There is quite confusing question most of the time asked in
interview is that if there are three bulbs having ratings as 60W, 30W and 20W
and these bulbs are connected in parallel then which of these bulb will be
brightest??

Answer to that question is that in Parallel

__1__=

__1__+

__1__+

__1__

R(eq)
R1 R2 R3

Multiply both sides by Rated voltage square i.e. (V

_{ Rated})^{2}
We get

__(V__=

_{ Rated})^{2}__(V__+

_{ Rated})^{2}__(V__

_{ Rated})^{2 }^{ }+

__(V__

_{ Rated})^{2}
R(eq) R1 R2
R3

This means

P(eq)= (P1)+(P2)+(P3)

^{}
This means in Parallel Power will be additive

In series we get

R(eq)= R1 + R2 + R3

Now divide both sides by (V

_{ Rated})^{2}
We get

__R(eq)__=

__R1 + R2 + R3__

(V

_{ Rated})^{2 }(V_{ Rated})^{2}
Thus we get

__1__=

__1__+

__1__+

__1__

P(eq) P1 P2
P3

**Thus we see that when all bulbs are connected in Parallel then 60W i.e. highest rating will be brightest and when all bulbs are connected in series then bulb with lowest rating i.e. 20W will be brightest.**