Solution of Chapter 14. Electric Current and Its Effects (NCERT Science Book)

Draw in your notebook the symbols to represent the following components of electrical circuits: connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ‘ON’ position, and battery

Draw the circuit diagram to represent the circuit shown in Fig.14.21.

Fig.14.22 shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four

cells.

The bulb in the circuit shown in Fig.14.23 does not glow. Can you

identify the problem? Make necessary changes in the circuit to make

the bulb glow.

Name any two effects of electric current.

When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.

Will the compass needle show deflection when the switch in the circuit shown in Fig. 14.69 is closed?

Fill in the blanks:

a. Longer line in the symbol for a cell represents its ________terminal.

b. The combination of two or more cells is called a ______.

c. When current is switched ‘on’ in a room heater, it ___________.

d. The safety device based on the heating effect of electric current is called a _________.

Mark “T” if the statement is true and “F” if it is false:

a. To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)

b. When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)

c. An electromagnet does not attract a piece of iron. (T/F)

d. An electric bell has an electro-magnet. (T/F)

Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.

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.

Zubeda made an electric circuit using a cell holder shown in Fig. 14.4, 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.

In the circuit shown in Fig. 14.25

(i) Would any of the bulb glow when the switch is in the ‘OFF’ position?

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

Set up the circuit shown in Fig. 14.17 again. Move the key to ‘ON’ position and watch careful in which direction the compass needle gets deflected. Switch ‘OFF’ the current. Now keeping rest of the circuit intact, reverse the connections at the terminal of the cell. Again, switch ‘on’ the current. Note the direction in which the needle gets deflected. Think of an explanation.

Make four electromagnets with 20, 40, 60 and 80 turns. Connect them one by one to a battery of 2 cells. Bring the electromagnet near a box of pins. Count the number of pins attracted by it. Compare the strengths of the electromagnets.

Paheli and Boojho saw a magic trick sometime back. The magician placed an iron box on a stand. He then called Boojho and asked him to lift the box. Boojho could easily lift the box. Now the magician made a show of moving his stick around the box while muttering something. He again asked Boojho to lift the box. This time Boojho could not even move it. The magician again muttered something and not Boojho could lift the box.

The audience, including Paheli and Boojho, were very impressed with the show and felt that the magician had some supernatural powers. However, after reading this chapter Paheli wondering if the trick was indeed some magic or some science was involved? Can you guess what science might be involved?

Using an electromagnet, you can make a working model of a railway

signal as shown in Fig.14.26.

Visit an electric shop. Request a mechanic to show you the various

types of fuses and MCB and to explain how they work.