NCERT Solutions Class 7 Science Chapter 14
Electric Current and its Effects
Q.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.
Ans.
Q.2.Draw the circuit diagram to represent the circuit shown in fig. 14.9.
Q.3.Fig. 14.11 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.
Ans: The cells are connected to each other to make a battery. In, a battery
the negative end of a cell is connected to the positive end of the other cell.
Hence, the cells are connected by opposite ends to make a battery.
Q.4.The bulb in the circuit shown in fig. 14.13 does not glow. Can you identify the problem?
Make necessary changes in the circuit to make the bulb glow.
Ans: The bulb is not glowing because the cell is not Connecting
systematically, the cells of a battery should be connected by opposite
ends. So, the correct connection of the circuit will be:
Q.5. Name any two effects of electric current.
Ans. When an electric current is passed through any device or wire, then it
shows heating and magnetic effect through the wire.
Hence, the two effects of electric current are the heating effect and
magnetic effect.
Q.6.When the current is switched on through a wire, a
compass needle kept nearby gets deflected from its north-
south position. Explain.
When the current is passed through a wire then the wire behaves like a
tiny magnet. This is called the magnetic effect of current. So, when we
keep a compass needle near that current flowing wire, it gets deflected
from its north-south position due to the magnetic field produced by the
wire.
7. Will the compass needle show the deflection when the switch in
the circuit shown by Fig. 14.24 is closed?
Ans: When the switch of the circuit is in a closed position then the circuit is
not complete and no flow of current will take place in this case. No flow of
current means no magnetic field produced. The compass needle shows
deflection only in the presence of a magnetic field. Hence, the compass
needle did not show deflection when the switch was off.
8. Fill in the blanks
a) Longer line in the symbol represents the __________terminal.
Ans: Longer line in the symbol represents the positive terminal.
b) The combination of two or more cells is called _______.
Ans: The combination of two or more cells is called battery.
c) When a current is switched ON in a room heater, it _________.
Ans: When a current is switched ON in a room heater, it produces heat.
d) The safety device based on the heating effect of electric current is
called _______.
Ans: The safety device based on the heating effect of electric current is
called a 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.
Ans: F
b) When the current through the fuse exceeds a certain limit, the
fuse wire melts and breaks.
Ans: T
c) An electromagnet does not attract a piece of iron.
Ans: F
d) An electric bell has an electromagnet.
Ans: T
10. Do you think an electromagnet can be used for
separating plastic bags from a garbage heap? Explain.
Ans: An electromagnet can be made by flowing electricity
through the conductor or wire. It only attracts electromagnetic
materials like iron. It does not attract plastic or plastic bags. So, it
cannot be used to separate plastic bags from the garbage as it is
not attracted by an electromagnet.
11. An electrician is carrying out some repairs in your house. He
wants to replace a fuse with a piece of wire. Would you agree?
Give reasons for your response.
Ans: The fuse is made of a very low melting point wire So when
the amount of electricity exceeds a limited amount of electricity.
Then it melts and breaks, so our home is safe from short
circuits. But the melting point of the metallic wire is high and it
won't melt and break when the amount of electricity exceeds. So,
we did not allow him to replace the fuse with a wire.
12. Zubeida 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 Zubeida in identifying the
possible defects in the circuit.
Ans: There can be several defects in a circuit due to which the
bulb does not glow. Some of the common defects may be;
i) The connection of the wire to the cell and bulb may be
loose.
ii) The cell used in the circuit may be used up.
iii) The switch is defective.
iv) The bulb is fused.
Q.13. In the circuit shown in fig. 14.17.
Would any of the bulb glow when the switch is in the ‘OFF’ position?
What will be the order in which the bulbs A, B and C will glow when the switch is
moved to the ‘ON’ position?
Ans. No bulb will glow.
All bulbs will glow simultaneously.
