Question

How much heat is produced by a human body?

(a) 200 W

(b) 100 W

(c) 50 W

(d) 0.5 W

I had been asked this question in an online interview.

Question is taken from Basic Energy Concepts topic in chapter Energy Balance of Bioprocess Engineering

Answer 1

The correct choice is (b) 100 W

For explanation: A man doing no or very little physical work needs about 2,000 kcal (or less) of energy in his daily food. The body converts this energy almost entirely into heat.

1 day = 24 x 60 x 60 s = 86,400 s 1 cal = 4.2 J

Hence, 2000 kcal/day = 2000 × 4.2 kj/day = \(\frac{8.4 \,Mj}{86600s}\)

= 100 j/s = 100 W

We see that a human body doing no work is equivalent to a heat source of about 100 W – the equivalent of a good bulb.