Question

Question No. 15
Three identical electric bulbs A, B and C are connected as shown. What changes occur in brightness of the bulbs, when the switch is closed?
A
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Answer 1

Brightness of bulb  A increases while of bulb  B decreases

This is because:

Assuming resistance and voltage through terminals of the  bulbs to be V and R, initially total resistance of the circuit is 2R.

Current flowing through them is equal, I=V/2R

When the switch gets closed, the total resistance of circuit is equal to 1.5 R

Current flowing through A= 2V/3R

Current flowing through B=V/3R

Hence as current through A increases, brightness of Bulb A increases while as current through B decreases ,brightness of bulb B decreases.

Answer 2

Answer:

Brightness of A increases and that of B decreases.