Electromagnetic Effects 2

Which statement is true for an electrical transformer ?
1. It will only work if a.c. is used
2. It will work with either a.c. or d.c.
3. It is always used to increase voltage
4. It should give out more energy than it receives
Why does a transformer have a core made of iron?
1. Iron has a high melting point.
2. Iron is a conductor of electricity.
3. Iron is a conductor of heat.
4. Iron is a magnetic material.
What is reduced by a step-down transformer?
1. Current
2. Energy
3. Power
4. Voltage
Which material are used for the coils and cores of a transformer?
1. Coils: copper; Core: iron
2. Coils: copper; Core: steel
3. Coils: iron; Core: iron
4. Coils: iron; Core: steel
The diagram shows a 12 V, 3 A lamp being operated by a transformer using a 240 V supply.

If the transformer is 100% efficient, what current will flow from the supply?
1. 0.013 A
2. 0.15 A
3. 3.0 A
4. 12 A
A transformer is needed to convert a main 240 V supply into a 12 V supply.

If there are 2 000 turns on the coil on the primary coil, how many turns should there be on the secondary coil?
1. 100
2. 120
3. 20
4. 24 000
When a magnet was moved into the coil of wire shown in the diagram, there was a small reading on the sensitive meter.

Which change would, on its own, increase the size of the reading?
1. Pushing in the S-pole
2. Moving the magnet faster
3. Pulling the magnet out
4. Unwinding some of the turns of wire
Electrical energy is usually transmitted at high voltage because the ........................
1. transmission system does not require transformer
2. tranamission cables waste as little energy as possible
3. transmission cables are safer to handle
4. transmitted current is as large as possible
One of the following should not be connected to an a.c. supply.

Which one is it?
1. Power drill
2. Electric kettle
3. Moving coil meter
4. Filament lamp
Below is a diagram that shows the a uniform magnetic field.

A metal bar is swinging back and forth across as shown. An induced e.m.f. produced in the bar by the motion. One of the following shows the e.m.f. produced during one complete to-and-fro oscillation starting at 0.
Which is it?
1. A
2. B
3. C
4. D
What is the purpose of a step-down transformer?
1. To make the input current the same as the poutput curent.
2. To make the output current lower than the inpu current.
3. To make the output voltage the same as the input voltage.
4. To make the output voltage lower than the input voltage.
Below is a graph that shows the voltage of a simple a.c. dynamo with respect to time. If the speed of the rotation is halved, which one of the following A - D shows the variation of the voltage with respect to time?
1. A
2. B
3. C
4. D
Below is a diagram that shows a coil connectd to a cathode ray oscilloscope.

Nearby is a magnet on a shaft rotating slowly. An induced voltage is indicated by the oscilloscope.
One of the following A - D will not increase the induced voltage.
Which one is it?
1. Use a coil with more turns.
2. Turn the magnet in the opposite direction at the same speed.
3. Use a stronger magnet.
4. Move the magnet closer to the coil.
Transformer are used in power distribution networks as shown.
What does the step-up transformer do?
1. It make the input voltage higher than the output voltage.
2. It makes the output current higher than the input current.
3. It makes the output voltage higher than the input voltage.
4. It makes the output voltage the same as the input voltage.
An alternating current is passed through a wire stretched between the poles of a magnet.
Which way will the wire move?
1. left and right
2. right only
3. up and down
4. up only
X and Y are wires carrying electric currents at right angles to the page. P, Q and R are plotting compasses.

Any effect of the Earth's magnetic field has been ignored.

What is true about the direction and size of the currents?
direction of currents size of currents
A same larger in X than in Y
B same smaller in X than in Y
C different larger in X than in Y
D different smaller in X than in Y
1. A
2. B
3. C
4. D
A girl turns the handle of a small a.c. generator four times each second.

The generator produces a maximum output voltage of 0.5 V.

Which of the following graphs best shows this?
Which statement about the action of a transformer is correct?
1. An e.m.f. is induced in the secondary coil when an alternating voltage is applied to the primary coil.
2. An e.m.f. is induced in the secondary coil when there is a steady direct current in the primary coil.
3. The current in the secondary coil is always larger than the current in the primary coil.
4. The voltage in the secondary coil is always larger than the voltage in the primary coil.
Electrical energy is transmitted at high alternating voltages.

What is not a valid reason for doing this?
1. At high voltage, a.c. is safer than d.c.
2. For a given power, there is a lower current with a higher voltage.
3. There is a smaller power loss at higher voltage and lower current.
4. The transmission lines can be thinner with a lower current.

	direction of currents	size of currents
A	same	larger in X than in Y
B	same	smaller in X than in Y
C	different	larger in X than in Y
D	different	smaller in X than in Y

Electromagnetic Effects 2

Multiple Choice Questions