Two lamps can be connected to a battery in a circuit in series or in parallel. You can calculate the total resistance RT (t is down from r) in a circuit if you know the resistance in each lamp. Resistance is measured in ohms. For a circuit connected in series, RT = R1 + R2. For a circuit connected in parallel, 1/RT = 1/R1 + 1/R2.

Question

a. The lamps are connected in parallel. RT = 12 ohms. Find R2.

Answer 1

just plug it into the formula:

1/12 = 1/R1 + 1/R2
Unless you know R1, you can't figure R2. If the lamps are identical, then R1=R2=24

Answer 2

I'm sorry, R1 = 30 ohms.

Answer 3

How do I do 1/12 = 1/30 + 1/R?

Answer 4

1/R = 1/12 - 1/30
1/R = 1/20
R = 20