# Homework Help: Rate of heat radiated from a person

1. Apr 19, 2007

### Hendrick

1. The problem statement, all variables and given/known data
What is the percentage increase in the rate of heat radiated from a person with a surface skin temperature of 34.0 °C compared with the same person with a skin temperature of 33 °C?

2. Relevant equations
Stefan's Law of emission:
P = σAeT^4

- P = rate of energy transfer (Watts)
- σ = 5.6696 x 10^–8 W m^–2 K^–4
- A = surface area of the object
- e = emissivity (varies from 0 to 1)
- T = temperature (Kelvins)

3. The attempt at a solution

(34+273)^4/(33+273)^4
= 1.013 % (3sf)

2. Apr 19, 2007

### Hootenanny

Staff Emeritus
That isn't a percentage, thats a ratio. You need to multiply by 100 to obtain a percentage.

3. Apr 19, 2007

### Hendrick

Oh, thanks lol.

Is this right:-

(34+273)^4/(33+273)^4 * 100
= 101.3136113 %

the increase being:
= 101.3136113 % - 100
= 1.3136113%

4. Apr 19, 2007

### Hootenanny

Staff Emeritus
Looks good to me