Question

A rod is brought near an uncharged pith ball electroscope. What conclusion would you draw about the charge on the rod if the pith ball moves towards the rod?
A. Uncharged
B. Charged
C. Neutral
D. Can’t say

Answer 1

Hint: Pith ball is a device used to measure the presence of charges and the polarity of the charges. Electrostatic induction is the reason behind the movement of the pith ball towards the rod. The basic principle of attraction of opposite charges and repulsion of like charges can be used here to understand the question.

Complete Step-by-Step solution:
Pith ball electroscope is a device that can be used to find the polarity of an unknown charge and study about the static electricity. The charge of a pith ball can be a static charge, either positive or negative according to the charge of the body that we are using.
As we know, in electrostatics, the like charges will repel each other and unlike charges will attract each other. Like charges means both charges are of the same kind while unlike charges means one of charge has to be positive and the other one will be negative.
In this question the pith ball is uncharged. When we are approaching the pith ball with a rod, then we can observe that pith ball moves towards the rod. From this, we can say that the rod is charged one. If the rod is negatively charged material, then the electrons within the pith ball reorient themselves to move away from the negatively charged rod. This creates an imbalance of charges on the pith ball. There is a net positive charge accumulation on the side closest to the charged rod and negative charge on the opposite side. This is the reason for the attraction between rod and pith ball. Here we can’t find any contacts between them. Thus, there is no actual transfer of electrons. This is a temporary arrangement and this is known as electrostatic induction. Here, the charged rod induces charges on the pith ball. This temporary arrangement will return to the normal state when the rod is removed. If we are using a positively charged rod, then it will induce a negative charge on the pith ball which is closest to the rod. So the correct answer is option B.

Note: If the negatively charged rod touches the neutral pith ball, an electron flow can be established. Electrons from the rod move to the pith ball and give an excessive amount of negative charges. This is simply known as electrostatic conduction. Since the rod and pith ball is negatively charged, they will repel each other. The induced and conducted charges will be opposite if we are using a charged rod (either positive or negative). If we are using an uncharged or a neutral, it can’t make any movement to pith ball. Since pith ball is also neutral.