# A Surface Integral of a Scalar Field with Time Dependency

Tags:
1. Feb 15, 2017

### mohamedibr752

Can someone explain to me how this solution is obtained ?

I mean the last part that applied divergence theorem ?

For example, in the x-direction, why did we substitute x with t and took the derivative of t w.r.t. t ?!

Can someone explain it physically as well ?

What does it mean to have a surface specified with x = 0 & t ?