A light uncharged metallic sphere suspended from a thread is attracted to a charged rubber rod. After touching the rod the sphere is repelled by the rod. Explain
Answers
"A light, uncharged metallic sphere suspended from a thread is attracted to a charged rubber rod. After it touches the rod, the sphere is repelled by the rod. Explain."
Explanation :
charges are free to move (that wouldbeelectrons in metal).
uncharged means that there is same number of positive and negative charges so they cancel each other.
when sphere is placed near charged object, free charges in sphere move towards or away from side facing charged object. if the rod is charged positive, electrons in sphere would be attracted to it.
if the rod is negative, electrons would be repelled (but either way they cannot get away from sphere).
this movement of electrons on the sphere when near charged object causes dipole effect (one side of the sphere is positive and other is negative). side with excess electrons is negative, side with shortage of electrons is positive. both sides of dipole have equal charge but since one of them is closer to rod, that force is stronger. net effect if attractive force dominates (regardless if rod charge is positive or negative).
once sphere and rod make contact, some of the charge will move from rod (charged) to sphere (was not charged). now both of them are charged with same type (positive or negative charge) and so they repel