# Resistance , current and temperature

1. Feb 27, 2009

i have a question and i will be glad if anyone could help

you know if a current flow in resistance , a power is consumed =(I^2)*R

and if this current flows for an hour , this will produce energy and it's quantity is watt*hour

my question is , if the temperature of the resistor was 20 degrees at the start ( time=zero)

after 1 hour what will be the temperature

2. Feb 27, 2009

### Mapes

Hi adool_617, welcome to PF. The temperature depends on a couple important factors:

- The specific heat of the resistor material, which connects dissipated energy to temperature change.
- The heat transfer details of the system (conduction, convection, and radiation), which govern the rate that energy is removed from the resistor.

3. Feb 27, 2009

### Naty1

I agree with the answer provided....that question is asked here regulalry,,,it's NOT simple...

for a really rough cut approximate answer you could convert watts to BTU's and if you know the specific heat of the resistor do a crude calculation...a kwh is about 3413 BTU's....
pick some specific heat fropm a physics book or http://en.wikipedia.org/wiki/Specific_heat#Table_of_specific_heat_capacities

Maybe use tungeston as a surrogate....

But the problem with this approach is that likely a resistor is an internal resistance material analogous to tungestion, coated with ceramic....and that will change the heat disipation characteristics, perhaps dramatically.

And once the resistor begins to heat, convection begins which slows subsequent temperature rise...just as if a fan were applied...