question_answer 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 .                 (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?  

Answer:

(a) Usingwe get                                 .                 (b) No, it cannot be said so because there may be equal number of positive and negative elementary charges inside the box. It can only be said that net charge inside the box is zero.