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IGCSE Physics6.20P Transformer power equationTopic Practice

6.20P Transformer power equation

Know and use the relationship: input power = output power for 100% efficiency

Question 3(a)(ii)

[Maximum number: 3]

Mobile phone charger X contains a transformer and is used to charge the phone's battery.

Diagram 1 shows the information on charger X.

Input voltage = 230 V
Output voltage = 5.0 V
Output current = 1.2 A

Diagram 1

Calculate the input current to charger X.

Assume that charger X is 100% efficient.

input current = ............ A

Question 4(b)(i)

[Maximum number: 1]

This question is about transformers.

A step-up transformer has an input voltage of 230 V and an input current of 4.5 A .

The output current of the transformer is 0.21 A .

State the formula linking input power and output power for a transformer that is 100% efficient.

Question 5(b)

[Maximum number: 3]

A transformer is used to charge a mobile phone.
The diagram shows a label on the transformer.
input voltage: 230 V
input current: 0.067 A
output voltage: 5.0 V
output current: 3.1 A

Show that the transformer is approximately 100% efficient.

Question 5

[Maximum number: 4]

Transformers are useful in the transmission of electricity.

Question 5(a)

(a)

The diagram shows a step-down transformer.

Question image
[ 4 ]

Question 5(a)(ii)

(i)

State the formula linking input power and output power for a transformer.

[ 1 ]

Question 5(a)(iii)

(ii)

The step-down transformer has an input voltage of 275 kV and an output voltage of 230 V.

The transformer has an output current of 95 A.

Calculate the input current to the transformer.

Assume the transformer is 100% efficient.

input current = ............ A

[ 3 ]

Question 6(b)(ii)

[Maximum number: 3]

This is a question about a nuclear fusion power station.

The diagram shows how a fusion power station could supply the National Grid in the future.

Question image

The fusion power station could supply the input coil of the step-up transformer with a current of 28 kA at a voltage of 21 kV.

The output coil of the transformer has a voltage of 330 kV.

Assume the transformer is 100% efficient.

Calculate the current in the output coil of the transformer.

current = ............ kA

Question 7(a)(iii)

[Maximum number: 5]

This question is about transformers.

The diagram shows a step-down transformer.

Question image

The table gives some data for the step-down transformer.

Table

This transformer is not 100% efficient.

The efficiency of a transformer can be calculated using the formula

 efficiency = useful output power  total input power ×100%\text { efficiency }=\frac{\text { useful output power }}{\text { total input power }} \times 100 \%

Calculate the efficiency of the transformer.

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