Electromagnetic Forces

An electromagnet with a soft iron core is connected to a battery and an open switch. The soft iron core is just above some small soft iron nails.

• A

• B

• C

• D

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 of 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

• B

• C

• D

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.

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

The diagram shows a coil of wire connected to a voltmeter.

A student has a magnet and an unmagnetised iron rod.

How can an e.m.f. be induced across the coil?

• holding the magnet inside the coil

• holding the iron rod inside the coil

• pushing the magnet into the coil

• pushing the iron rod into the coil

This is a picture of a simple electromagnet. How can the electromagnet be made stronger?

• Add more coils of wire to the nail.
• Use a smaller battery.
• Reverse the poles of the magnet.
• Remove all the coils and the nail.

Magnetic field produced around a straight conductor due to current in it is given by

• Fleming's right hand rule

• Right hand grip rule

• Clock rule

• Fleming's left hand rule

How are electromagnets different from magnets?

• magnets can be turned on/off
• you can turn an electromagnet on/off
• magnets are more powerful
• magnets have a North and South pole

Which of the following does not influence the strentgh of electromagnet?

• Number of turns of wire

• Magnitude of current flow in the wire

• Type of core

• Material used for insulator of the wire