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Quiz Chapter 3: Electricity

10 questions · Form 5 Physics Bab 3: Electricity

Question 1 of 10Score: 0

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

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 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.

2. 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.

3. 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.

4. Which circuit component maintains a non-linear V-I relationship (non-ohmic)?

  1. Constantan wire at constant temperature
  2. Carbon resistor
  3. Filament lamp
  4. Copper connecting wire
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Answer: C

A filament lamp gets hotter as current increases, raising its resistance and producing a non-linear (curved) V-I graph.

5. Which factor causes the terminal potential difference across a battery to be LESS than its electromotive force (e.m.f.) during closed circuit operation?

  1. Resistivity of connecting copper wires
  2. Voltage drop across the internal resistance of the battery
  3. Atmospheric pressure surrounding the circuit
  4. The capacity of the external load resistor
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Answer: B

When current I flows, a potential drop ('lost volts' = Ir) occurs across the internal resistance r of the battery, causing V = E - Ir.

6. 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.

7. Two resistors of resistance R and 2R are connected in PARALLEL across a DC voltage supply. How does the power dissipated in the 2R resistor compare to the R resistor?

  1. It is half as much.
  2. It is twice as much.
  3. It is four times as much.
  4. It is equal.
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Answer: A

In parallel, potential difference V is identical. Power P = V² / R. Therefore, P ∝ 1R. The 2R resistor dissipates half the power of the R resistor.

8. What is the unit of electrical resistivity ρ?

  1. Ω
  2. Ω m
  3. Ω m⁻¹
  4. W m⁻¹
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Answer: B

From R = ρ(lA), ρ = R × Al => Ω × m² / m = Ω m (ohm-meter).

9. 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%.

10. Which change will DOUBLE the resistance of a cylindrical uniform copper wire?

  1. Doubling the radius of the wire
  2. Doubling the cross-sectional area of the wire
  3. Doubling the length of the wire
  4. Halving the length of the wire
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Answer: C

From R = ρ(lA), resistance R is directly proportional to length l. Doubling l doubles the resistance.

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