Question

A charged rod is brought near a negatively charged pith ball electroscope. What conclusion would you draw about the charge on the rod if the pitch ball moves away from the rod?
A) Positive
B) Negative
C) No charge
D) Can’t say

Answer 1

Hint: In the field of electrostatics, like charges are said to repel each other and unlike charges are said to attract each other. Like charges refers to charges that are of the same kind (either positive or negative) and unlike charges refers to the charge that is of the opposite kind (one positive and one negative).

Complete step by step answer:
A pith ball electroscope is a device that is used to determine the polarity of an unknown charge. The pith ball can be given a static charge, either positive or negative by touching it with a positively or negatively charged body respectively.
In the field of electrostatics, like charges are said to repel each other and unlike charges are said to attract each other. Like charges refers to charges that are of the same kind (either positive or negative) and unlike charges refers to the charge that is of the opposite kind (one positive and one negative).
In the question, it is given that a charged rod is brought near a pith ball electroscope and the pith ball moves away from the rod that is repelled by the rod. Since the pith ball is negatively charged, is repelled by the rod, and since charges repel each other, it can be concluded that the charge on the rod is negative.
Thus, the rod is negatively charged.

So, the correct answer is B) Negative.

Note: A simple experiment to understand further that like charges repel and unlike charges attract is by the use of a glass rod and silk cloth. If we rub the glass rod with the silk cloth, the glass rod becomes positively charged as the silk cloth quickly takes away the electrons.
This is the process of transfer of charges from one system to another. This happens due to the flow of electrons. One body takes electrons from the other body becoming negatively charged while making the other body positively charged. However, the total net charge in both of the bodies combined is not changed since by the fundamental principle of conversion of charge, the charge can neither be created nor destroyed, it can only be transferred from one body to another.
After this, if the glass rod is brought near some pieces of paper, the pieces of paper jump up and stick to the glass rod. This happens because the negative charge rod attracts the positive charges in the paper to the side near the rod and this uneven force causes the pieces of paper to jump up and stick to the rod.