Suppose the maximum safe average intensity of microwaves for human exposure is taken to be 2.50 W/m2. If a radar unit leaks 10.0 W of microwaves (other than those sent by its antenna) uniformly in all directions, how far away must you be to be exposed to an average intensity considered to be safe

Since the surface area of the sphere of radius 'r' is given by 4πr² the intensity of microwaves at distance 'r' can be determine by using

I (r) = P/S

Where

P is power and it is given as P = 10W

'S is the surface area S=4πr²

I is intensity and it is given as

I = 2.5W/m²

Then,

I = P/S

I = P/4πr²

Ir² = P/4π

r² = P/4Iπ

r = √ (P/4Iπ)

r = √ (10/4π*2.5)

r = √0.3183

r = 0.564m

You must be 0.564m far away for safety against been exposed to radiation.