calculated the force acting on the wire. Figure 14 shows the results.

The length of the wire in the magnetic field was 0.125 m Determine the magnetic flux density.

Figure 6 shows a wire in a magnetic field.

The direction of the current in the wire is shown.

There is a force on the wire due to the current in the magnetic field.

In which direction is the force on the wire?

Tick (✓) one box.

Give two ways that the direction of the force on the wire could be reversed.

The length of the wire in the magnetic field is 0.050 m

The force on the wire is 0.072 N

magnetic flux density = 360 mT

Calculate the current in the wire.

Use the Physics Equations Sheet.

Figure 7 shows a simple motor.

Explain why the coil rotates when there is a current in the coil.