Q42 of 72 Page 12

Five dry cells each of 1.5 volt have internal resistance of 0.2, 0.3, 0.4, 0.5 and 12 ohms. When connected in series, what current will leave these five cells furnish through 10 ohm resistance?

Total voltage produced by the batteries V = 5 × 1.5 = 7.5 VTotal resistance R = Internal resistance + external resistance
                         = (0.2 + 0.3 + 0.4 + 0.5 + 1.2) + 10 = 12.6 Ω
Therefore current I = = 0.595 A.

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40 In the circuit shown in figure below, calculate (i) the current flowing through the arms AB, AC and CDE; (ii) the potential difference across AB, CD and DE. 41 A 40 watt lamp requires 0.182 A of current at 220 volts, while a 60 watt lamp requires 0.272 A of current at 220 volts. If a 40 watt lamp and a 60 watt lamp are connected in series with a 220 volt line, how many amperes of current will flow through each lamp? 43 The value of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below:
I (amperes) 0.5 1.0 2.0 3.0 4.0
V (volt) 0.5 2.5 6.75 11.0 15.0. 44 Calculate the resistance of one metre of copper wire that has a cross–sectional area of about 2 x 10-2 cm2 (using the value of resistivity of copper to be 1.2 × 10-8 ohm m) Compare the value of this resistance with that of a flashlight bulb, which has a power rating of 1 W and operates at 3 V. What does this comparison tell you ?