Key Fact
Conservation of charge
Electric charge is neither created nor destroyed in any isolated system; total charge is conserved. Charge is quantised in integer multiples of e = 1.6 × 10⁻¹⁹ C.
-- NCERT Class 12 Physics, Ch. 1, p. 4Electric Charges Conservation
8 MCQs9-step worked example
Source: NCERT ElectrostaticsPYQ coverage: NEET 2024Official key: NTA-verifiedLast updated: 21 Sep 2026
Electric Charges Conservation, explained for NEET
The trap: reading "charge is conserved" as "charged particles can never be created or destroyed." NCERT Class 12 Physics Part I, Chapter 1 (Section 1.4.2, pages 4–5) says something narrower: the net charge of an isolated system cannot be created or destroyed, although the charge-carrying particles may be. When a neutron turns into a proton and an electron, two charged particles appear, but their charges are equal and opposite, so the total is zero before and after.
Charging is transfer, not creation. Rubbing a glass rod with silk moves some electrons from the rod to the silk: the rod becomes positive, the silk negative, and no new charge is created (NCERT Chapter 1, page 3). A body is charged positively by losing electrons and negatively by gaining them.
Three properties (NCERT Section 1.4, pages 4–5):
- Additivity — total charge is the algebraic sum, q₁ + q₂ + … + qₙ. Charge is a scalar, but unlike mass it can be negative, so signs matter.
- Conservation — within an isolated system, charges may be redistributed, but the total stays the same.
- Quantisation — every free charge is q = ne, where n is an integer (positive or negative) and e = 1.602192 × 10⁻¹⁹ C is the charge on a proton (+e) or electron (−e).
Conductors and insulators (NCERT Section 1.3, page 3). Conductors (metals, human and animal bodies, earth) have electrons that are comparatively free to move; charge given to a conductor spreads over its entire surface. Insulators (glass, porcelain, plastic, nylon, wood) keep charge at the place where it was put. That is why a plastic comb charges on rubbing but a metal spoon held in the hand does not — its charge leaks through the body to the ground.
Bridge to NEET. Questions ask for n = q/e (electrons added or removed?), whether a charge is an integer multiple of e, or the charge left after bodies share charge.
Watch out: at the macroscopic level (a charge of 1 μC is about 10¹³ e) quantisation has no practical consequence and charge looks continuous (NCERT page 6). It still holds.
Can you answer these Electric Charges Conservation MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
According to NCERT, the charge q on any body is given by q = ne. Here n is:
Show answer and why every option is right or wrong
Answer: B. NCERT Class 12 Physics Part I, Chapter 1, Section 1.4.3 (page 5): all free charges are integral multiples of e, q = ne, where n is any integer, positive or negative.
Why A is wrong: A is wrong because a negatively charged body (one that has gained electrons) needs a negative n; NCERT allows n to be positive or negative.
Why C is wrong: C is wrong because charge only looks continuous at the macroscopic scale; it can change only in steps of e, so n must be a whole number.
Why D is wrong: D is wrong because it confuses conservation with quantisation: equal and opposite charges appear together when charged particles are created, but a single body can carry an odd number of units of e.
MCQ 2Easy RecallPractice
In nature a neutron can turn into a proton and an electron. Which statement about charge in this process is correct?
Show answer and why every option is right or wrong
Answer: C. NCERT Class 12 Physics Part I, Chapter 1, Section 1.4.2 (pages 4–5): charge-carrying particles may be created, but the net charge of an isolated system cannot change; the proton (+e) and electron (−e) give a total of zero, the same as the neutron.
Why A is wrong: A is wrong because it forgets the electron's −e; adding +e and −e gives zero, not +e.
Why B is wrong: B is wrong because conservation applies to the net charge, not to the number of charged particles; NCERT states the particles may be created or destroyed in a process.
Why D is wrong: D is wrong because by convention the charge on an electron is −e; only the proton carries +e.
MCQ 3Easy RecallPractice
Which statement about conductors and insulators matches NCERT Class 12 Physics, Chapter 1?
Show answer and why every option is right or wrong
Answer: C. NCERT Class 12 Physics Part I, Chapter 1, Section 1.3 (page 3): charge transferred to a conductor readily gets distributed over its entire surface; charge put on an insulator stays at the same place.
Why A is wrong: A is wrong because it swaps the two behaviours; spreading over the surface is the conductor's property, staying in place is the insulator's.
Why B is wrong: B is wrong because NCERT lists human and animal bodies (and earth) as conductors; that is exactly why charge on a held metal article leaks to the ground.
Why D is wrong: D is wrong because NCERT (pages 3–4) says the comb gets electrified but a metal spoon does not, since its charge leaks through the body to the ground.
MCQ 4Direct ApplicationPractice
An isolated system contains four small charged bodies with charges +3 μC, −5 μC, +7 μC and −2 μC. The total charge of the system is:
Show answer and why every option is right or wrong
Answer: D. Charges add algebraically (NCERT Chapter 1, Section 1.4.1, page 4): (+3) + (−5) + (+7) + (−2) = +3 μC.
Why A is wrong: A is wrong because 17 = 3 + 5 + 7 + 2 adds the magnitudes and ignores the signs; charge can be negative, so signs must be kept.
Why B is wrong: B is wrong because −7 = (−5) + (−2) counts only the negative charges and leaves out +3 and +7.
Why C is wrong: C is wrong because +10 = (+3) + (+7) counts only the positive charges and leaves out −5 and −2.
MCQ 5Direct ApplicationPractice
A neutral metal sphere acquires a charge of +4.8 × 10⁻⁹ C. Taking e = 1.6 × 10⁻¹⁹ C, how many electrons were transferred, and in which direction?
Show answer and why every option is right or wrong
Answer: A. n = q/e = (4.8 × 10⁻⁹)/(1.6 × 10⁻¹⁹) = 3.0 × 10¹⁰. The charge is positive, so the sphere lost electrons (NCERT Chapter 1, pages 3 and 5).
Why B is wrong: B is wrong because 3.3 × 10⁻¹¹ comes from e/q = 1.6 × 10⁻¹⁹ / 4.8 × 10⁻⁹, the inverted ratio.
Why C is wrong: C is wrong because the count is right but the direction is reversed; gaining electrons would make the sphere negative, not positive.
Why D is wrong: D is wrong because 7.7 × 10⁻²⁸ comes from multiplying q × e = 4.8 × 10⁻⁹ × 1.6 × 10⁻¹⁹ instead of dividing q by e; a number of electrons cannot be a tiny fraction.
MCQ 6Direct ApplicationPractice
Taking e = 1.6 × 10⁻¹⁹ C, which of these values CANNOT be the charge on an isolated body?
Show answer and why every option is right or wrong
Answer: D. q/e = (2.4 × 10⁻¹⁹)/(1.6 × 10⁻¹⁹) = 1.5, which is not an integer, so this charge violates q = ne (NCERT Chapter 1, Section 1.4.3, page 5).
Why A is wrong: A is wrong because 3.2 × 10⁻¹⁹ / 1.6 × 10⁻¹⁹ = 2, an integer, so this charge is allowed (n = 2).
Why B is wrong: B is wrong because 4.8 × 10⁻¹⁹ / 1.6 × 10⁻¹⁹ = 3, an integer, so this charge is allowed (n = 3).
Why C is wrong: C is wrong because 8.0 × 10⁻¹⁹ / 1.6 × 10⁻¹⁹ = 5, an integer, so this charge is allowed (n = 5).
MCQ 7CalculationPractice
Two identical metal spheres carry charges +12 μC and −4 μC. They are touched together and then separated. By symmetry the charge is shared equally. The charge on each sphere afterwards is:
Show answer and why every option is right or wrong
Answer: A. Total charge is conserved (NCERT Chapter 1, Section 1.4.2, page 4): (+12) + (−4) = +8 μC. On contact the charge spreads over the two identical conductors (Section 1.3, page 3) and splits equally: +8/2 = +4 μC each. Check: 4 + 4 = 8 μC, the same total as before.
Why B is wrong: B is wrong because it halves each original charge (12/2 and −4/2) instead of first adding them; the spheres would still carry opposite charges after touching, which cannot be the final equal share.
Why C is wrong: C is wrong because it gives the whole +8 μC total to each sphere; the combined charge would become +16 μC, which breaks conservation.
Why D is wrong: D is wrong because it assumes no charge moves on contact; charge on a conductor readily spreads over its whole surface, so the two metal spheres share it.
MCQ 8CalculationPractice
A glass rod rubbed with silk acquires a charge of +8.0 × 10⁻¹⁰ C. Taking e = 1.6 × 10⁻¹⁹ C, which statement is correct?
Show answer and why every option is right or wrong
Answer: B. No charge is created in rubbing, so what the rod gains the silk loses: silk = −8.0 × 10⁻¹⁰ C. n = (8.0 × 10⁻¹⁰)/(1.6 × 10⁻¹⁹) = 5.0 × 10⁹ electrons, moving from the rod to the silk, which leaves the rod positive (NCERT Chapter 1, pages 3–4).
Why A is wrong: A is wrong because both bodies would then be positive and the total would be +1.6 × 10⁻⁹ C from a neutral start; conservation requires the silk to be negative.
Why C is wrong: C is wrong because electrons arriving at the rod would make it negative; the rod is positive, so electrons left it.
Why D is wrong: D is wrong because NCERT states no new charge is created in rubbing; the rod's charge comes from losing electrons to the silk.
Free NEET study resources
Get a structured 30-day Mechanics plan and a complete formula booklet — delivered to your inbox instantly.
How do you solve a Electric Charges Conservation question? A worked example
- 1
Given
10⁹ electrons move out of a body to another body every second. Charge on an electron: magnitude e = 1.6 × 10⁻¹⁹ C.
- 2
Required
The time needed for the other body to collect a total charge of 1 C (magnitude).
- 3
Concept
Quantisation: charge moves in whole units of e, so the charge transferred per second is (number of electrons per second) × e. Charge accumulates steadily, so time = total charge ÷ charge per second.
- 4
Formula
q = ne; charge per second = (10⁹ s⁻¹) × e; t = Q ÷ (charge per second).
- 5
Substitution
Charge per second = 1.6 × 10⁻¹⁹ C × 10⁹ = 1.6 × 10⁻¹⁰ C/s
t = 1 C ÷ (1.6 × 10⁻¹⁰ C/s) - 6
Calculation
t = 6.25 × 10⁹ s
In years: 6.25 × 10⁹ ÷ (365 × 24 × 3600) = 198 years
The factors 365, 24 and 3600 are exact conversion counts and the 10⁹ electrons per second is a count set by the problem; they do not limit the significant figures. NCERT keeps 198 years and then rounds it to "approximately 200 years". - 7
Final answer
About 6.25 × 10⁹ s, which is 198 years (roughly 200 years). One coulomb is a very large unit for many practical purposes.
- 8
Common trap
Multiplying 1 C by the charge per second (giving 1.6 × 10⁻¹⁰, a meaningless "time"), or dividing by the number of electrons alone (1/10⁹ = 10⁻⁹ s) and forgetting that each electron carries only 1.6 × 10⁻¹⁹ C. Check the units: C ÷ (C/s) gives seconds.
- 9
Similar NEET-style question
"If 2.0 × 10¹⁰ electrons are transferred from one body to another every second, how long does it take for the charge on the receiving body to reach a magnitude of 3.2 × 10⁻⁶ C? (e = 1.6 × 10⁻¹⁹ C)"
Strategy: charge per second = 2.0 × 10¹⁰ × 1.6 × 10⁻¹⁹ = 3.2 × 10⁻⁹ C/s; t = 3.2 × 10⁻⁶ ÷ 3.2 × 10⁻⁹ = 1.0 × 10³ s. The receiving body gains electrons, so its charge is negative.
---
What to remember before solving Electric Charges Conservation questions
More in Electrostatics: 3 exam traps and mistakes · 11 formulas · 6 question patterns from its other lessons.
Electric Charges Conservation questions from past NEET papers
1 question from NEET 2024. Answers verified against NTA official keys. — click to collapse
NEET 2024Revised key
1Both Statement I and Statement II are correct
2Both Statement I and Statement II are incorrect
3Statement I is correct but Statement II is incorrect
4Statement I is incorrect but Statement II is correct
NTA Answer: Option 3(revised_final)
Sources
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
Test yourself on this topic with real past-paper questions:
Practice this topic →Prefer to watch this?
7 real NEET Electrostatics questions (2022–2025), from field lines to capacitors, solved step by step (14 min)
Watch on YouTube