# Finding the potential difference across two wires

#### SamS90

Hello everyone, as you can tell I'm new and just wondering if I could get some help with this question as I'm not sure where exactly I've gone wrong:

1. Homework Statement

Two wires are used to connect a lamp to a power supply of negligible internal resistance. The potential difference across the lamp is 12V and its power is 36W. Calculate the potential difference across each wire. The two wires in question are made of copper and have a resistivity of 1.7 x 10^-8 Ohm meter.

2. Homework Equations

Not 100% sure but:

V=W/Q, R=V/I, I=P/V, E= I (R + r)

And I'm not sure about an others.

3. The Attempt at a Solution

I = 36/12, I = 3
R = 12/3, R = 4
E = 3 (4 + 1.7x10^-8) = 12V

Therefore the potential difference across each wire is 12V

I know I've gone wrong some where and am hoping someone can put me right.

Many thanks,
Sam
1. Homework Statement

2. Homework Equations

3. The Attempt at a Solution

Related Introductory Physics Homework Help News on Phys.org

#### Doc Al

Mentor
3. The Attempt at a Solution

I = 36/12, I = 3
Good. You found the current, which you'll need.
R = 12/3, R = 4
That's the resistance of the lamp. OK, but not needed.
E = 3 (4 + 1.7x10^-8) = 12V

Hint: What's the resistance of each wire? How long are they?

#### SamS90

Thanks for the help.

Using 0.6m as length and 0.001m as the cross sectional area I have derived an answer of 3.06 x 10^-5 after first findinng the resistance of both wires (as you stated) then using the resistance found in the equation V = IR to find the potential difference.

Thanks again.

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