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1. What does an electric circuit mean?, , Answer, , A continuous and closed path of an electric current is called an electric circuit. An electric circuit, consists of electric devices, source of electricity and wires that are connected with the help of a, switch., , 2. Define the unit of current., , Answer, , The unit of electric current is ampere (A). 1 Ais defined as the flow of 1 C of charge througha, wire in1s., , 3. Calculate the number of electrons constituting one coulomb of charge., , Answer, , One electron possesses a charge of 1.6 x10°7°C, i-e., 1.6 x10°7°C of charge is contained in 1, electron., , -. 1 C of charge is contained in 1/1.6 x 107° = 6.25 x 107* = 6 x 107*, , Therefore, 6 x 1018 electrons constitute one coulomb of charge., , Page No: 202, , 1. Name a device that helps to maintain a potential difference across a conductor., , Answer, , Any source of electricity like battery, cell, power supply, etc. helps to maintain a potential, difference across a conductor., , 2. What is meant by saying that the potential difference between two points is 1 V?, , Answer, , If 1 J of work is required to move a charge of amount 1 C from one point to another, then it is, said that the potential difference between the two points is 1 V., , 3. How much energy is given to each coulomb of charge passing through a 6 V battery?, Answer, , The energy given to each coulomb of charge is equal to the amount of work which is done in, moving it., , Now we know that,, , Potential difference = Work Done/Charge, , -“. Work done = Potential difference x charge, , Where, Charge = 1 C and Potential difference = 6 V, , -. Work done = 6x1, , = 6 Joule., , Page No: 209, , 1. On what factors does the resistance of a conductor depend?, , Answer, , The resistance of a conductor depends upon the following factors:, , > Length of the conductor, , +> Cross-sectional area of the conductor, , +> Material of the conductor, > Temperature of the conductor

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2. Will current flow more easily through a thick wire or a thin wire of the same material, when, connected to the same source? Why?, , Answer, , The current will flow more easily through thick wire. It is because the resistance of a, conductor is inversely proportional to its area of cross - section. If thicker the wire, less is, resistance and hence more easily the current flows., , 3. Let the resistance of an electrical component remains constant while the potential difference, across the two ends of the component decreases to half of its former value. What change will, occur in the current through it?, , Answer, , According to Ohm’s law, V=IR, , => I=V/R... (1), , Now Potential difference is decreased to half, , -. New potential difference V’=V/2, , Resistance remains constant, , So the new current I’= V’/R, , = (V/2)/R, , = (1/2) (V/R), , = (1/2) 1=1/2, , Therefore, the amount of current flowing through the electrical component is reduced by half., , 4. Why are coils of electric toasters and electric irons made of an alloy rather than a pure, metal?, , Answer, The resistivity of an alloy is higher than the pure metal. Moreover, at high temperatures, the, , alloys do not melt readily. Hence, the coils of heating appliances such as electric toasters and, electric irons are made of an alloy rather than a pure metal.

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5. Use the data in Table 12.2 to answer the following Table 12.2 Electrical resistivity of some substances at 20°C, , , , , , , , , , , , , , , , , , , , , , , , - Material Resistivity (Q m), , Conductors | Silver 1.60 x 10°*, Copper 1.62=x10°°, Aluminium 2.63 x 10°*, Tungsten 5.20 x 10-8, Nickel 6.84 x 10°*, Iron 10.0 x 10°*, Chromium 129x310", Mercury 94.0 x 10°*, Manganese 1.84 x 10°©, Constantan 49=x10¢, (alloy of Cu and Ni), , , , , , , , , , , , , , , , , , , , , , , , , , Alloys Manganin 44~=x10°, (alloy of Cu, Mn and Ni), Nichrome 100 x 10°*, (alloy of Ni, Cr, Mn and Fe), Glass 101° — 1074, Insulators Hard rubber 1077 — 16%*, Ebonite 1075 — 107”, Diamond 107? — 1073, Paper (dry) 40", , , , , , , , , , , , Answer, , (a) Resistivity of iron = 10.0x 108 Q, , Resistivity of mercury = 94.0 x 10°?Q, , Resistivity of mercury is more than that of iron. This implies that iron is a better conductor than, mercury., , , , (b) It can be observed from Table 12.2 that the resistivity of silver is the lowest among the listed, materials. Hence, it is the best conductor., , Page No: 213, , 1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 Veach,aS, Q resistor, an 8 Q resistor, and a 12 Q resistor, and a plug key, all connected in series., , Answer, , Three cells of potential 2 V, each connected in series therefore the potential difference of the, battery will be 2 V+ 2 V+ 2 V= 6V. The following circuit diagram shows three resistors of, resistances 5 Q, 8 Q and 12 Q respectively connected in series and a battery of potential 6 Vand, a plug key which is closed means the current is flowing in the circuit.

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Page No: 213, , 1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 Veach,a5S, Q resistor, an 8 Q resistor, and a 12 Q resistor, and a plug key, all connected in series., , Answer, , Three cells of potential 2 V, each connected in series therefore the potential difference of the, battery will be 2 V+ 2 V+ 2 V=6vV. The following circuit diagram shows three resistors of, resistances 5 QO, 8 Q and 12 QO respectively connected in series and a battery of potential 6 Vand, a plug key which is closed means the current is flowing in the circuit., , , , sa sa zmoQ, ASN ANSI, vy, ->, = Vo?, , , , , , , , 2. Redraw the circuit of question 1, putting in an ammeter to measure the current through the, resistors and a voltmeter to measure potential difference across the 12 Q resistor. What would, be the readings in the ammeter and the voltmeter?, , Answer, An ammeter should be connected in the circuit in series with the resistors. To measure the, , potential difference across the resistor it should be connected in parallel, as shown in the, following figure., , , , , , , , , , , , , , , , s$2 sQ, = Wr, Lge, fa} =A)., <=2 p, , The resistances are connected in series., , Ohm’s law can be used to obtain the readings of ammeter and voltmeter. According to Ohm’s, law,, , V=IR,, , Where,, , Potential difference, v=6V, , Current flowing through the circuit/resistors =, Resistance of the circuit, R=5+8+12=250, 1 = V/R = 6/25 =0.24A, , Potential difference across 12 9 resistor = Vi, Current flowing through the 12 Q resistor, /=0.24A, Therefore, using Ohm’s law, we obtain, , Vi =IR=0.24x12=2.88 V, , Therefore, the reading of the ammeter will be 0.24 A., The reading of the voltmeter will be 2.88 V.

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Page No: 216, , 1. Judge the equivalent resistance when the following are connected in parallel — (a) 1 Qand, 10£Q, (b) 1 Q and 1029 and 1062., , Answer, , (a) When 1 Q and 10® Q are connected in parallel:, Let R be the equivalent resistance., , , , a a i, ~— = -— 4+——}, R a ee, 6 6, 10 10, R=——_— = —=-102, 1+10 10, Therefore, equivalent resistance =1Q, (b) When 1Q, 103 Q and 106 Q are connected in parallel:, Let R be the equivalent resistance., a = # a 106+ 107+1, ee ee ee, R a p= 18° 10°, 1000000, >= —__—__ > 0.999 4), 1001001, , Therefore, equivalent resistance = 0.999 Q, , 2. An electric lamp of 100 O, a toaster of resistance 50 Q, and a water filter of resistance 500 Q, are connected in parallel to a 220 V source. What is the resistance of an electric iron connected, to the same source that takes as much current as all three appliances, and what is the current, , through it?, Answer, , Resistance of electric lamp, Ri = 100Q, Resistance of toaster, R2=50Q, , Resistance of water filter, Rz3 = S0OOQ, Potential difference of the source, V= 220 V, , These are connected in parallel, as shown in the following figure., R, = 1002, , , , , , , , , , , , , , =, =soQ, —, R3— 5002, A tw —, i]!], vV=220V, , Let R be the equivalent resistance of the circuit.