Study Materials

NCERT Solutions for Class 7th Science

 

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Chapter 14. Electric Current and its Effects

NCERT Exercise

 

 

 

Exercise 


1. 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

2. Draw the circuit diagram to represent the circuit shown in.

3. 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.  

4. The bulb in the circuit shown in does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow. 

5. Name any two effects of electric current.

Answer:

(i) Heating effect, (ii) Magnetic effect.

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

Answer:

When electric current passes through a wire, it behaves like a magnet. this is the ellectric current. So, the compass needle which is a magnet, gets deflected.

7. Will the compass needle show deflection when the switch in the circuit shown by  is closed?  

8. 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___________ .

Answer:

(a) positive, (b) battery, (c) gets effected, (d) fuse.

9. 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 electromagnet. (T/F)

Answer:

(a) false, (b) true, (c) false, (d) true.

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

Answer:

No. Electromagnet do not attract plastic.

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:

No. The wire may not melt even if high current flows through it. So, it will not prevent the damage done by high current. 

12. Zubeda made an electric circuit using a cell holder shown in , 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:

(i) Bulb taken would be fuse.

(ii) Cell taken could be exhausted.

(iii) In cell holder, she would have connected the same terminal of the cells.  

13. In the circuit shown in

(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?

Answer:

(i) No.

(ii) All bulb will glow at the same time.

 

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