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

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Question 18:

Paheli took a wire of length . Boojho took a wire of of the same material and thickness. Both of them connected the wires as shown in the circuit given in Figure. The current flowing in both the circuits is the same.

  1. Will the heat produced in both the cases be equal? Explain.

  2. Will the heat produced be the same if the wires taken by them are of equal lengths but of different thickness?

As showing in images is a electric Circuit

Electric Circuit

As showing in images is a electric Circuit

Answer:

  1. No, the amount of heat produced in both the cases will not be equal. Amount of heat produced in a wire depends upon the length of the wire.

  2. No, the amount heat produced in the wire depends upon the thickness of the wire.

Question 19:

How does the magnetic effect of electric current help in the working of an electric bell? Explain with the help of a diagram.

Answer:

As depicted in the diagram, when switch is in ON position, electric current passes through the coil or solenoid. By the phenomenon of magnetic effect of current, the coil or solenoid gets magnetized which attracts nearby soft iron armature and the hammer strikes the gong to produce a sound.

Thus, electric bell start ringing and as soon as switch is OFF, no current flows through the coil and its magnetization stops. So, bell stops ringing.

Image of working of electric bell

Working of Electric Bell

Image of working of electric bell

Question 20:

Draw the symbols of the following circuit components.

  1. Electric cell

  2. Switch in off position

  3. Electric bulb

  4. Battery

Answer:

As showing in images is a electric Symbols

Electric Symbols

As showing in images is a electric Symbols