# Resistance with circuit

1. Aug 15, 2010

### JonJon

1. The problem statement, all variables and given/known data
Three 60 w 120 V bulbs are connected to a 120 V battery. 2 Bulbs are in parallel with each other in a smaller loop. The third is in series with the battery and the other loop.
find voltage difference across bulb three.

2. Relevant equations
R= V^2/P
1/R_loop= 1/R_1

3. The attempt at a solution
R=120^/60

1/R_total = 2/240 R_total= 120 +240 =360

I _total = V/R = 120/360

2. Aug 15, 2010

### Integral

Staff Emeritus
Start by finding the total circiut resistance.

You must have RT= RB+ RL

Were:
RB is the resistance of a single bulb and
RL is the resistance of the parallel pair of bulbs.

RL is :

$$\frac 1 {R_L} = \frac 1 {R_B} + \frac 1 {R_B}$$

So RL = .5 Rb

Now you should be able to complete the problem on your own.

3. Aug 15, 2010

### JonJon

I got V_3 is .33A * 240 = 80v but its -80v b/c its loosing right?