Q 1.17)

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 8.0 × 10 3 Nm2/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?

 


 
(a) Net outward flux through the surface of the box, φ= 8.0×103 Nm2/C
 
For net charge q inside the box,

ϕ=qε0
q=ε0ϕ=8.854×1012×8.0×103C=7.08×108C=0.07μC
Therefore, the net charge inside the box is 0.07 uC.

(b)

The net flux through a body depends on the net charge inside the body. If the net flux is zero, then it can be inferred that the net charge inside the body is zero. The body may have an equal amount of positive and negative charges.