Question

two bulbs A and B are rated 100w-120v and 10w-120v. they are connected across a 120v source in series. which will consume more energy

Answer 1

It can be solved with power formula

Power = V^2/r where
Power is Watt, V is Volt and r is resistance.
in above question volt and watt is given and therefore we can calculate resistance first and then current for given bulbs

For first Bulb of 100 watt and 120 volt
according to formula Power = V^2/r
100 w = 120V^2/r
r = 120^2/100 = 14400/100 = 144 ohm
Now we have volt and resistance of bulb is available we can calculate current consumed by bulb by formula I = V/R where I is current, V is volt and R is resistance in ohm
accordingly, for first bulb the current is
I = 120/144 = 0.833 A

Similarly we can calculate the current for second bulb having rating 10w and 120 volt
resistance = 120^2/10 = 14400/10 = 1440 ohm
current = 120/1440 = 0.0833 A

From the above it can be see that bulb rating 100w - 120v is consuming more energy = Ans