Class 7 Science NCERT Solutions for Chapter – 14 Electric Current and its Effects

Electric Current and its Effects

Question 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.

Solution:
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 1

Question 2.
Draw the circuit diagram to represent the circuit shown
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 2
Solution:
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 3

Question 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.
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 4
Solution:

NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 5

Question 4.
The bulb in the circuit shown does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 6
Solution:
The problem with the circuit is that both the negative terminals are connected to the bulb.
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 7

Question 5.
Name any two effects of electric current.

Solution:

  1. Heating effect
  2. Magnetic effect.

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

Solution:
When electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current due to attraction of the wire. So, the compass needle which is a magnet, gets deflected.

Question 7.
Will the compass needle show deflection when the switch in the circuit shown by is closed?
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 8
Solution:
No. Since, there is no cell so, no current will flow.

Question 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 affect of electric current is called a ………. .

Solution:
(a) positive
(b) battery
(c) get heated
(d) fuse.

Question 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)

Solution:
(a) F
(b) T
(c) F
(d) T.

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

Solution:
No. This is because electromagnets can only attracts magnetic materials. Plastic bag is a non-magnetic material and will not be attracted by an electromagnet.

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.

Solution:
No, we would not agree to replace the fuse by a wire. The electric wire will not melt even if high current flows through it. So, it will not prevent the damage done by high current.

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

Solution:
One of the reasons may be that the rubber band used in the cell holder may not be tight enough to keep the two cells in contact with each other. If the cells are not in proper contact with each other, then the circuit will not be complete and current will not flow through the circuit. Hence, the bulb will not glow.

The other reason may be that the two cells are not connected properly. The negative.terminal of one cell must be connected to the positive terminal of the other cell.

Question 13.
In the circuit shown
NCERT Solutions for Class 7 Science Chapter 14 Electric Current and its Effects image 9

  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?

Solution:

  1. No bulb will glow
  2. All bulbs will glow at a time.

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