NCERT Class VII Science Solutions: Chapter 14-Electric Current and its Effects Part 4

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Question 11:

An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.

Answer:

Fuse is a device that is a safeguard to all of our electrical appliances. They are made up of special material which melt quickly and break when a large electric currents passed through it.

If the electrician does not use proper fuse wire, instead he uses any ordinary electric wire as fuse, it increases the risk of overheating of wires due to flow of excessive current. It may lead to short circuit in electric equipment and these appliances may catch fire. It is advised to use standard fuse wire or MCBs to prevent electrical accidents.

This diagram shows the heating effect of the electric curren …

The Heating Effect of the Electric Current

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Question 12:

Zubeda made an electric circuit using a cell holder, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit.

Answer:

Possible reasons are as follows:

  • The bulb may be fused or defective.

  • Cells are not connected properly.

  • There may be loose connections.

  • The switch is not functioning well.

  • The cells are dried up i.e. the power of the cell has been exhausted.

Question 13:

In the circuit shown in Fig.

As showing in images is a Electrical circuit

Electrical Circuit

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  1. Would any of the bulb glow when the switch is in the ‘OFF’ position?

  2. What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?

Answer:

  1. None of the bulb will glow when the witch is in the OFF position, since the electric circuit is not closed.

  2. When the switch is moved to 'ON' position, circuit is complete and electric current will flow immediately. All of the bulbs will glow instantly