Question

Two bulbs A and B are rated 9W and 18W respectively, at 18V. If these bulbs are connected in series with a 18V supply then the power of bulb A is --------W [ Don't write unit. ]

Answer 1

Explanation:

Power consumed in one bulb rated as P

1

W,Vvolt having resistance of R

1

Ω is

P

1

=

R

1

V

2

.........(1)

For certain number of bulbs we can write,

P

2

=

R

2

V

2

.........(2)

P

3

=

R

3

V

2

and so on..........(3)

We know in series combination resistances get added, hence

R

eq

=R

1

+R

2

+R

3

+...........

dividing both sides by V

2

, we get

V

2

R

eq

=

V

2

R

1

+

V

2

R

2

+

V

2

R

3

+........

Referring equations (1),(2) and (3)

P

eq

1

=

P

1

1

+

P

2

1

+

P

3

1