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Quiz Chapter 6: Electricity and Magnetism

10 questions · Form 3 Science Bab 6: Electricity and Magnetism

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. Why why electricity transmitted at extremely high voltages (e.g., 132 kV to 500 kV) through the National Grid Network?

  1. To increase current speed along cables
  2. To reduce current and minimize power lost as heat ($P = I2 R$)
  3. To eliminate the need for step-down sub-stations
  4. To prevent electrical theft along high-voltage pylons
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Answer: B

Stepping up voltage reduces transmission current ($I$). Since power loss as heat in cables depends on $I2 R$, lower current dramatically reduces energy loss.

2. What is the function of the earth wire (green/yellow striped) in a 3-pin plug?

  1. To carry current from the mains supply to the appliance
  2. To complete the circuit by returning current to the sub-station
  3. To safely direct leaked electric current from a metal body to the ground
  4. To step down voltage before it reaches internal circuits
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Answer: C

The earth wire connects the metallic outer chassis of an appliance to the ground, providing a low-resistance path that safely discharges leaked current.

3. Why are iron cores in transformers laminated into thin insulated sheets rather than solid blocks?

  1. To increase resistance of primary coils
  2. To reduce energy loss caused by induced eddy currents
  3. To prevent rusting of iron
  4. To enable direct current conversion
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Answer: B

Laminating the soft iron core breaks up circulating eddy currents within the core material, significantly reducing heat energy loss.

4. Which of the following is classified as a non-renewable source of energy?

  1. Biomass
  2. Geothermal energy
  3. Coal
  4. Hydroelectric energy
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Answer: C

Coal is a fossil fuel formed over millions of years and cannot be replenished once depleted, making it non-renewable.

5. What is the power rating of an electrical appliance that draws a current of $5 A$ when connected to a $240 V$ household supply?

  1. 48 W
  2. 245 W
  3. 1200 W
  4. 2400 W
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Answer: C

Power $P = V × I = 240 V × 5 A = 1200 W$ (or $1.2 kW$).

6. If a household consumes 100 units of electricity in a month and the tariff is RM 0.20 per unit, what is the cost of electricity consumed?

  1. RM 2.00
  2. RM 20.00
  3. RM 200.00
  4. RM 50.00
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Answer: B

Cost = Energy (units) $×$ Rate = $100 × RM 0.20 = RM 20.00$.

7. Which safety device in a domestic consumer unit automatically trips to break the electrical connection during an overload or short circuit?

  1. Electric meter
  2. Miniature Circuit Breaker (MCB)
  3. Step-down transformer
  4. Neutral wire busbar
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Answer: B

MCBs are electromagnetic safety switches that trip and open the circuit when current exceeds safe operating limits.

8. An electric kettle rated at $2.0 kW$ is operated continuously for 3 hours. How many kilowatt-hours (units) of electrical energy are consumed?

  1. 0.67 kWh
  2. 5.0 kWh
  3. 6.0 kWh
  4. 600 kWh
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Answer: C

Energy (kWh) = Power (kW) $×$ Time (h) = $2.0 kW × 3 h = 6.0 kWh$.

9. Which device directly converts solar energy into electrical energy without utilizing a rotating turbine or generator?

  1. Solar collector panel
  2. Photovoltaic solar cell
  3. Solar thermal reflector
  4. Thermocouple
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Answer: B

Photovoltaic cells directly convert photon energy from sunlight into direct current (d.c.) electricity without moving mechanical parts.

10. Calculate the energy efficiency of an electric lamp that converts 100 J of electrical energy input into 75 J of light energy and 25 J of heat energy.

  1. 25%
  2. 33%
  3. 75%
  4. 100%
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Answer: C

Efficiency = $( Useful OutputTotal Input ) × 100% = ( 75 J100 J ) × 100% = 75%$.

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