Page 1 of 1

9.1

Posted: Fri Mar 16, 2018 8:06 pm
by Angela 1K
I guess this just proves how much I've forgotten about old material, but I'm having trouble on 9.1

The question asks the find at what rate does your body heat generate entropy in your surroundings, taken to be at 20. C? The body generates heat at a rate of about 100. W (J/s)

I can't seem to figure out why the equation is
rather than


And furthermore, in the solutions manual, the answer suddenly becomes positive.

Any help would be greatly appreciated! Thanks

Re: 9.1

Posted: Fri Mar 16, 2018 8:24 pm
by Ishan Saha 1L
Hi! Because it asks for the rate your body generates heat "in your surroundings" the formula has a -q. This because the system is releasing heat into the surroundings, or heat is flowing out of the system (with the system being the body).

Re: 9.1

Posted: Fri Mar 16, 2018 8:25 pm
by Angela 1K
Ishan Saha 1L wrote:Hi! Because it asks for the rate your body generates heat "in your surroundings" the formula has a -q. This because the system is releasing heat into the surroundings, or heat is flowing out of the system (with the system being the body).

That makes sense, but then why is the final answer positive if there's a negative component in the fraction?

Re: 9.1

Posted: Fri Mar 16, 2018 8:47 pm
by Nisarg Shah 1C
That is because the system is releasing heat, so it should be -q/t for the system, and positive q/t for the surroundings since they are absorbing heat.

Re: 9.1

Posted: Fri Mar 16, 2018 9:00 pm
by Mitch Walters
There is a negative because of the fact that the heat is leaving your body and going into the surroundings.

Re: 9.1

Posted: Sat Mar 17, 2018 2:00 am
by Rishi Khettry 1L
Heat is leaving the body so you regard the body as the "system" and therefore q is negative