Question

A 0.10 W bulb and a 0.90 W bulb are connected in series to a 12-volt power supply.

(a) What is the power delivered to the first bulb?

W

(b) What is the power delivered to the second bulb?

W

(c) Which bulb is brighter?

Bulb 2

Bulb 1    

Both are equally bright

(d) What is the total power delivered by the battery?
W

Answer 1

When connected in series: In a series connection, current flowing across each element is same. So when 0.10W bulb and 0.90W bulb are connected in series, same current will flow through them. To find which bulb will glow brighter we need to find the power dissipation across each of them. From the relation

P=(I*I) R

a) the power delivered to the first bulb 0.10 W

b) the power delivered to the first bulb 0.90 W

c) Bulb 1. since current is same we can say that power dissipation will be higher for the bulb with higher resistance i.e. 0.10W bulb.

Hence 0.10W bulb will glow brighter in series connection.

d) total power delivered by the battery 1 W