Questions
If X, Y and Z in figure are identical lamps, which of the following changes to the brightnesses of the lamps occur when switch S is closed?
detailed solution
Correct option is B
When switch is open :
X and Y lamps are in series.
Power dissipated in the bulbs is
and current i is
When switch is closed :
Y and Z are in parallel, their effective resistance is R/2.
X and YZ combination are in series, and effective resistance becomes 3R/2
Current in the circuit is
P.d across Y-Z combination is
Therefore brightness of X increases and Y decreases.
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