# Thermodynamics: Change in Entropy

1. Mar 11, 2008

### djaymilla

1. The problem statement, all variables and given/known data

A 50-ohm resistor carrying a constant current of 1 A is kept at a constant temperature for 27 deg. C by a stream of cooling water. In a time interval of 1s, (a) What is the change in entropy of the resistor? (b) What is the change in entropy of the universe?

2. Relevant equations

dS = dQ / T
dQ = C dT

3. The attempt at a solution

For part a, I understand that the dQ of the resistor is zero because there is a constant temperature and current.

For part b, I do not understand the relationship between resistance (50 ohm), and dQ. I arrive at the correct answer by plugging in 300K (27 deg C) in for T, and 50 ohm in for dQ, but I would like to understand the correct relationship. Any help?

2. Mar 11, 2008

### Mapes

Power generation (the amount of energy dissipated per second) is calculated as $I^2R$.