Chapter 16, Problem 8Q

Figures 16-7 and 16-8 show how a charged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

To determine

The reason that by placing a charged rod near an uncharged metal object, only some of electrons move.

Explanation of Solution

Introduction:

When a charged body says positive charge placed near an uncharged body, then the free electrons in the uncharged body attract towards the positive charge body. Initially, the uncharged body is neutral but after moving of some of its negative electrons the uncharged body acquires a net charge. This process is called charging by induction.

When a charged rod placed near an uncharged metal object, the uncharged metal object gets charged because of induction phenomenon. The free valence electrons in the uncharged metal object start move towards the charged body and generates potential difference in the uncharged body.

In the first figure, the electrons moves towards the end near the charged rod until the attractive force due to charged rod on the remaining electrons is balanced by the repulsive force of electrons gathered at left end.

In second figure, stationary rod is grounded. So, the electrons in it repelled by the negative charged rod and they leave to the ground until the attractive force due to the net positive charge on the stationary rod balances the repulsive force on the remaining electrons in the rod.