# Resistive dissipation and Ohm's law

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1. Jun 8, 2017

1. The problem statement, all variables and given/known data
A potential difference V is connected across a device with resistance R, causing current i through the device. Rank the following variations according to the change in the rate at which electrical energy is converted to thermal energy due to the resistance, greatest change first:
(a) V is doubled with R unchanged,
(b) i is doubled with R unchanged,
(c) R is doubled with V unchanged,
(d) R is doubled with i unchanged.

2. Relevant equations
$$P= {i^2} R$$
$$P= \frac {V^2} R$$

3. The attempt at a solution
I know and understand that (a) and (b) result in $P'=4P$, but I'm not sure if I judge (c) and (d) variations correctly. I guess that the answer to (c) and (d) is that there would be no change if the device obeys Ohm's law.

2. Jun 8, 2017

### cnh1995

You can assume some values for V and R and check each condition. You have listed the correct equations.
No change in what?

3. Jun 8, 2017

No change in $P$.

4. Jun 8, 2017

### cnh1995

There will be changes in P according to the equations you've listed.

5. Jun 8, 2017