# Physics Problem Please help?

Please help me with this physics questions

I am finding the resistance for a parallel circuit and it wants me to find the formula for total resistance using Ohm's Law, V=IR (be specific with the correct subscripts - ie. V1 = I1R1 would represent the voltage across R1 precisely)

### 3 Answers

- electron1Lv 71 year agoFavorite Answer
When resistors are in parallel, the following equation is used to calculate the equivalent resistance.

1/Req = 1/R1 + 1/R2

As an example, let R1 be 40 Ω and R2 be 20 Ω.

1/Req = 1/40 + 1/20 = 3/40

Req = 40/3 = 13⅓ Ω

Let’s assume the two resistors are attached to a 12 volt battery. Let’s use the following equation to calculate the total current.

V = I * R

12 = I * 13⅓

I = 0.9 amp

In a parallel circuit, the voltage is the same for each resistor.

For the 40 Ω resistor, I = 12 ÷ 40 = 0.3 amp

For the 20 Ω resistor, I = 12 ÷ 20 = 0.6 amp

In a parallel circuit, the total current is equal to the sum of the currents in each resistor. I hope this is helpful for you.

- oldschoolLv 71 year ago
Share the complete question including the circuit and you will get much better answers.

- L. E. GantLv 71 year ago
The two possibilities are

the circuits in series, in which case, the R is the total of all the resistor.s

so if you had 1 10 ohm and 1 20 ohm resistor, the total resistance would be 30 ohm

For parallel circuits: use !/R = 1/r1 + 1/r2 + 1/r3 +....... 1/rn

So for a 10 and a 20 in parallell,

1/R = 1/10 + 1/20 = 3/20

so R = 20/3 ohm