Q 1.1) What is the force between two small charged spheres having charges of 2 × 10–7C and 3 × 10–7 C placed 30 cm apart in the air?
Q 1.2) The electrostatic force on a small sphere of charge is 0.4 µC due to another small sphere of charge –0.8 µC in the air is 0.2 N.
(a) What is the distance between the two spheres?
(b) What is the force on the second sphere due to the first?
Soln:
(a) Given,
(b) Since the spheres have opposite charges, the force on the second sphere due to the first sphere will also be equal to 0.2N.
(b) Since the spheres have opposite charges, the force on the second sphere due to the first sphere will also be equal to 0.2N.Q 1.3) Check that the ratio ke2/G memp is dimensionless. Look up a Table of Physical Constants and determine the value of this ratio. What does the ratio signify?
Soln.:
The ratio to be determined is given as follows :
Q 1.4) (i) Explain the meaning of the statement ‘electric charge of a body is quantised’.
(ii) Why can one ignore the quantisation of electric charge when dealing with macroscopic, i.e. large-scale charges?
Soln.:
(i) The ‘electric charge of a body is quantized’ means that only integral (1, 2, …n) numbers of electrons can be transferred from one body to another.
Charges cannot get transferred in fractions. Hence, the total charge possessed by a body is only in integral multiples of electric charge.
(ii) In the case of large-scale or macroscopic charges, the charge which is used over there is comparatively too huge to the magnitude of the electric charge. Hence, on a macroscopic level, the quantisation of charge is of no use. Therefore, it is ignored, and the electric charge is considered to be continuous.
Q 1.5) When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.
Soln.:
When two bodies are rubbed against each other, a charge is developed on both bodies. These charges are equal but opposite in nature. And this phenomenon of inducing a charge is known as charging by friction. The net charge on both of the bodies is 0, and the reason behind it is that an equal amount of charge repels it. When we rub a glass rod with a silk cloth, a charge with the opposite magnitude is generated over there. This phenomenon is in consistence with the law of conservation of energy. A similar phenomenon is observed with many other pairs of bodies.
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