NCERT Solutions for Class 7th Science
Chapter 14 – ELECTRIC CURRENT AND ITS EFFECTS
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
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
Q.2 Draw the circuit diagram to represent the circuit shown in Fig.14.21.
Q.3 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.
Q.4 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.
Q.5 Name any two effects of electric current.
Ans Effects of electric current:
1) Heating effect of electric current: The wire gets hot when an electric current passes through it. This is the heating effect of the electric current. This principle is used in appliances like heater, geyser etc.
2) Magnetic effect of electric current: When electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current. This principle is used in electric bell etc.
Q.6 When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Q.7 Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?
Q.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 ________.
Ans (a) Longer line in the symbol for a cell represents its _positive_ terminal.
(b) The combination of two or more cells is called a _battery_.
Q.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)
Ans (a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (F)
Correct: To make a battery of two cells, the negative terminal of one should be connected to the positive terminal of other.
Q.10 Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Q.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.
Q.12 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.
Q.13 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?