Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Plastic bags are not magnetic substances and thus, electromagnets cannot be used for separating them from garbage heap.
Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed?
Yes, compass needle will show deflection when switch is closed in the given circuit.
Name any two effects of electric current.
The two effects of electric current are as follows:
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.
The correct connection of the terminals of four cells with wires to make a battery is as follows, in which positive side of one battery to the negative side of the other:
Draw the circuit diagram to represent the circuit shown in Fig.14.21.
The electrical components and their relation with each other shown above can be represented by following circuit diagram:
In the circuit shown in Fig. 14.25
(i) Would any of the bulbs 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?
(i) None of the bulbs will glow when switch is in the ‘OFF’ position because circuit remains incomplete and thus, no current will flow in it.
(ii) All the bulbs will glow at once when switch is moved to the ‘ON’ position.
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.
The possible defects which may be found in Zubeda’s circuit are as follows:
1. The terminals of cells are not connected to each other in the correct manner.
2. The connections of wires are loose.
3. The bulb used may have fuse.
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.
No, electric fuse should not be replaced by a piece of wire. It is so because electric fuse protects the circuit against the flow of large amount of electric current which may cause short circuit and eventually fire in the house. Wire in the electric fuse is made up of some special material such that immediately melts down, if large amount of electric current passes through it and breaks down the circuit. Thus, electric fuse prevents short circuit and fires caused by electric current.
When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
The deflection of compass needle in north-south position indicates that as soon as current is switched on through a wire, a magnetic field develops around it. Due to this magnetic field, the wire acts like a magnet which has north and south poles. Formation of magnetic north and south poles deflects the compass needle in north-south position.
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.
The bulb in the given diagram does not glow because positive sides of the cells are shown connected to each other. Rearrange the cells in a manner that negative side of one cell comes in contact with positive side of the other. By reversing the sides of cell, the circuit will complete and bulb will glow.
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)
Fill in the blanks:
(1) Longer line in the symbol for a cell represents its_________ terminal.
(2) The combination of two or more cells is called a___________.
(3) When current is switched ‘on’ in a room heater, it__________.
(4) The safety device based on the heating effect of electric current is called a_______.
(1) Longer line in the symbol for a cell represents its positive terminal.
(2) The combination of two or more cells is called a battery.
(3) When current is switched ‘on’ in a room heater, it produces heat.
(4) The safety device based on the heating effect of electric current is called a electric fuse.
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