# Homework Help: Energy Dissipation Across a Resistor

1. Jul 7, 2012

### boredbluejay

1. The problem statement, all variables and given/known data
A battery is connected across a uniform resistor R0. A sliding contact can move across R0 from x=0 to x=10cm at the right. Moving the contact changes how much resistance R is to the left of the contact and how much is to the right. Find the rate at which energy is dissipated in R as a function of x.

2. Relevant equations
Energy dissipated: PR=i2R
Voltage is the same for resistors in parallel
1/Rtotal=1/R+1/R0
itotal=V/Rtotal

3. The attempt at a solution
I tried to express R in terms of x and R0, but I got stuck. I honestly have no idea how to begin, or even if all of the equations that I wrote above are relevant to this question. Could someone please give me a hint that'll point me in the right direction? Thanks!

2. Jul 8, 2012

### tiny-tim

hi boredbluejay!

isn't resistance proportional to length?

3. Jul 8, 2012

### boredbluejay

I guess, but by what factor. >< I'm sorry, I'm really bad at this.

4. Jul 8, 2012

### lewando

You have two points on the x,R plane: (0,0) and (10,R0). With this, determine the linear relationship R = mx + b.