Electric Charge and its Properties

Electric charge and its specific properties

⊛ Charge is the fundamental property associated with matter due to which it produces and experiences electric and magnetic effects.

⊛ There are two types of charge : positive and negative. This categorization has been made just to distinguish the nature of interaction.

⊛ SI unit of charge is coulomb (abbreviated as C).

⊛ Charge is a scalar quantity which means it can be added or subtracted algebraically.

⊛ Charge resides on matter i.e. mass. Alternatively, without mass the existence of charge is not possible though mass can exist without charge. Thus, presence of charge itself is a convincing proof of existence of mass. This also follows that in the process of charging, mass of the body changes.

⊛ Charge is transferable. If we put a charged body in contact with another body, then charge can be transferred to another body.

⊛ Total charge of an isolated system is always conserved i.e. charge can neither be created nor destroyed. This holds good in all types of reactions either chemical or nuclear.

⊛ Unlike mass, total charge of a body does not depend on its speed i.e. charge is invariant. On the other hand, mass of a body is dependent on its speed (Greater the speed, greater is the mass) according to Einstein’s relativity theory.

⊛ Like charges repel while unlike attract.

⊛ Accelerated charge radiates energy in the form of electromagnetic waves.
Electric charge, electrostatics for iit jee

⊛ Charge is quantized. The quantization of charge is the property by virtue of which all free charges are integral multiple of a basic unit of charge represented by e (where e = ± 1.6 × 10⁻¹⁹ C). This value is the minimum possible quantity of charge which can exist individually and hence is known as the quantum of charge.

Thus if net charge on a body is Q, it is expressible as Q = ±ne, where n = 1, 2, 3, 4...

And therefore charge on a body can never be ±√2e, ±πe, ±1.2e etc.

Some Illustrations

Q1. There are two identical metallic spheres. Now one is given +5C of charge and the other -5C of charge and thus their masses become m₁ and m₂ respectively. Choose the correct option from below: 
a) m₁ > m₂ 
b) m₁ < m₂ 
c) m₁ = m₂ 
d) Nothing can be said.
Hint : Option (b) is correct as from the positively charged sphere (+5C)/(+1.6 × 10⁻¹⁹C) number of electrons have been extracted while (-5C)/(-1.6 × 10⁻¹⁹C) number of electrons have been given to the other sphere.

Q2. If 10⁹ electrons are transferred from a body to another body per second, how much time is required to get a net charge of -1C on the other body (assuming it to be neutral initially)?

Hint : Time Required = (-1C)/(-1.6 × 10⁻¹⁹C × 10⁹ per second) = 6.25 × 10⁹ seconds = 198 years (approx.)
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