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JAMB Physics 2020 past questions and answers

2 questions. Try each one, then open the answer to check yourself and read the explanation.

Question 8

Current Electricity

The effect of closing the key K in the circuit shown in Fig. 1 would be to

Diagram for this question
  1. A.increase the current by 0.4A.
  2. B.reduce the current by 0.4A
  3. C.increase the current by 0.6A.
  4. D.reduce the current by 0.6A.
Show the answer and explanation

Answer: A (increase the current by 0.4A.)

Explanation

With K open: R = 8 + 2 = 10 Ω, I = 6 ÷ 10 = 0.6 A. With K closed the two 8 Ω resistors are in parallel (4 Ω): R = 6 Ω, I = 1 A. The current rises by 0.4 A.

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Question 37

Electrical Energy and Power

Which of the following instruments consumes the highest current?
Electric iron: 250V, 1kW
Television set: 220V, 110W
Torch light: 6V, 30W
Immersion heater: 110V, 500W

  1. A.Electric iron
  2. B.Television set
  3. C.Torch light
  4. D.Immersion heater
Show the answer and explanation

Answer: C (Torch light)

Explanation

I = P/V: iron 1000 ÷ 250 = 4 A; TV 110 ÷ 220 = 0.5 A; torch 30 ÷ 6 = 5 A; heater 500 ÷ 110 ≈ 4.55 A. The torch light takes the most current.

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