Discuss the basic properties of electric charges.

III. Long Answer Questions · Q1

Q. Discuss the basic properties of electric charges.

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Step 1. Additivity. Electric charge, like mass, is a fundamental scalar property of matter carried by protons ( $+e$ ) and electrons ( $-e$ ); the net charge on any object is the plain algebraic (signed) sum of all the charge it contains.

Step 2. Conservation. Benjamin Franklin argued, from rubbing experiments (e.g. glass rod on silk), that charging by friction does not create charge, only transfers it from one object to another. This is generalised to a fundamental conservation law: the total electric charge of an isolated system, and of the universe as a whole, is constant -- charge can neither be created nor destroyed, only transferred or redistributed.

Step 3. Quantisation. Millikan's oil-drop experiment established that charge always occurs as an integer multiple of the elementary charge $e=1.6\times10^{-19}\ \text{C}$ : $q=ne$ , $n$ an integer. At the macroscopic level (charging typically transfers $\sim10^{10}$ electrons), this graininess is unnoticeable, but it is fundamental at the atomic scale.

✓Final answer

q=ne

Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set ANNUAL1 markMCQ
$Q. Case study: When a glass rod is rubbed with silk, the rod acquires one type of charge, and the silk acquires the other type of charge. This is true for any pair of objects that are rubbed with each other to be electrified. Now the electrified glass rod is brought in contact with silk cloth, which was rubbed; they no longer attract each other. They also do not repel or attract each other light pieces of paper and other such objects; thus, charges they acquire by rubbing get lost when they come in contact with each other. When you comb in dry hairs it gets charged due to?$
(a) Friction
(b) Conduction
(c) Induction
(d) Grounding
›Reveal solutionSolution

Combing dry hair charges both the comb and hair by friction (triboelectric charging).

When a comb is rubbed against dry hair, electrons transfer from one surface to the other due to rubbing (friction). This leaves the comb and hair with equal and opposite charges — this is charging by friction, the same mechanism behind static-electricity build-up in everyday materials.

✓Final answer
$The hair/comb gets charged due to friction (option a).$
CBSE 2026Set ANNUAL1 markMCQ
$Q. Case study: When a glass rod is rubbed with silk, the rod acquires one type of charge, and the silk acquires the other type of charge. This is true for any pair of objects that are rubbed with each other to be electrified. Now the electrified glass rod is brought in contact with silk cloth, which was rubbed; they no longer attract each other. They also do not repel or attract each other light pieces of paper and other such objects; thus, charges they acquire by rubbing get lost when they come in contact with each other. Which part of atom physically manipulated in this type of electrification?$
(a) Protons
(b) Electrons
(c) Nucleus
(d) Neutrons
›Reveal solutionSolution

Frictional charging always involves the transfer of loosely bound outer electrons, never protons or the nucleus.

During charging by friction, only the electrons, being light and loosely bound in the outermost shells of atoms, get transferred from one surface to the other. Protons remain fixed within the nucleus and are never transferred; the object losing electrons becomes positively charged and the one gaining electrons becomes negatively charged.

✓Final answer
$Electrons are the particles physically transferred (option b).$
CBSE 2026Set ANNUAL1 markMCQ
$Q. Case study: When a glass rod is rubbed with silk, the rod acquires one type of charge, and the silk acquires the other type of charge. This is true for any pair of objects that are rubbed with each other to be electrified. Now the electrified glass rod is brought in contact with silk cloth, which was rubbed; they no longer attract each other. They also do not repel or attract each other light pieces of paper and other such objects; thus, charges they acquire by rubbing get lost when they come in contact with each other. Positive and negative charge on neutral objects are:$
(a) Double
(b) Equal
(c) Half
(d) Four times
›Reveal solutionSolution

A neutral object has exactly as much positive charge (protons) as negative charge (electrons), so the net charge is zero.

Every atom is built from protons (positive) and electrons (negative). An object is electrically neutral precisely when the total positive charge equals the total negative charge, so they cancel to give zero net charge.

✓Final answer
$Positive and negative charge on a neutral object are equal (option b).$
CBSE 2026Set ANNUAL1 mark
$Q. Case study: When a glass rod is rubbed with silk, the rod acquires one type of charge, and the silk acquires the other type of charge. This is true for any pair of objects that are rubbed with each other to be electrified. Now the electrified glass rod is brought in contact with silk cloth, which was rubbed; they no longer attract each other. They also do not repel or attract each other light pieces of paper and other such objects; thus, charges they acquire by rubbing get lost when they come in contact with each other. 3 balls K, L & M have charged 1 C, 3 C and 4 C respectively. The ball K is first brought into contact with L and then M. Find the final charge on M. OR Why we observe electric shock on touching a metallic door handle after moving on the floor with carpet?$
›Reveal solutionSolution

When identical conducting spheres touch, charge redistributes equally between them; applying this twice (K–L, then K–M) gives 3 C on M.

Step 1 — K touches L: Charges $q_K = 1\,\text{C}$ , $q_L = 3\,\text{C}$ share equally (identical spheres):

$q_K = q_L = \dfrac{1+3}{2} = 2\,\text{C each}$

Step 2 — K (now 2 C) touches M (4 C):

$q_K = q_M = \dfrac{2+4}{2} = 3\,\text{C each}$

So after both contacts, M carries a final charge of $3\,\text{C}$ .

✓Final answer
$Final charge on ball M = 3 C.$
CBSE 2019Set ANNUAL1 mark
$Q. Process of sharing the charges with the earth is called as ____________ .$
›Reveal solutionSolution

Connecting a charged body to the earth so that charge flows until the body's potential equals the earth's (taken as zero) is called earthing.

The earth is an enormous conductor, so it behaves like an infinite reservoir of charge — adding or removing charge from it produces no measurable change in its own potential. When a charged conductor is joined to the earth by a conducting wire, charge flows between the conductor and the earth until the potential of the conductor becomes equal to that of the earth (taken as the reference, V = 0). This is how excess charge on a body is safely removed.

✓Final answer
$The process is called earthing (or grounding) .$

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Q.Discuss the basic properties of electric charges.

Concept understanding — Basic Properties and Conservation of Electric Charge

Q.Discuss the basic properties of electric charges.

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