Question

The first answer is correct, I just don't know how to get the second part. Please help me

Suppose the maximum safe average intensity of microwaves for human exposure is taken to be 2.00 W/m^2. 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? Assume that the power spreads uniformly over the area of a sphere with no complications from absorption or reflection. What is the maximum electric field strength at this distance?

Answer 1

formula for the relation between Electric field E and Intensity I is

I = Emax^2/2uoC

so

Emax^2 = 2 I uo c

uo is 4pi e -7

c is 3e 8

so

Emax^2 = 2 * 2 * 4*3.14 *10^-7 * 3*10^8

Emax = 38.82 V/m or N/C