# Homework Help: The Rate at which kinetic energy changes to thermal energy

1. Apr 14, 2013

### Pruddy

A potential difference of 50 mV is maintained between the ends of a 9.70 m length of wire whose cross section area is 25.0mm^2. The conductivity of the wire is 6.80 x 10^6 (ohm.m)^-1. Determine the rate at which the energy in the wire is transformed into kinetic to thermal energy.

2. Relevant equations
P = v^2/R

ρ = 1/c

R = ρ (L/A)

Where ρ = resistivity
c = conductivity
A = area
L = length
R = Resistance
V = Voltage
P = power

3. The attempt at a solution

ρ = 1/6.80 x 10^6 = 1.471 x 10^(-7)

R = 1.471 x 10^(-7) * ( 9.70/0.000025 )
= 0.0570748
P = (50 x 10^-3)/0.0570748
= 0.0438021
= 4.38 x 10^(-2) W

This is my complete work. I think my workings are correct but My instructor says my answer is wrong. I will be glad if anyone can help.

2. Apr 14, 2013

### Staff: Mentor

Where do you have kinetic energy? I think this should be electric energy.

There is a ^2 missing at P=, but the following line is correct. Units are missing everywhere :(.
I would express the final answer in mW or W. I agree with the result, however.

3. Apr 14, 2013

### haruspex

This is a duplicate of post https://www.physicsforums.com/showthread.php?t=685309, 1 hour earlier, apparently just to change the title.
As mfb says, there's is no kinetic energy involved here, unless you mean thermal energy viewed as kinetic at the atomic level.