Two bulbs consume same energy when operated at 200 V and 300 V, respectively. When these bulbs are connected in series across a dc source of 500 V, then
P=V2R or R=V2P or R∝V2,
i.e., R1R2=(200300)2=49.
When connected in series, potential drop is in the ratio of their resistances. So, V1V2=R1R2=49
Now, P=I2R Or P∝R (in series I is the same)