Question

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

1.  What happens to the glow of the other two bulbs when the bulb B₁ gets fused?
2. What happens to the reading of A₁, A₂, A₃ and A when the bulb B₂ gets fused?
3. How much power is dissipated in the circuit when all the three bulbs glow together?

 

Answer 1

Since all the three bulbs are identical so current through each bulb will remain same i.e 1 A

1. Even when bulb B₁ gets fused, other two bulbs will continue to glow with same brightness because all the three bulbs are connected in parallel so potential difference across each bulb remains same.
2. When bulb B₂ gets fused then the reading A₂ will become zero. The reading of A₁ and A₃ will remain same as 1 A because potential difference across them remains same. However, the reading of A will decrease and will become 2 A. 
3. Power dissipated by bulb B₁ will be
   P₁ = VI
   P₁ = 4.5 × 1
   P₁ = 4.5 W
   Similarly, 
   P₂ = 4.5 W
   P₃ = 4.5 W
   Hence total power dissipated by the circuit will be 
   P_net = P₁ + P₂ + P₃
   P_net = 4.5 + 4.5 + 4.5
   P_net = 13.5W