Q.(i) Explain the meaning of the statement 'electric charge of a body is quantised'. (1 1/2)

Showing the 12 most recent of 27 on this concept.

1. CBSE 2026Set V11 markMCQ
   Q.Which one of the following charge cannot exist on a body?

   (a) $2\,e$

   (b) $3\,e$

   (c) $3.5\,e$

   (d) $-4\,e$

   ›Reveal solutionSolution

   (c) $3.5\,e$ …

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2. CBSE 2026Set ANNUAL1 markMCQ
   Q.Number of electrons in one coulomb charge are -

   (i) $6.25\times10^{18}$

   (ii) $6.25\times10^{12}$

   (iii) $6.25\times10^{10}$

   (iv) $6.25\times10^{14}$

   ›Reveal solutionSolution

   1 C of charge contains $1/e$ electrons.

   The charge on one electron is $e=1.6\times10^{-19}$ C. The number of electrons whose total charge is 1 coulomb is $n=\dfrac{1}{e}=\dfrac{1}{1.6\times10^{-19}}=6.25\times10^{18}$.

   …

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3. CBSE 2026Set DS1 markMCQ
   Q.Number of electrons emitted from a piece of metal for giving $1 \times 10^{-7}$ coulomb charge will be:

   i) $10^{7}$

   ii) $1.6 \times 10^{19}$

   iii) $6.25 \times 10^{11}$

   iv) $9 \times 10^{12}$

   ›Reveal solutionSolution

   Charge is quantised, so $n = Q/e = 6.25\times10^{11}$ electrons.

   Concept. Charge exists only in whole multiples of the electronic charge $e = 1.6\times10^{-19}$ C (quantisation of charge). If a metal piece loses a charge $Q$, the number of electrons removed is $n = \dfrac{Q}{e}$.

   Calculation. …

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4. CBSE 2026Set ANNUAL1 markMCQ
   Q.An object has a negative charge of 1 coulomb. The number of excess electrons on it is

   (a) 6.25 x 10^-18

   (b) 1.6 x 10^19

   (c) 1.6 x 10^-19

   (d) 6.25 x 10^18

   ›Reveal solutionSolution

   Charge is quantised: any charge Q is made up of a whole number of electron charges e, so n = Q/e.

   A negative charge means the object has more electrons than protons. Each electron carries a charge of magnitude e = 1.6 x 10^-19 C. If the object carries a total (excess) charge of magnitude Q, the number of excess electrons is

   …

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5. CBSE 2025Set 55/4/11 markMCQ
   Q.A body acquires charge $8.0 \times 10^{-12}$ C. The mass of the body: (A) increases by $4.5 \times 10^{-7}$ kg (B) decreases by $1.0 \times 10^{-6}$ kg (C) decreases by $4.55 \times 10^{-23}$ kg (D) increases by $9.1 \times 10^{-23}$ kg

   ›Reveal solutionSolution

   When a body gains positive charge, it loses electrons; the mass change equals the number of electrons lost times the electron mass. For $8.0 \times 10^{-12}$ C, the body decreases by $4.55 \times 10^{-23}$ kg.

   Why charging changes mass

   Charging a body means adding or removing electrons. Since electrons have mass ($m_e = 9.1 \times 10^{-31}$ kg), any change in the number of electrons changes the body's total mass.

   The sign of the charge tells us what happened:

   • Positive charge: electrons were removed → mass decreases
   • Negative charge: electrons were added → mass increases

   The magnitude of charge tells us how many electrons moved, since each electron carries charge $e = 1.6 \times 10^{-19}$ C.

   Finding the mass change

   1. Determine the number of electrons involved

      The charge acquired is $Q = 8.0 \times 10^{-12}$ C (positive). The number of electrons that must have been removed is:

   $n = \frac{Q}{e} = \frac{8.0 \times 10^{-12}}{1.6 \times 10^{-19}}$

   $n = 5.0 \times 10^{7} \text{ electrons}$

   2. Calculate the total mass of these electrons

      Each electron has mass $m_e = 9.1 \times 10^{-31}$ kg, so the total mass lost is:

   $\Delta m = n \times m_e = 5.0 \times 10^{7} \times 9.1 \times 10^{-31}$

   $\Delta m = 45.5 \times 10^{-24} = 4.55 \times 10^{-23} \text{ kg}$

   3. Determine the direction of change …

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6. CBSE 2025Set JS1 mark
   Q.A conductor has positive charge of $2.4 \times 10^{-18}$ coulomb. Find how much electrons are in deficit/excess on the conductor.

   ›Reveal solutionSolution

   A positive charge of $2.4\times10^{-18}$ C corresponds to a shortage of $n=q/e=15$ electrons.

   Concept — quantisation of charge. Charge exists only in integer multiples of the electronic charge $e=1.6\times10^{-19}$ C: $q=ne$. A positive conductor has lost electrons, so it has a deficit of electrons.

   Solution. …

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7. CBSE 2025Set A1 mark
   Q.Fill in the blank with appropriate word: One coulomb charge has ______ electrons.

   ›Reveal solutionSolution

   One coulomb of charge corresponds to about 6.25 × 10¹⁸ electrons.

   Charge is quantised: total charge $q = ne$, where $n$ is the number of electrons (or elementary charges) and $e = 1.6\times10^{-19}$ C is the magnitude of charge on a single electron. For $q = 1$ C:

   …

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8. CBSE 2025Set A1 mark
   Q.Write answer in one sentence: Write mathematical form of quantisation of electric charge.

   ›Reveal solutionSolution

   Quantisation of charge is expressed mathematically as q = ne.

   Experiments (starting with Millikan's oil-drop experiment) show that electric charge is never continuous but always occurs in discrete, integral multiples of a smallest indivisible unit of charge, called the elementary charge $e = 1.6\times10^{-19}$ C (the magnitude of the charge on an electron or proton). This is expressed mathematically as:

   $q = ne$

   …

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9. CBSE 2025Set ANNUAL1 markMCQ
   Q.How many electrons will have a charge of one Coulomb?

   (a) 6.25 x 10^18

   (b) 6.25 x 10^19

   (c) 5.25 x 10^18

   (d) 5.25 x 10^19

   ›Reveal solutionSolution

   Charge is quantized in units of the electronic charge e = 1.6 x 10^-19 C, so the number of electrons needed to make up 1 C is n = Q/e.

   Any charge Q is an integer multiple of the elementary charge: Q = n e.

   Here Q = 1 C and e = 1.6 x 10^-19 C, so

   n = Q/e = 1 / (1.6 x 10^-19) = 6.25 x 10^18

   …

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10. CBSE 2024Set A1 markMCQ
    Q.Number of electrons present in 8 coulomb negative charge is (A) 5 × 10^19 (B) 2.5 × 10^19 (C) 12.8 × 10^19 (D) 1.6 × 10^19

    ›Reveal solutionSolution

    n = Q/e = 8 ÷ (1.6×10⁻¹⁹) = 5×10¹⁹ electrons.

    Charge is quantised: total charge $Q = n\,e$, where $e = 1.6\times10^{-19}$ C.

    …

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11. CBSE 2024Set ANNUAL1 markMCQ
    Q.The minimum amount of charge observed so far is

    (a) 1 C

    (b) 4.8 x 10^-13 C

    (c) 1.6 x 10^-19 C

    (d) 1.6 x 10^19 C

    ›Reveal solutionSolution

    Charge is quantised: every observable free charge is an integer multiple of the elementary charge e = 1.6 x 10^-19 C, the smallest charge ever measured on a free particle.

    Millikan's oil-drop experiment established that electric charge does not take arbitrary values but always occurs as an integral multiple of a smallest unit, the electronic charge

    $e = 1.6 \times 10^{-19}\ \text{C}$

    …

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12. CBSE 2024Set ANNUAL1 mark
    Q.What does $q_1 + q_2 = 0$ signify in electrostatics?

    ›Reveal solutionSolution

    $q_1+q_2=0$ means the two charges are equal in magnitude and opposite in sign, giving zero net charge for the pair — the defining condition of a system like an electric dipole.

    If $q_1+q_2=0$, then $q_2=-q_1$: the two charges have exactly equal magnitude but opposite polarity (one is $+q$, the other is $-q$). This does not mean there is no electric field around them — a pair of equal and opposite charges separated by some distance still produces a field (this is precisely the definition of an electric dipole, with dipole moment $p=q\times(\text{separation})$, and it is only the algebraic (net) charge of the pair that vanishes, not the field. It also means that if this pair is enclosed inside a Gaussian …

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