The question is incomplete! circuit figure is attached below and answer and explanation is provided below.
Answer:
Bulb_A = Bulb_B = Bulb_D and Bulb_C = 0.
Explanation:
What happens when switch is open?
When the switch is open Bulb_C is open circuited meaning that there is no way for the current to flow through it. This path offers infinite resistance to the current therefore, current will try to take a least resistance path that is through Bulb_B.
So eventually, when the switch is open the circuit becomes a simple series circuit with path From battery to Bulb_A to Bulb_B to Bulb_D to battery with Bulb_C = 0.
What happens in a series circuit?
We know that in a series circuit, there is only one path for the current to flow therefore, same current will flow through all the series Bulbs and their brightness will be same. Bulb_A = Bulb_B = Bulb_D
Brightness in a series circuit:
We also know know that in a series circuit, resistance gets summed up and voltage across each Bulb gets shared which results in less power dissipation that's why Bulbs connected in series appear dimmer as compared to when they are connected in parallel.
