NTS PESCO / HESCO / QESCO / MEPCO Clerk Everyday Science: Electricity MCQs

NTS PESCO / HESCO / QESCO / MEPCO Clerk Everyday Science: Electricity MCQs — sample questions

1. Question 1

   Q1. Which energy conversion takes place in a solar cell?

   • A) Chemical energy to electrical energy
   • B) Mechanical energy to electrical energy
   • C) Light energy to electrical energy
   • D) Thermal energy to electrical energy

   Answer: Light energy to electrical energy

   Explanation: Solar cells (photovoltaic cells) convert light energy (photons) directly into electrical energy through the photovoltaic effect.

2. Question 2

   Q2. What is the unit of electric resistance?

   • A) Ampere
   • B) Volt
   • C) Watt
   • D) Ohm

   Answer: Ohm

   Explanation: Electric resistance is measured in Ohms (Ω), named after physicist Georg Ohm who formulated Ohm's Law: V = IR.

3. Question 3

   Q3. In an electric circuit, voltage (V), current (I), and resistance (R) are related by:

   • A) V = I / R
   • B) V = R / I
   • C) V = I² × R
   • D) V = I × R

   Answer: V = I × R

   Explanation: Ohm's Law states V = IR (Voltage = Current × Resistance); for example, a 2 A current through a 5 Ω resistor produces V = 2 × 5 = 10 V.

4. Question 4

   Q4. An electrician must check whether a household fuse path is broken without calculating resistance from scratch on paper. Which meter is most directly used to test continuity or resistance in a circuit?

   • A) An ammeter is inserted in series to measure current
   • B) A voltmeter is placed across components to measure voltage
   • C) An ohmmeter measures electrical resistance of a path
   • D) A wattmeter measures electric power drawn by a load

   Answer: An ohmmeter measures electrical resistance of a path

   Explanation: An ohmmeter applies a small known voltage across a circuit path and measures the resulting current, then displays the calculated resistance; it is the standard tool for testing whether a fuse, wire, or component is intact or open-circuit.

5. Question 5

   Q5. A school debate pits early bulb rivals but one name dominates mass classroom stories about filaments and central-station lighting rollouts. Edison is most commonly highlighted for helping make which lighting pathway practical for homes and streets?

   • A) Carbon-filament incandescent lamp systems scaled for everyday use
   • B) Room-scale cold-cathode fluorescent tubes before vacuum pumps
   • C) Consumer LED bulbs with blue-gallium chips in 1879 household kits
   • D) Domestic CO2 laser lighting kits sold before carbon filaments

   Answer: Carbon-filament incandescent lamp systems scaled for everyday use

   Explanation: Thomas Edison developed a practical carbon-filament incandescent lamp in 1879 and, crucially, built the infrastructure - generators, distribution wiring, and metering - needed to deliver electricity to homes and streets at commercial scale. Earlier experimenters had created arc lights or short-lived filament lamps, but Edison's system made electric lighting a consumer product.

6. Question 6

   Q6. Ohm's Law is represented by which formula?

   • A) V = I/R
   • B) V = IR
   • C) V = I²R
   • D) V = R/I

   Answer: V = IR

   Explanation: Ohm's Law states that voltage equals current multiplied by resistance (V = IR), where V is in volts, I in amperes, and R in ohms; it applies to ohmic (linear) conductors where resistance remains constant.

7. Question 7

   Q7. What is the standard household AC supply voltage in Pakistan?

   • A) 110 V
   • B) 220 V
   • C) 240 V
   • D) 380 V

   Answer: 220 V

   Explanation: Pakistan's national electricity grid supplies alternating current at 220 V (nominal) and 50 Hz; this is the standard declared by NEPRA and matches the supply voltage used throughout most of South Asia and Europe.

8. Question 8

   Q8. Electric power dissipated in a resistor can be calculated using which formula?

   • A) P = V/I
   • B) P = I²R
   • C) P = IR²
   • D) P = V²/I

   Answer: P = I²R

   Explanation: Electric power dissipated in a resistor can be written as P = I²R (derived from P = IV and V = IR); this shows power increases with the square of current, which is why resistance heating is used in appliances.

9. Question 9

   Q9. A step-up transformer has 100 turns in the primary coil and 1,000 turns in the secondary coil. If the primary voltage is 50 V, what is the secondary voltage?

   • A) 5 V
   • B) 50 V
   • C) 100 V
   • D) 500 V

   Answer: 500 V

   Explanation: For a transformer, the voltage ratio equals the turns ratio: Vs/Vp = Ns/Np, so Vs = 50 × (1000/100) = 500 V. Because this output voltage exceeds the input, it is a step-up transformer.

10. Question 10

    Q10. Which statement correctly distinguishes AC from DC electric current?

    • A) AC periodically reverses direction while DC flows in one constant direction
    • B) AC flows in one direction while DC reverses direction periodically
    • C) AC is used in batteries while DC is used in power grids
    • D) AC has higher voltage than DC in all applications

    Answer: AC periodically reverses direction while DC flows in one constant direction

    Explanation: Alternating current (AC) reverses polarity at a fixed frequency (50 or 60 Hz in power grids); direct current (DC) flows in one constant direction, as produced by batteries. AC is used in power grids because it is easily transformed to different voltages.

11. Question 11

    Q11. A transformer that increases the output voltage above the input voltage is called a:

    • A) Step-down transformer
    • B) Isolation transformer
    • C) Current transformer
    • D) Step-up transformer

    Answer: Step-up transformer

    Explanation: A step-up transformer has more turns in the secondary coil than the primary, so the output (secondary) voltage is higher than the input (primary) voltage. Step-down transformers do the reverse, reducing voltage, and both types rely on electromagnetic induction.

12. Question 12

    Q12. What is the frequency of the AC electrical supply in Pakistan?

    • A) 25 Hz
    • B) 40 Hz
    • C) 60 Hz
    • D) 50 Hz

    Answer: 50 Hz

    Explanation: Pakistan's national electrical grid operates at 50 Hz AC, the same standard as Europe and most of Asia, meaning the current direction reverses 50 times per second (100 half-cycles).

13. Question 13

    Q13. What is the SI unit of electrical resistance?

    • A) Volt
    • B) Ampere
    • C) Ohm
    • D) Farad

    Answer: Ohm

    Explanation: The ohm (Ω) is the SI unit of electrical resistance, defined as the resistance between two points when a potential difference of one volt drives a current of one ampere. It is named after physicist Georg Simon Ohm, who formulated Ohm's Law.

14. Question 14

    Q14. Ohm's Law states that the current through a conductor is:

    • A) directly proportional to voltage
    • B) inversely proportional to voltage
    • C) directly proportional to resistance
    • D) independent of resistance

    Answer: directly proportional to voltage

    Explanation: Ohm's Law states that the current (I) through a conductor between two points is directly proportional to the voltage (V) across those points, expressed as I = V/R, where R is the constant resistance. This means that doubling the voltage doubles the current, provided temperature and resistance remain constant.

15. Question 15

    Q15. The mathematical form of Ohm's Law is:

    • A) V = IR
    • B) V = IR²
    • C) V = I/R
    • D) V = I + R

    Answer: V = IR

    Explanation: Ohm's Law states that the voltage across a conductor equals the current flowing through it multiplied by its resistance: V = IR. This linear relationship holds for ohmic conductors at constant temperature and is fundamental to the analysis of all electrical circuits.

16. Question 16

    Q16. Electrical power in a circuit is given by:

    • A) P = VI
    • B) P = V²/I
    • C) P = V/I
    • D) P = V + I

    Answer: P = VI

    Explanation: Electrical power is the rate of energy transfer; P = VI where V is potential difference in volts and I is current in amperes, giving power in watts. This can also be expressed as P = I²R or P = V²/R using Ohm's Law.

17. Question 17

    Q17. Joule's law of heating states that heat produced is proportional to:

    • A) I²Rt
    • B) resistance only
    • C) current only
    • D) voltage only

    Answer: I²Rt

    Explanation: Joule's law of heating states that the heat Q produced in a conductor is proportional to the square of the current (I²), the resistance (R), and the time (t), expressed as Q = I²Rt. This relationship shows that doubling the current quadruples the heat generated, which is why high-resistance, high-current circuits generate significant waste heat.

18. Question 18

    Q18. In a series circuit, the total resistance is:

    • A) the sum of all individual resistances
    • B) equal to the largest resistance
    • C) less than the smallest resistance
    • D) the product of all resistances

    Answer: the sum of all individual resistances

    Explanation: In a series circuit, current flows through each resistor sequentially, so the same current experiences each resistance in turn; the total opposition equals the arithmetic sum of all individual resistances: R_total = R₁ + R₂ + … + Rₙ.

19. Question 19

    Q19. In a parallel circuit, the total resistance is:

    • A) less than the smallest individual resistance
    • B) the sum of all resistances
    • C) greater than any individual resistance
    • D) equal to the average resistance

    Answer: less than the smallest individual resistance

    Explanation: In a parallel circuit, reciprocal resistances add: 1/R_total = 1/R₁ + 1/R₂ + …; the total resistance is always less than the smallest individual resistance, allowing more current to flow than through any single branch.

20. Question 20

    Q20. When resistors are connected in parallel, which quantity remains the same across all resistors?

    • A) Current
    • B) Resistance
    • C) Power
    • D) Voltage

    Answer: Voltage

    Explanation: In a parallel circuit, all branches are connected directly across the same two nodes, so each component experiences the same potential difference (voltage); current divides among branches according to their individual resistances.