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Quiz Chapter 3: Electricity

10 questions · Form 5 Physics Bab 3: Electricity

10 questions · plays in fullscreen

Full Question List & Answer Key

Prefer reading to quizzing? All 10 questions are listed below with the answer and explanation under each one.

1. An electric motor takes in 500 W of electrical power and delivers 400 W of mechanical output power. What is the efficiency of the motor?

  1. 80%
  2. 125%
  3. 20%
  4. 90%
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Answer: A

Efficiency = (Output Power / Input Power) × 100% = (400 W500 W) × 100% = 80%.

2. An air conditioner rated at 1.5 kW is operated for 8 hours daily. How many units (kWh) of electricity are consumed by the appliance in a 30-day month?

  1. 360 kWh
  2. 12 kWh
  3. 36 kWh
  4. 120 kWh
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Answer: A

Energy = Power (kW) × time (hours) = 1.5 kW × (8 h/day × 30 days) = 1.5 kW × 240 h = 360 kWh.

3. Three identical 10 Ω resistors are connected in SERIES to a 15 V battery. What is the potential difference across ONE of the resistors?

  1. 15 V
  2. 5 V
  3. 10 V
  4. 1.5 V
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Answer: B

Total resistance R = 10 + 10 + 10 = 30 Ω. Current I = 1530 = 0.5 A. Voltage across one resistor V = I × R_i = 0.5 A × 10 Ω = 5 V.

4. An electric heater rated 240 V, 1200 W is connected to a 240 V mains supply. What is the operating current of the heater?

  1. 5 A
  2. 0.2 A
  3. 288 A
  4. 2 A
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Answer: A

P = V × I => I = PV = 1200 W240 V = 5 A.

5. Two resistors of 6 Ω and 12 Ω are connected in PARALLEL across a 12 V power supply. What is the total current supplied by the source?

  1. 3 A
  2. 1 A
  3. 2 A
  4. 0.67 A
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Answer: A

Effective resistance 1R = 16 + 112 = 312 => R = 4 Ω. Total current I = VR = 12 V4 Ω = 3 A.

6. A current of 2.5 A flows through a bulb for 4 minutes. What total electric charge passes through the bulb?

  1. 10 C
  2. 600 C
  3. 100 C
  4. 1000 C
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Answer: B

Q = I × t = 2.5 A × (4 × 60 s) = 2.5 A × 240 s = 600 C.

7. A uniform wire of resistance 12 Ω is stretched uniformly until its length doubles while its volume remains constant. What is the new resistance of the wire?

  1. 24 Ω
  2. 48 Ω
  3. 6 Ω
  4. 12 Ω
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Answer: B

When length doubles (l' = 2l), cross-sectional area halves (A' = A2) to keep volume constant. New R' = ρ(2l / (A2)) = 4 ρ(lA) = 4 × 12 = 48 Ω.

8. Superconductors are unique materials that exhibit:

  1. Infinite resistance at room temperature
  2. Zero electrical resistance below a critical transition temperature (Tc)
  3. Zero potential difference regardless of current
  4. Constant current output under changing magnetic fields
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Answer: B

Superconductors lose all electrical resistance (R = 0) when cooled below their specific critical temperature (Tc).

9. If 120 J of electrical work is done to transfer 15 C of charge across a resistor, what is the potential difference across the resistor?

  1. 1800 V
  2. 8 V
  3. 0.125 V
  4. 105 V
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Answer: B

V = WQ = 120 J15 C = 8 V.

10. Why is electrical energy transmitted at very high voltages over long distances in national grid systems?

  1. To increase the speed of electrons in the transmission lines
  2. To minimize power loss in the cables due to heat (I²R loss)
  3. To increase the total electrical resistance of the cables
  4. To ensure high current flow into household appliances
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Answer: B

Transmitting at high voltage lowers the current (I = PV). Since power loss in cables is P_loss = I²R, lower current drastically reduces thermal energy loss.

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