question_answer

(a) A current of 1 A flows in a series circuit containing an electric lamp and a conductor of  when connected to a 10 V battery. Calculate the resistance of the electric lamp. (b) Now if a resistance of  is connected in parallel with this series combination, what change (if any) in current flowing through  conductor and potential difference across the lamp will take place? Give reason. Or Three bulbs each having power P are connected in series in an electric circuit. In another circuit, another set of three bulbs of same power are connected in parallel to the same source. (a) Will the bulbs in both the circuits glow with the same brightness? Justify your answer. (b) Now let one bulb in each circuit get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason. (c) Representing each bulb by a resistor, draw circuit diagram for each case.  

Answer:

(a) Given, Current = 1 A, Potential difference Total resistance in the circuit                                 (1/2)  Conductor of  and lamp in series,                                                            (1) Potential difference across lamp                                                      (1/2) (b) When  resistance is connected in parallel with R, then total resistance R' in the circuit is given by                                                                     (1) Current through the circuit Since,  and R are in parallel,  Current through,                                                       (1) Thus, current through lamp and conductor of  in series is 1 A i.e., there is no change in current through conductor of .                                                      (1 /2) Potential difference across lamp  i.e., there is no change in potential difference across the lamp.                                         (1/2)                                                 Or (a) Bulbs in parallel provide more illumination because of the following (i) Each bulb gets same voltage and is equal to the applied voltage. (ii) Each bulb draws required current from the mains. Hence, they work properly.                                            (b) When one bulb in each circuit get fused, In series Rest of the bulbs will not glow. This is because in series arrangement, there is only a single path for the flow of current. In parallel Rest of the bulbs will continue to glow as in parallel. (i) Individual branch in the circuit completes its own circuit. (ii) Different paths are available for the flow of current.                                   (1 x 2) (c) Circuit diagram For series For parallel                        (1 x 2)