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Solved problems for the chapter:

Transformer

View the theory »

Transformer

1. Voltage transformer

2. Power conversion - transformer efficiency

3. Current transformer

4. Forum

↓ Show theory [1] ↓

Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:transformer/3650/

Example 1.

What is an advantage of transmitting electricity at a high voltage?

It is safer.
Less equipment is needed.
It is faster.
Less energy is wasted.

Example 2.

The diagram below represents the transition of electricity from a power station to homes that are many kilometres away. Two transformers are labelled X and Y.

What type of transformers are X and Y?

	X	Y
A	step-up transformer	step-up transformer
B	step-up transformer	step-down transformer
C	step-down transformer	step-up transformer
D	step-down transformer	step-down transformer

A student makes four different types of transformers. She counts the number of turns on the primary and secondary coils. She labels each transformer as either step-up or step-down. Which row shows the correct labels?

	number of turns on the primary coil	number of turns on the secondary coil	step-up or step-down transformer
A	5	5	step-up
B	20	10	step-down
C	10	5	step-up
D	10	20	step-down

How is electricity transmitted over large distances and why is it transmitted in this way?

	how	why
A	at high voltage	to reduce energy loss
B	at high voltage	for safety
C	at low voltage	to reduce energy loss
D	at low voltage	for safety

Which statement about a transformer is correct?

An alternating current in the iron core induces an alternating current in the secondary coil.
An alternating current in the primary coil induces a direct current in the secondary coil.
An alternating current in the primary coil induces an alternating voltage across the secondary coil.
There is an alternating current in the iron core from the primary coil to the secondary coil.

The diagram represents a transformer. Which row shows materials suitable for making the core and the primary coil?

	core	primary coil
A	steel	copper
B	iron	copper
C	steel	plastic
D	iron	plastic

Transformers are used in the transmission of electrical power to houses. Which type of transformer is used at the power station prior to connection to the power lines and which type is used prior to delivery to the houses?

	power station	before houses
A	step-down	step-up
B	step-up	step-up
C	step-down	step-down
D	step-up	step-down

Which metal is used for the core of a transformer?

copper
aluminium
steel
soft iron

Electrical power is transmitted from power stations to houses using the National Grid. In which part of the National Grid is the voltage highest?

10.

The step-down transformer shown reduces mains voltage to 12 V. When the transformer is used, some energy is transferred to the surroundings. Which type of energy is transferred to the surroundings?

thermal energy
elastic energy
light energy
chemical energy

11.

A step-up transformer produces a a.c. output from a a.c. input. There are turns on the secondary coil. How many turns are there on the primary coil?

12.

The diagram shows a transformer connected to a a.c. supply. What is the potential difference across the secondary coil of the transformer?

13.

A step-down transformer is percent efficient. It has an input voltage of a.c. and an output voltage of a.c. The current in the primary coil is . What is the current in the secondary coil?

14.

An electrical device changes the voltage of an electrical supply from a.c. to a.c. What is this device?

a transformer
a voltmeter
a relay
a generator

15.

A battery charger is plugged into a a.c. supply. The charger is used to charge a d.c. battery. The charger contains a transformer. What is the purpose of the transformer?

rectify the a.c.
steps down the voltage
rectify the d.c.
steps up the voltage

16.

From which materials are the coil and the core of a transformer made?

	coil	core
A	soft iron	copper
B	copper	steel
C	copper	soft iron
D	steel	soft iron

17.

A simple transformer has an input of and an output of . There are turns on the primary coil. How many turns are there on the secondary coil?

18.

A step-up transformer is used before electricity is transmitted by overhead cables. Which statement explains why the step-up transformer is used?

It increases the current to reduce energy loss in the cables.
It increases the voltage to increase the speed at which the electricity travels.
It increases the current to increase the speed at which the electricity travels.
It increases the voltage to reduce energy loss in the cables.

19.

A transformer has an input voltage of . The primary coil has turns and the secondary coil has turns. What is the output voltage?

20.

A transformer has turns on its primary coil and turns on its secondary coil. What input voltage is needed to give an output voltage of ?