Q. 283.8( 21 Votes )

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?

Answer :

(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


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