Question

Robert Millikan is famous for his experiment which demonstrated that electric charge is discrete, or quantized. His experiment involved measuring the terminal velocities of tiny charged drops of oil in air between two plates with a known voltage applied. He timed hundreds of them traveling both up and down in order to mathematically rule out the effects of gravity and drag, since he had no way of measuring mass or diameter. His results showed that charge comes only in integer multiples of 1.6 10 19C. This is called the elementary charge. It is the charge on both electrons, negative, and protons, positive.
1. a. Where does charge excess charge reside on an object? Why?
b. Where is electric charge more concentrated on irregularly shaped objects?
c. How do lightning rods work?
d. Why does a stream of water bend toward a charged object?
e. What are the three methods of charging an object?

Answer 1

1 a) the excess of charge reside on the surface of conductor because we know that electric field inside a conductor is always zero and hence the charges are pushed to the surface .

1 b) electric charge is more concentrated on sharp edges of an irregularly shaped objects due to the phenomenon known as Corona discharge, which states that the surface charge density is more at sharper points

1c) The lightening rod is a metallic conductor which allows an easy passage to flow of charges from the thunderbolt to the deep inside ground. Whenever, there is a storm or thunderbolt , the charges transferred to any building does not spread around the walls of the building and thereby giving shocks to people inside , but instead the charges are transferred to the deep inside the earth through the medium of low resistance lightening rod .

1d) Water molecules are polar in nature i.e. they have a charge separation due to the hydrogen bonding. So whenever a steam of water passes nearby a charged object , it always bend towards that charged object because the opposite charges between water molecule and object would attract each other .

1e) the 3 methods to charge an object are

(i) conduction - in this method a charged object is placed in physical contact with an unchanged object and hence the charges distribute among the two objects such that there is no net potential difference between the two objects .

(ii) friction- in this method two intially uncharged objects are rubbed against each other which results in the transfer of electrons from a body to other , hence the two bodies are equally and oppositely charged

(iii) induction- in this method, an uncharged object is placed in the vicinity of a charged object . The uncharged body will have its positively and negatively charged separated at the two ends due to the attraction by the opposite charge present in nearby charged body . Now the one end of the uncharged body is earthed and hence it is left with only charges which are held due to attractive force of nearby charged body . Therefore the uncharged body becomes oppositely charged