# Homework Help: Radiation: Net Heat Flow

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1. Jun 19, 2017

### lonelypancreas

1. The problem statement, all variables and given/known data
What is the net heat flow of an aluminum disk (emissivity = 0.05) with radius
10 cm and temperature 293K placed inside a room where the temperature is 300K?

Asurface = π*r2 = 0.01π m2
2. Relevant equations

3. The attempt at a solution
By simply plugging in the values, I get a value of 0.13. However, the answer is not among the choices.

Where did I possibly go wrong?

2. Jun 19, 2017

### collinsmark

That's the numerical answer that I got (don't forget to include your units in the future), with the possible exception of a negative sign.

What are the other choices?

3. Jun 19, 2017

### lonelypancreas

4. Jun 19, 2017

### collinsmark

Hmm. The given answer choices differ from our answer by a factor of around √2, for what that's worth.

Unless there's more to the problem though I think our answer of 0.13 W is correct*. I don't know, maybe it's a mistake in the book/coursework?

*I'll let you figure out if it's into or out of the disk.