NCERT Solutions for Class 7 Science Chapter 14 Electric Current and Its Effects
NCERT solutions for class 7 science chapter 14 electric current and its effects exercise:
- 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
Answer:
Symbols for various components of electrical circuits are-
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Electric Components |
Symbols |
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Connecting Wires |
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Switch OFF position |
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Bulb |
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Cell |
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Switch ON position |
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Battery |
- Draw the circuit diagram to represent the circuit shown in Fig.14.21.
Answer:
In the above figure, one end of the cell is connected to bulb and the other is connected to switch. The switch is in OFF position. One end of the bulb is connected to switch and the other is with the cell.
The circuit diagram of the above-given figure is-
- 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.
Answer:
To make a battery from the four cell we need to connect the one positive end of a cell to the negative end of the other cell. In this way, we can form a four-cell battery.
- 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.
Answer:
The problem in the above circuit diagram is that cells are not connected properly, both the positive terminal of a cell is connected. To glow bulb, the positive end of the cell must be connected with the negative end of the other cell. As shown in the figure:-
- Name any two effects of electric current.
Answer:
The two effects of electric current are-
(i) Heating effect- When current is passing through the wires, the wires become hot and produces heat.
(ii) Magnetic Effect - When current is passing through the wires, it behaves like a magnet.
- When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Answer:
When the current is passing through the wires, it behaves like a magnet and rises to a magnetic field around it which exerts a magnetic force on the compass needle and reflects it from North-South position.
- Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?
Answer:
No, Because in the above circuit diagram there is no source of current supply like battery or cell. In the absence of current wire will not act as a magnet, and hence needle will not show any deflection.
- 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) Produces heat (due to the heating effect of current)
(d) Fuse (When a large amount of current is flowing through the wire, it melts and break the circuit)
- 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, Negative terminal should be connected to the positive terminal of the other cell
(b) True, The wire of fuse is of low melting point. So, when the heat due to current is higher than a certain limit, it melts quickly and breaks the circuit
(c) False, A magnet always attracts the iron piece.
(d) True,
- Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Answer:
No, because the plastic bag is non-magnetic in nature and hence it is not attracted by the electromagnets from the garbage heap.
- 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, I m not agree with the electrician because the fuse wire should have a low melting point. So, that it can quickly melt and break the circuit.
The ordinary wire has a high melting point as compare to fuse wire. Thus it cannot be used in fuse wires.
- 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.
Answer:
The following defects may be presents in the circuits-
- The rubber band used in the cell holder may not be tight enough to keep the cells in proper contact.
- The two cells may not be properly connected. We must connect the negative terminal to the positive end of the other cell.
- The bulb may be fused.
- Circuit connection may be loose. etc
- 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?
Answer:
(i) No, because the circuit connection does not compete for any bulb so, that flow of current is not possible.
(ii) Bulbs will glow simultaneously
All the bulbs will glow at once.