(a) A student wants to use an electric heater, an electric bulb and an electric fan simultaneously. How should these gadgets be connected with the mains? Justify your answer giving three reasons.

(b) What is an electric fuse? How is it connected in a circuit?

Electricity

Practical Applications of Heating Effect and Domestic Circuits

Official Answer

(a) The gadgets (electric heater, electric bulb, and electric fan) should be connected in parallel with the mains.

Justification (Three Reasons):

Independent Operation: In a parallel circuit, each appliance has its own independent switch. If one appliance is switched off or fails, the other appliances continue to function normally.
Constant Voltage: Each appliance receives the full mains voltage (typically $220\text{ V}$ ), which is necessary for them to operate at their rated power.
Appropriate Current Distribution: Different appliances have different resistances and require different currents to operate. In a parallel connection, the current divides among the appliances according to their requirements ( $I = V/R$ ), whereas in series, the same current would flow through all, preventing them from working efficiently.

(b) Electric Fuse: An electric fuse is a safety device consisting of a wire made of a material with a low melting point and high resistivity (such as an alloy of lead and tin). It protects electrical circuits and appliances from damage due to excessive current (overloading or short-circuiting) by melting and breaking the circuit.

Connection: It is always connected in series with the live wire before the current enters the domestic appliances.

parallelindependent switchconstant voltagecurrent dividessafety devicelow melting pointserieslive wire

Marking Scheme

1Identification of parallel connection: 0.5 mark
2Three valid reasons for parallel connection: 1.5 marks (0.5 mark each)
3Definition of electric fuse: 0.5 mark
4Correct connection of fuse (in series with live wire): 0.5 mark

Hint

Think about how turning off a light bulb in your room does not turn off the fan, and recall which wire carries the high potential into the house.

Quick Oral Answer

An electric fuse is a safety device with a low melting point wire connected in series with the live wire. It melts and breaks the circuit when current exceeds a safe limit, protecting appliances from damage.

Analysis & Explanation

In domestic wiring, parallel connection is preferred over series connection because it ensures that the failure of one appliance does not disrupt the entire circuit. Additionally, appliances designed for domestic use require a constant voltage of $220\text{ V}$ to operate at their rated power, which is only possible in a parallel configuration. An electric fuse acts as a sacrificial safety barrier; when current exceeds the safe limit, Joule heating ( $H = I^2 R t$ ) raises the temperature of the fuse wire to its melting point, causing it to melt and safely isolate the household circuit from the mains supply.

Common Mistakes

1Suggesting that domestic appliances should be connected in series.
2Stating that a fuse is connected in parallel (which would cause a catastrophic short circuit).
3Connecting the fuse to the neutral wire instead of the live wire.

Interesting Facts

The standard domestic voltage in India is $220\text{ V}$ AC at a frequency of $50\text{ Hz}$ .

Fuses are being rapidly replaced by MCBs (Miniature Circuit Breakers) in modern household wiring because MCBs can be reset easily without needing wire replacement.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2022?

This question carries 3 marks in the CBSE Class 10 Science 2022 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Electricity" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Practical Applications of Heating Effect and Domestic Circuits" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2022 paper?

This is a Short Answer question from Section B in the CBSE Class 10 Science 2022 paper.