Worksheet Solutions: Household Circuits | Physics Class 10 ICSE PDF Download

Part A — Multiple Choice Questions

Q1. The commercial unit of electrical energy used in electricity bills is:

(a) Joule

(b) Erg

(c) Kilowatt hour

(d) Watt

Answer: (c) Kilowatt hour
Explanation: The energy used in homes is measured in kilowatt hour, where 1 kWh = 3.6 × 10⁶ J.

Q2. Which device is safer and faster in protecting a circuit from damage?

(a) Switch

(b) Fuse

(c) Miniature Circuit Breaker (MCB)

(d) Socket

Answer: (c) Miniature Circuit Breaker (MCB)
Explanation: An MCB trips very quickly (in about 25 milliseconds) and can be reset, unlike a fuse.

Q3. Which of the following systems of house wiring allows easy installation of new appliances without extra wires from the distribution board?

(a) Tree system

(b) Series system

(c) Ring system

(d) Parallel system

Answer: (c) Ring system
Explanation: In the ring system, appliances can be added directly to the circuit, making it cheaper and easier.

Q4. The resistance of a filament of a bulb rated 220 V and 100 W is:

(a) 220 Ω

(b) 484 Ω

(c) 100 Ω

(d) 2.2 Ω

Answer: (b) 484 Ω
Explanation: Resistance = V² / P = (220 × 220) ÷ 100 = 484 Ω.

Q5. Which wire is connected to the outer metallic case of an appliance for safety?

(a) Live wire

(b) Neutral wire

(c) Earth wire

(d) Fuse wire

Answer: (c) Earth wire
Explanation: The earth wire directs leakage current safely into the ground, preventing shocks.

Part B — Short Answer Questions

Q6. Define electrical power. Write its unit.
Answer: Electrical power is the rate at which electrical energy is consumed or supplied by a device. It is given by:
P = VI, where V is potential difference and I is current.
The SI unit of power is watt (W).

Q7. Why is the fuse always connected in the live wire of a circuit?
Answer: The fuse is connected in the live wire so that when excessive current flows, it melts and disconnects the appliance from the high potential supply. If it were in the neutral wire, the appliance would still remain connected to the live wire and could cause shock hazards.

Q8. Write any two advantages of connecting household appliances in parallel.
Answer:

1. Each appliance gets the full supply voltage for proper functioning.

2. Appliances work independently; switching off one does not affect others.

Q9. State two differences between the tree system and the ring system of house wiring.
Answer:

• Tree system: Each new appliance may require extra wiring to the distribution board. It is expensive and less flexible.

• Ring system: Appliances can be connected directly to the ring; cost of wiring is lower and faults affect only the specific appliance.

Q10. Why is earthing important in electrical circuits?
Answer: Earthing provides a safe path for leakage current. If the live wire touches the metal case of an appliance, current passes to the ground through the earth wire, blowing the fuse and protecting the user from electric shock.

Part C — Long Answer Questions

Q11. An electric heater of power 2000 W runs for 3 hours daily. Find the total energy consumed in 10 days in kilowatt hours.
Solution:

• Power = 2000 W = 2 kW

• Time per day = 3 hours

• Energy per day = Power × Time = 2 × 3 = 6 kWh

• In 10 days, Energy = 6 × 10 = 60 kWh
  Answer: The heater consumes 60 units of electricity in 10 days.

Q12.  Three appliances of power 500 W, 1000 W and 1500 W are used on a 220 V supply. Calculate the total current and the rating of the fuse needed.
Solution:

• Total power = 500 + 1000 + 1500 = 3000 W

• Voltage = 220 V

• Current = Power ÷ Voltage = 3000 ÷ 220 ≈ 13.6 A

• Fuse rating should be slightly above this current, say 15 A.
  Answer: A 15 A fuse should be used.

Q13. Explain the working of a three-pin plug with the role of live, neutral and earth connections. Why is the earth pin made longer and thicker?
Solution:

• In a three-pin plug:

  • Live pin (L): Supplies current from the mains.

  • Neutral pin (N): Provides return path for current.

  • Earth pin (E): Connects to the metallic case of appliance for safety.

• The earth pin is longer so that it connects first, ensuring safety before current flows.

• It is thicker so that it cannot be mistakenly inserted into live or neutral slots.
  Answer: The three-pin plug ensures safe supply by providing proper live, neutral, and earth connections. The long and thick earth pin guarantees user protection.