Q28 of 35 Page 93

B1, B2 and B3 are three identical bulbs connected as shown in Figure 12.8. When all the three bulbs glow, a current of 3A is recorded by the ammeter A.


(i) What happens to the glow of the other two bulbs when the


bulb B1 gets fused?


(ii) What happens to the reading of A1, A2, A3 and A when the


bulb B2 gets fused?


(iii) How much power is dissipated in the circuit when all the


three bulbs glow together?

(i) There will be no effect on glow of other two bulbs and will remain same when B1 gets fused because glowing of bulb depends on power and the potential difference and resistance remains same of other two bulbs.


(ii) When there are parallel connections:


Net resistance will be 1/R = 1/R1+1/R2+1/R3


Since resistance is same so, R’ = R/3


Applying ohm’s law V= IR


R =4.5Ω


Since B2 gets fused, so now only two bulbs B1 and B3 are in parallel


Therefore net resistance in parallel 1/R’ =2/R


R’ = 4.5/2 Ω


I = V/R’ = 2×4.5/4.5


I = 2A


So, current will be distributed in both the bulbs as 1 A each.


(iii) Power dissipated when all three bulbs glow together


P = V × I


P= 4.5 × 3 = 13.5 W


More from this chapter

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26

A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 Ω when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 Ω is connected in parallel with this series combination, what change (if any) in current flowing through 5 Ω conductor and potential difference across the lamp will take place? Give reason.

 27

Why is parallel arrangement used in domestic wiring?

 29

Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source.

(a) Will the bulb in the two circuits glow with the same brightness? Justify your answer.


(b) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.

 30

State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.