The cable of an electric fan becomes so worn that the live wire makes electrical contact with the metal case The case is earthed The plug to the fan contains a 5 A fuse There is a current of 4 A when the fan works normally What will happen in this case?

The current will run to earth and the fuse will not be affected

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The metal case will become very hot

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The metal case will become live and dangerous

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The fuse will melt and switch off the circuit

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Solution

The correct option is D The fuse will melt and switch off the circuit
Answer is D.

When the live wire (high potential) is in contact with the earthed metal case (zero potential) and since there is a potential difference, current flows. As there is little to no resistance in the completed path, the current flow is very large (larger than 4 A melting the fuse). The fuse melts due to high current surge and switches off the circuit.

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Similar questions

Write true or false for each statement:

(a) A fuse wire has a high melting point.

(b) Flow of protons constitutes electric current.

(d) S.I. unit and commercial unit of electrical energy are same.

(e) Overloading of electric current in circuits can lead to short circuiting.

(f) Our body can pass electricity through it.

(g) The metallic cases of all appliances are insulators of electricity.

(h) The earth wire protects us from an electric shock.

(i) A switch should not be touched with wet hands.

(j) All electrical appliances in a household circuit work at the same voltage.

(k) In a cable,the green wire is the live wire.

(l) A fuse is connected to the live wire.

(m) A switch is connected to the neutral wire.

Question 2

Choose the statement which is not correct in the case of an electric fuse.

(a) Fuses are inserted in electric circuits of all buildings

(b) There is a maximum limit on the current which can safely flow through the electric circuits

(d) If a proper fuse is inserted in a circuit it will blow off if current exceeds the safe limit

A power circuit uses a cable having three different wires.

(a) Name the three wires of the cable.

(b) Between which of the two wires should the heating element of an electric geyser be connected?

(d) To which wire should the switch and fuse be connected?

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