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Quiz Chapter 6: Electricity and Magnetism

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

Question 1 of 10Score: 0

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

Full Question List & Answer Key

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

1. 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.

2. On what scientific principle does an electric generator operate to produce electricity?

  1. Thermionic emission
  2. Electromagnetic induction
  3. Electrostatic discharge
  4. Photoelectric effect
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Answer: B

Generators produce electricity by moving a conductor through a magnetic field (or rotating a magnet inside a coil) via electromagnetic induction.

3. Where is a step-UP transformer placed within the National Grid Network?

  1. Between step-down sub-stations and residential homes
  2. Inside domestic consumer units
  3. Immediately after the power station generator
  4. Between high-voltage transmission lines and light industry
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Answer: C

Step-up transformers are located right at power stations to raise generated voltage (e.g. 11 kV or 25 kV) up to 132-500 kV before grid transmission.

4. 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.

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. What visual waveform appears on the screen of a Cathode Ray Oscilloscope (C.R.O.) when connected to a direct current (d.c.) voltage source with the time-base turned ON?

  1. Sinusoidal wave
  2. Square wave
  3. Straight horizontal line
  4. Vertical line
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Answer: C

Direct current flows in one direction with constant magnitude, producing a single horizontal line offset from the center on a C.R.O.

7. 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.

8. 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.

9. Which condition must be met for a transformer to step DOWN a supply voltage?

  1. Number of secondary turns ($N_s$) > Primary turns ($N_p$)
  2. Number of secondary turns ($N_s$) < Primary turns ($N_p$)
  3. Primary current ($I_p$) < Secondary current ($I_s$)
  4. Primary voltage ($V_p$) < Secondary voltage ($V_s$)
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Answer: B

A step-down transformer decreases output voltage by having fewer turns in the secondary coil than in the primary coil ($N_s < N_p$).

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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