First slide

Thermal effect of current

Question

A 25 W-120 V bulb and 100 W – 120 V bulb are connected in series across 120 V line. Which bulb will be brighter ?

Easy

A

25 W – 120 V
B

100 W- 120 V
C

Both will have same incandescence
D

neither will give any light

Solution

$R_{1} = \frac{{(120)}^{2}}{25} a n d R_{2} = \frac{{(120)}^{2}}{100} ∴ R_{1} {>R}_{2} A l s o, P_{1} {=i}^{2} R_{1} {and P}_{2} {=i}^{2} R_{2} (bulbs in series means same current) ∴ P_{1} {> P}_{2} The bulb which consumes more power glows brighter$

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