Question

what is the branch of physics which deals with current electricity? which charge is occupied by balloon when rubbed by wall?

Answer 1

The branch of physics dealing with charges in motion is called current electricity and we study it in electronics.
Suppose a negatively charged balloon is held near a neutral object such as a wall, the charges in that object move. Since like charges repel each other, the electrons in the wall move as far away from the balloon as possible. Thus, there are more positive charges closer to the negatively charged balloon. And since opposite charges will attract each other, the opposite charges of the balloon and wall will attract one another.