Question

Explain in brief the function of an electric fuse in a domestic circuit. An electric heater of current rating 3 kW; 220 V is to be operated in an electric circuit of rating 5 A. What is likely to happen when the heater is switched ‘ON’? Justify your answer with necessary calculation.

Answer 1

Step 1: Function of an Electric Fuse in a Domestic Circuit:
An electric fuse is a safety device used in electrical circuits to protect the circuit from excessive current. It contains a wire that melts when the current exceeds a safe limit, thus interrupting the flow of electricity and preventing damage to electrical appliances or fire hazards.
- The fuse is connected in series with the circuit, and when the current exceeds the rated value, the fuse wire heats up and melts, breaking the circuit and stopping the flow of current.

Step 2: Situation with the Electric Heater:
We are given:
- Power rating of the electric heater = 3 kW = 3000 W
- Voltage = 220 V
- Current rating of the electric circuit = 5 A
To determine what will happen when the heater is switched ON, we need to calculate the current required by the heater using the formula for electrical power:
\[ P = V \times I \] where:
- P is the power (in watts),
- V is the voltage (in volts),
- I is the current (in amperes).
Rearranging the formula to find the current: \[ I = \frac{P}{V} \] Substitute the given values: \[ I = \frac{3000}{220} \approx 13.64 \, \text{A} \] The heater requires a current of approximately 13.64 A to operate, which is much higher than the circuit's current rating of 5 A.

Step 3: What is likely to happen:
Since the current required by the heater (13.64 A) exceeds the current rating of the circuit (5 A), the circuit will not be able to handle this current safely. The following is likely to happen:
- The fuse in the circuit will blow because the current exceeds the fuse’s rated capacity, interrupting the circuit to prevent any damage.
- This is a safety feature to protect the wiring and electrical appliances from overheating and potential damage.

Step 4: Conclusion:
When the heater is switched ON, it will draw a current of approximately 13.64 A, which is greater than the circuit’s 5 A rating. This will cause the fuse to blow, cutting off the power supply and protecting the circuit from damage.