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Transformers and the National Grid

12th grade (Year 13 in England) · 16 questions · Common Core: NGSS.HS-PS2-5, NGSS.HS-PS3-3 · England: GCSE Physics: Magnetism and electromagnetism (transformers), GCSE Combined Science: Energy (the National Grid)

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Score/ 16

  1. Question 1

    A 100 % efficient transformer has an input of 230 V and 10 A. The output voltage is 46 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

    AnswerA

  2. Question 2

    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

  3. Question 3

    A transformer has 1000 turns on the primary coil and 2000 turns on the secondary. The input voltage is 12 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

    AnswerV

  4. Question 4

    A 100 % efficient transformer has an input of 400 V and 2 A. The output voltage is 115 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

    AnswerA

  5. Question 5

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

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

  6. Question 6

    A transformer has 500 turns on the primary coil and 1000 turns on the secondary. The input voltage is 230 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

    AnswerV

  7. Question 7

    A 100 % efficient transformer has an input of 400 V and 10 A. The output voltage is 23 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

    AnswerA

  8. Question 8

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

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

  9. Question 9

    A transformer has 100 turns on the primary coil and 500 turns on the secondary. The input voltage is 120 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

    AnswerV

  10. Question 10

    A 100 % efficient transformer has an input of 25000 V and 10 A. The output voltage is 400000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

    AnswerA

  11. Question 11

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

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

  12. Question 12

    A transformer has 2000 turns on the primary coil and 1000 turns on the secondary. The input voltage is 12 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

    AnswerV

  13. Question 13

    A 100 % efficient transformer has an input of 25000 V and 10 A. The output voltage is 400000 V. What is the output current, in A? (Vp × Ip = Vs × Is; give 2 decimal places)

    AnswerA

  14. Question 14

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

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

  15. Question 15

    A transformer has 200 turns on the primary coil and 2000 turns on the secondary. The input voltage is 400 V. What is the output voltage, in V? (Vp ÷ Vs = Np ÷ Ns)

    AnswerV

  16. Question 16

    A 100 % efficient transformer has an input of 400 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)

    AnswerA

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Answer key: Transformers and the National Grid

  1. 1. 50 A

  2. 2. D. reduces the voltage to a safer level, about 230 V in the UK

  3. 3. 24 V

  4. 4. 6.96 A

  5. 5. A. A high voltage means a low current, so less energy is lost heating the cables

  6. 6. 460 V

  7. 7. 173.91 A

  8. 8. B. They need a changing magnetic field to induce a voltage in the secondary coil

  9. 9. 600 V

  10. 10. 0.63 A

  11. 11. D. They need a changing magnetic field to induce a voltage in the secondary coil

  12. 12. 6 V

  13. 13. 0.63 A

  14. 14. A. reduces the voltage to a safer level, about 230 V in the UK

  15. 15. 4000 V

  16. 16. 43.48 A