Light Bulb question--SIMPLE!?

Question

I thought this was simple..but I think I don't fully understand circuits..can someone please help!?

"A" is a light bulb that uses 14.0 watts when connected across a 60 volt battery. "B" is a light bulb that uses 27.0 watts when connected across a 60 volt battery.

(a) "A" and "B" are connected in series across a 60 volt battery. What is the total power?

(b) "A" and "B" are connected in parallel across a 60 volt battery. What is the total power?

Answer 1

you need to know the resistance (R), and the current (I) drawn by each bulb.

using Power, P = VI and V = IR,

for bulb A: I = 14.0/60 = 0.233A and R = 257.14 ohms

for bulb B: I = 27.0/60 = 0.45 A and R = 133.33 ohms

(a) When connected in series, the total resistance of both bulbs is 257 + 133.3 = 390.47 ohms

so the current I drawn is 60/390.47 = 0.154A.

Therefore the total power = VI = 60 X 0.154

= 9.22W (ans)

(b) When connected in parallel, total power drawn =

14.0 + 27.0 = 41.0W (ans)