Transformers and the National Grid

Question 1

A transformer has 500 turns on the primary coil and 2500 turns on the secondary. The input voltage is 400 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 2

A 100 % efficient transformer has an input of 25000 V and 4 A. The output voltage is 400000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 3

Why don't transformers work with a steady dc supply?

• A. They need a changing magnetic field to induce a voltage in the secondary coil
• B. dc is too dangerous
• C. The iron core melts
• D. dc has no voltage

Question 4

A transformer has 100 turns on the primary coil and 50 turns on the secondary. The input voltage is 400 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 5

A 100 % efficient transformer has an input of 230 V and 5 A. The output voltage is 46 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 6

Why does the National Grid transmit electricity at very high voltages?

• A. High voltage makes electricity travel faster
• B. It makes the cables lighter
• C. Homes need very high voltages
• D. A high voltage means a low current, so less energy is lost heating the cables

Question 7

A transformer has 2000 turns on the primary coil and 40000 turns on the secondary. The input voltage is 230 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 8

A 100 % efficient transformer has an input of 25000 V and 10 A. The output voltage is 275000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 9

What does a step-down transformer near your home do?

• A. increases the voltage for homes
• B. turns ac into dc
• C. stores electricity for the night
• D. reduces the voltage to a safer level, about 230 V in the UK

Question 10

A transformer has 200 turns on the primary coil and 800 turns on the secondary. The input voltage is 400 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 11

A 100 % efficient transformer has an input of 25000 V and 4 A. The output voltage is 400000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 12

A transformer has more turns on its secondary coil than its primary coil. What type is it?

• A. a motor
• B. step-down
• C. a generator
• D. step-up

Question 13

A transformer has 1000 turns on the primary coil and 50 turns on the secondary. The input voltage is 24 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V

Question 14

A 100 % efficient transformer has an input of 25000 V and 5 A. The output voltage is 275000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

Answer A

Question 15

A transformer has more turns on its secondary coil than its primary coil. What type is it?

• A. step-down
• B. step-up
• C. a generator
• D. a motor

Question 16

A transformer has 1000 turns on the primary coil and 10000 turns on the secondary. The input voltage is 230 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

Answer V