Question

Question 1.11: A polythene piece rubbed with wool is found to have a negative charge of 3 × 10 −7 C. (a) Estimate the number of electrons transferred (from which to which?) (b) Is there a transfer of mass from wool to polythene?

Class 12 - Physics - Electric Charges And Fields Electric Charges And Fields Page-46

Answer 1

(a) We know, electric charge of a body is quantized
e.g., Q = ne
Given, Q = 3 × 10⁻⁷C
e = 1.6 × 10⁻¹⁹ C [ charge on each electron ]
n = Q/e = 3 × 10⁻⁷/1.6 × 10⁻¹⁹
= 3/1.6 × 1.875 × 10¹²
So, 1.875 × 10¹² electrons have transferred from wool to polythene .

(b) yes , as you know, mass of electron = 9.1 × 10⁻³¹ kg
∴ transfer of mass = number of electron × mass of each electron
= 1.875 × 10¹² × 9.1 × 10⁻³¹
= 1.71 × 10⁻¹⁸ Kg has transferred from whool to polythene.

Answer 2

(a) We know, electric charge of a body is quantized

e.g., Q = ne

Given, Q = 3 × 10⁻⁷C

e = 1.6 × 10⁻¹⁹ C [ charge on each electron ]

n = Q/e = 3 × 10⁻⁷/1.6 × 10⁻¹⁹

= 3/1.6 × 1.875 × 10¹²

So, 1.875 × 10¹² electrons have transferred from wool to polythene .

(b) yes , as you know, mass of electron = 9.1 × 10⁻³¹ kg

∴ transfer of mass = number of electron × mass of each electron

= 1.875 × 10¹² × 9.1 × 10⁻³¹

= 1.71 × 10⁻¹⁸ Kg has transferred from whool to polythene.