Effects of 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.

The diagram shows a transformer. The input voltage is 240V. What is the output voltage?

• 6.0 V

• 12 V

• 20 V

• 40 V

A coil carries a current in a magnetic field. The coil experiences a turning effect. Which device uses this effect?

• DC Motor

• Transformer

• Relay

• Electromagnet

A magnet is suspended from a spring so that it can move freely inside a stationary coil. The coil is connected to a sensitive centre-zero galvanometer. The magnet repeatedly moves slowly up and down. What does the galvanometer show?

• a constantly changing reading

• a steady reading to the left

• a steady reading to the right

• a steady reading of zero

An e.m.f. is induced across a wire when it moves through the magnetic field between the poles of a magnet. Which electrical device operates because of this effect?

• Battery

• Cathode ray tube

• Generator

• Motor

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 transformer has 1000 turns on its primary coil. An input voltage of 12V is applied to the primary coil, and an output voltage of 120V is induced across the secondary coil. How many turns are on the secondary coil of the transformer?

• 100

• 120

• 1000

• 10 000

Which diagram represents the voltage output of a simple a.c. generator?

• 
• 
• 
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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.

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