# Stefan's law Understanding

1. Nov 27, 2007

### neelakash

Do all incandescent solids obey the fourth power law of temperature?

I think they all obey $$\ T^4$$
But the constants are different for them.

Agreed?

2. Nov 27, 2007

### Shooting Star

Are you saying that for a particular object, the "constant" remains constant for T=0 to infinity? What logical basis have you for such a conjecture? (Of course, it may not be a conjecture, may be an actual law -- that's what we're discussing here.)

3. Nov 27, 2007

### neelakash

Stefan's constant $$\sigma$$ has the same value for all temperatures and all bodies.

But the actual law is $$\ I=$$ $$\epsilon$$$$\sigma$$$$\ T^4$$

where $$\epsilon$$ is the emissivity.

I think $$\sigma$$ is constant for all but $$\epsilon$$ varies.

Last edited: Nov 27, 2007
4. Nov 28, 2007

### Shooting Star

You are correct: sigma is a universal constant.

For the same body, the emissivity may vary with temperature. So, I = e*sigma*T^4 actually becomes meaningless practically if e varies too much with T for a given body.