| 1 | 2 | 3 | 4 | 5 | 6 |
| 7 | 8 | 9 |
Question 1
This question is about a step-down transformer. |
a) | State the name of the parts labelled A, B and C.
|
b) | State if this is a step up or a step down transformer.
|
c) | Explain the operation of the transformer above.
|
|
Question 2
The diagram below shows a transformer. |
a) | State the equation linking number of turns on each coil, input voltage and output voltage.
|
b) | The primary coil has 400 turns. Calculate how many turns are on the secondary coil if the voltage is reduced to 115 V from 230 V.
|
c) | The current in the primary coil is 2.5 A. Calculate the power dissipated in the primary coil.
|
d) | State the power output at the secondary coil if the transformer is 100% efficient.
|
|
Question 3
A step up transformer has 12,000 turns on the secondary coil. The primary coil has 450 turns. |
a) | Calculate the input voltage to the primary coil if the output voltage is 600 V.
|
b) | Give the name of a suitable metal for the core of the transformer.
|
c) | Transformers are used to increase the voltage output of power stations before distribution via the National Grid. Explain why electricity is transmitted at high voltages.
|
|
Question 4
a) | What is the purpose of a transformer? A to convert A.C. to D.C. B to decrease or increase the voltage of the alternating current C to store electric charge D to convert chemical energy to thermal energy
|
b) | What happens in a step-down transformer? A the voltage decreases and the current decreases B the voltage increases and the current increases C the voltage decreases and the current increases D the voltage increases and the current decreases
|
c) | A transformer has 600 turns on the primary coil and an input voltage of 230 V. The output voltage is 575 V. Calculate the number of turns on the secondary coil.
|
d) | Which of the following is not a use of a transformer. A mobile phone charger B increasing voltage at output of a power station C a battery powered lamp
|
|
Question 5
This question is about electricity transmission via the National Grid. |
a) | Label the diagram below to show the step up and step down transformers used in the National Grid.
|
b) | Explain why step-up transformers are used at the output of power stations.
|
c) | The output voltage of a power station is 25,000 V. Electricity is transmitted via the National Grid at 400 kV. The step up transformer has 150,000 turns on the secondary coil. Calculate the number of turns on the primary coil.
|
|
Question 6
a) | A transformer has an input voltage of 230 V and an input current of 5 A. Calculate the input power of the transformer.
|
b) | State the equation linking input power and output power for a transformer.
|
c) | The transformer has 1,500 turns on the primary coil and 120 turns on the secondary coil. Calculate the output voltage of the transformer.
|
d) | Calculate the output current of the transformer.
|
|
Question 7
The power cable for a student's laptop stops working. The manufacturer has 3 possible replacements. The data for the chargers is in the table below. |
a) | State the input voltage to the transformer from the mains supply.
|
b) | The laptop needs a 5 V supply. Use data from the table to determine which of the transformers would be a suitable replacement.
|
c) | The power at the input of the transformer is 240 W. The current at the output of the transformer is 45 A. Calculate the efficiency of the transformer.
|
d) | Explain why the output power is less than the input power.
|
|
Question 8
a) | A student is investigating how the number of turns on the secondary coil affects the output voltage. State two control variables for the student's investigation.
|
b) | The student's data is below. Plot a graph of number of secondary turns against output voltage. Model answer
|
c) | Use the graph to estimate the output voltage if there were 60 turns on the secondary coil.
|
d) | The student concluded that if she doubled the number of turns on the secondary coil, the output voltage would double. Do you agree with the students conclusion? Explain why.
|
|
Question 9
a) | Draw a labelled diagram of a transformer.
|
b) | Explain how a transformer works to increase the voltage of an alternating current input.
|
c) | A transformer has 120 turns on the primary coil and an alternating input of 15 V. Calculate the number of turns on the secondary required to increase the voltage to 90 V.
|
|
| 1 | 2 | 3 | 4 | 5 | 6 |
| 7 | 8 | 9 |