electromagnetism

A strong electromagnet is used to attract pins.

What happens when the current in the coil is halved?

• No pins are attracted.

• Some pins are attracted, but not as many

• The same number of pins is attracted.

• More pins are attracted.

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NGSS.HS-PS2-5

NGSS.HS-PS3-5

A coil carries a current in a magnetic field. The coil experiences a turning effect.

Which device uses this effect?

• a d.c. motor

• an electromagnet

• a relay

• a transformer

• P, Q and R

• P and Q only

• P only

• R only

The diagram shows a flat, rectangular coil placed between the poles of a magnet.

There is a current in the coil that makes it turn in the direction shown in the diagram.

Which change would make the coil turn in the opposite direction?

• decreasing the current in the coil

• increasing the number of turns on the coil

• reversing both the direction of the current in the coil and the poles of the magnet

• reversing only the direction of the current in the coil

A current-carrying wire XY lies in the magnetic field between the two poles of a U-shaped electromagnet. A force acts on the wire XY because of the magnetic field.

Each of the following actions is carried out separately.

● The current in the wire XY is reversed.

● The magnetic field is reversed.

● Both the current in the wire XY and the magnetic field are reversed at the same time.

How many of these actions cause the direction of the force on the wire XY to be reversed?

• 0

• 1

• 2

• 3

A current-carrying coil in a magnetic field experiences a turning effect.

How can the turning effect be increased?

• Increase the number of turns on the coil.

• Reduce the size of the current.

• Reverse the direction of the magnetic field.

• Use thinner wire for the coil.

An electric current is passed through a coil of wire.

Which diagram shows the shape of the magnetic field produced in the middle of the coil?

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• 
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Which diagram shows the magnetic field pattern around a wire that is carrying a current perpendicular to the page?

• 
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A toy railway engine is driven around a track by a d.c. electric motor.

How can the speed of the motor be increased?

• Use a motor made with fewer turns of wire.

• Use a smaller d.c. voltage.

• Use a stronger magnet in the motor.

• Use the supply with its connections reversed.

The diagram shows a simple d.c. electric motor which is rotating.

Which change will make the motor rotate more quickly?

• increasing the number of turns on the coil

• removing the magnets

• reversing the battery

• reversing the polarity of the magnets