Please help I will rate!! In a common physics demonstration, a rubber rod is fir
ID: 1733447 • Letter: P
Question
Please help I will rate!! In a common physics demonstration, a rubber rod is firstedrubbed vigorously on silk or fur. It is then brought close to asmall styrofoam ball, which it attracts. If you then touch the ballwith the rod, it suddenly repels the ball. Why does it firstattract the ball, and why does it then repels the same ball? Is it because when we touch with our hands it neutralize thecharge between the silk/fur to the rubber rod?? thanks in advance! Please help I will rate!! In a common physics demonstration, a rubber rod is firstedrubbed vigorously on silk or fur. It is then brought close to asmall styrofoam ball, which it attracts. If you then touch the ballwith the rod, it suddenly repels the ball. Why does it firstattract the ball, and why does it then repels the same ball? Is it because when we touch with our hands it neutralize thecharge between the silk/fur to the rubber rod?? thanks in advance!Explanation / Answer
The charges are free to move,the charge at a point on the conductor would respond to the force by moving toward the surface.Clearly,then a uniform distribution of charge within the sphere's volume is not in equilibrium.In fact,the argument that a charge at the point will move toward the surface can be applied to any charge within the sphere.Excess sharge placed on a conductor,whether positive or negative,moves to the exterior surface of the conductor.When an excess charge is applied to such a conductor,all the charge ends up on the exterior surface,and none on the interior surfaces.Because the positive ions in the metal do not move,the field tends to move negative charges to the left and leave excess positive charges on the right;hence,it causes the ball to have an induced negative charge on its left half and an induced positive charge on its right half. Therefore,the rubber rod first attracts the ball and when the rod is touched,the rod becomes neutral and hence the rod repels the same ball.