Chapter 14 Electric Current and Its Effects

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Exercise 1 ( Page No. : 172 )

•  Q1 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: Following are the symbles of the components of electric circuit are as follows: Q2 Draw the circuit diagram to represent the circuit shown in Fig.14.21. Ans: In the given circuit one terminal of the bulb is connected to the safety pin and another end is connected to the cell. Here, the circuit is not complete because the safety pin is not connected to the cell. Hence, safety pin shows off position of the switch. Q3 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. Ans: In order to make battery, the positive terminal (+) of one cell should be connected to the (-) terminal of another cell and so on. Battery or we can say cell should be connected in series. Q4 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. Ans: In this circuit, the bulb is not glowing because the cells are not connected properly. The cells should be connected like positive terminal of the one cell is connected to the negative terminal of another cell. To make the bulb glow cells should be connected properly. Q5 Name any two effects of electric current. Ans: The two main effects of electric current are as follows: 1. Heating effect of electric current: It may be defined as the electric current passes through the wire, it gets hot; it is known as the heating effect of the electric current. For example: heater, geezer, hair dryer etc. 2. Magnetic effect of electric current: It is also called as electromagnetic effect. When electric current is passed through a conducting wire then the magnetic field generate around it. It is called as the magnetic effect of the electric current. For example: Electric bell, electric motor, electric fan etc. Q6 When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain. Ans: When the electric current is passed through a wire, it starts to behave like a magnet. So, when a compass needle is kept near a current carrying wire, it affects by the magnetic effect of electric current and show deflection from its north- south position. Q7 Will the compass needle show deflection when the switch in the circuit shown by Fig.14.24 is closed? Ans: No, the compass needle will not show any deflection when the switch is closed because the circuit does not have any source of current. The wire does not behave like a magnet in the absence of current. Q8 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) Positive                                                                                                                                                                                                                                      A cell have two terminals, one is positive and other is negative. The direction of current is from positive terminal to negative terminal. (b) Battery Battery is the combination of two or more cells in which positive terminal of the cell connected to the negative terminal of the another cell. (c) Produces heat It produces heat due to the heating effect of electric current. (d) Fuse Fuse limits the current in circuit and breaks the circuit, if current reaches its maximum limit. Q9 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) False This statement is false because to make a battery the positive terminal of the cell should be connected to the negative terminal of the another cell. (b) True                                                                                                                                                                                                                                               This statement is true because fuse is a safety device which is made up of a special material which have very low melting point. When current passes through a fuse in maximum amount then it melts quickly and break the circuit.  (c) False This statement is false because an electromagnet behaves like a magnet when we passes current through it. So it is obvious that it attracts iron pieces towards it. (d) True This statement is true because electric bell has a piece of iron which is bound by a coil. When we pass the current through the coil, it behaves like an electromagnet. Q10 Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain. Ans: No, the electromagnetic cannot be used for separating plastic bags from garbage heap because the electromagnets only attracts magnetic materials towards itself. Plastic bag is not a magnetic material, so electromagnet will not attract them. Q11 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. Ans: No, the electrician will not be allowed to replace the fuse by piece of wire in the house. This is because a fuse filament cannot be made by any kind of wire. It must have a low melting point, so that it could melt easily and break, if the large amount of current is passes through it. Q12 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. Ans: The bulb is not glowing because of the two reasons. These are as follows: One reason could be that may be the two cells are not connected properly. For the bulb to glow, the negative terminal of the one cell must be connected to the positive terminal of the another cell. The another reason may be that the cell holder may not be tightly bound by the rubber band to keep the two cells in contact with each other. The circuit will not be complete and current will not flow through the circuit if the cells are not in contact with each other properly. Q13 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? Ans: (i) No, the bulb will not glow when the switch is in the off position because the current will not pass through the circuit in the switch 'OFF' position. (ii) When the switch is moved to the 'ON' postion, all bulbs will glow simultaneously because all the bulbs are connected to the same switch and same belt.