Illustrate the law of conservation of charge using the example of $\beta^-$ decay, in which a neutron changes into a proton, an electron and an antineutrino, showing that the total charge before and after the decay is unchanged.

Illustrate the law of conservation of charge using the example of β^- decay, in which a neutron changes into a

Exercise · Q10

\beta^-

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✓ Free question

In $\beta^-$ decay, a neutron $n$ (charge $0$ ) converts into a proton $p$ , an electron $e^-$ , and an antineutrino $\bar\nu$ :

n \longrightarrow p + e^- + \bar\nu

Charge before the decay: the neutron carries charge $q_n=0$ .

Charge after the decay: the proton carries $q_p=+e$ , the electron carries $q_{e^-}=-e$ , and the antineutrino carries $q_{\bar\nu}=0$ ; their algebraic sum is

q_p+q_{e^-}+q_{\bar\nu} = (+e)+(-e)+0 = 0

The total charge is exactly $0$ both before and after the decay -- charge is conserved even though the number and identity of the particles present has completely changed, and even in a process (a fundamental particle transformation) that has nothing to do with rubbing or contact.

✓Final answer

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

CBSE 2026Set ANNUAL1 markMCQ
$Q. When a glass rod is rubbed with a silk cloth the charge acquired by glass rod is$
(a) Positive
(b) Negative
(c) Both positive and negative
(d) None of these
›Reveal solutionSolution

Charging by friction just moves electrons from one material to the other - it never creates charge.

When two different insulating materials are rubbed together, electrons are transferred from the material that holds them less tightly to the one that holds them more tightly. This is a property of the two materials (their position in the triboelectric series), not something created by the rubbing itself - the TOTAL charge of the glass+silk system stays zero (conservation of charge).

For glass rubbed with silk, silk has a stronger pull on electrons than glass does. So electrons move FROM the glass TO the silk. The glass rod, having lost electrons, is left with an excess of protons - a net positive charge. The silk cloth, having gained those electrons, becomes negatively charged by an exactly equal amount.

✓Final answer
$(a) Positive - glass loses electrons to silk on rubbing, leaving the glass rod positively charged.$
CBSE 2022Set ANNUAL1 mark
$Q. A ............ charged particle produced an electric field only around it. (Fill up the blank.) OR Above Curie temperature, a ferromagnetic material is found to behave as a paramagnetic substance. Point out right or wrong.$
›Reveal solutionSolution

A charge at rest produces only a static electric field; a moving charge additionally produces a magnetic field.

A charge produces an electric field around it regardless of its state of motion. However, a magnetic field is produced only by a moving charge (i.e., by a current). So a charged particle that is stationary (at rest) produces an electric field only, with no accompanying magnetic field, since there is no current associated with it.

✓Final answer
$A stationary charged particle produces an electric field only around it.$
CBSE 2020Set ANNUAL1 markMCQ
$Q. A positively charged body has$
(a) excess of electrons
(b) deficit of electrons
(c) excess of protons
(d) deficit of protons
›Reveal solutionSolution
A body's charge changes only through the gain or loss of electrons, never protons, so a positive charge always means a deficit of electrons.

Protons are locked inside the nucleus and cannot be added to or removed from a body by ordinary charging processes (friction, conduction, induction). Only the loose outer electrons can transfer between bodies.

If a body LOSES electrons, its protons now outnumber its electrons, so it carries a net POSITIVE charge - this is a deficit of electrons, not an excess of protons (the proton number is unchanged).

If a body GAINS electrons, it carries a net NEGATIVE charge.

So the correct description of a positively charged body is that it has a deficit of electrons.

✓Final answer
$(b) Deficit of electrons.$

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Q.Illustrate the law of conservation of charge using the example of $\beta^-$ decay, in which a neutron changes into a proton, an electron and an antineutrino, showing that the total charge before and after the decay is unchanged.

Concept understanding — Electric Charge and Its Properties

Q.Illustrate the law of conservation of charge using the example of β−\beta^-β− decay, in which a neutron changes into a proton, an electron and an antineutrino, showing that the total charge before and after the decay is unchanged.

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Q.Illustrate the law of conservation of charge using the example of $\beta^-$ decay, in which a neutron changes into a proton, an electron and an antineutrino, showing that the total charge before and after the decay is unchanged.

Unlock everything free for 14 days