question_answer 69)

  and  three identical bulbs connected as shown in figure. 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 gets fused? (ii) What happens to the reading of and A when the bulb  gets fused? (iii) How much power is dissipated in the circuit when all the three bulbs glow together?

Answer:

                  Resistance of combination of three bulbs in parallel If R is the resistance of each wire then or            Current in each bulb,  (i) When bulb , gets fused, the currents in B2 and B3 remain same, becausevoltage across the B2 and B3 bulb remains same, so their glow remains unaffected. (ii) When bulb gets fused, the current in becomes zero and current in  and remains 1A. Because voltage across and  bulb remaining same Total current      Current in ammeter, Current in ammeter, Current in ammeter, Current in ammeter, (iii) When all the three bulbs are connected. Power decapitated,