Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is `8.0xx10^(3) Nm^(2)//C` (a) what is the net charge inside the box ? (b) If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box ? Why or why not?

Explanation

We can use Gauss.s law to find out the net enclosed charge within the box.
`phi=q_("in")/epsilon_(0) rArr q_("in") =phi xx epsilon_(0)`
`=8xx10^3xx8.85xx10^(-12)=70.9xx10^(-9)`
`=70.9xx10^(-9)=0.071 muC`
(b) If the net outward flux is zero then we can only say that the net charge enclosed inside the box must be zero too. It is possible that there are charges inside box but they cancel each other. It is also possible that there is no charge at all inside the box.