Electric Charge, Quantisation and Conservation

Identify whether electrons are gained or lost. Write q = ne. Substitute n and e with units. Decide the sign from electron gain or loss. State the physical meaning of the sign.

A simple diagram may show a neutral body, electron transfer, and final positive and negative bodies. Useful labels are electrons transferred, body losing electrons, body gaining electrons, and sign of charge.

Writing -3.2 x 10^-9 C for a body that loses electrons is wrong because loss of electrons leaves a positive charge.

Electric charge is a fundamental property of matter due to which bodies exert electric forces on one another. It exists in two types, positive and negative, and any observable charge is an integral multiple of the elementary charge: q = ne.

Electric charge is a fundamental property of matter due to which bodies exert electric forces on one another. It exists in two types, positive and negative, and any observable charge is an integral multiple of the elementary charge: q = ne. Key rules: q = ne, where q is charge in coulomb, n is an integer, and e = 1.6 x 10^-19 C. Total charge is conserved in an isolated system and charges add algebraically. Use negative sign for excess electrons and positive sign for electron deficiency. If a body has 5 x 10^12 extra electrons, its charge is q = -ne = -(5 x 10^12)(1.6 x 10^-19 C) = -8.0 x 10^-7 C. The negative sign shows excess electrons.

A body becomes charged when it has an excess or deficiency of electrons. The SI unit of charge is coulomb (C). Charge is additive, so the total charge of a system is the algebraic sum of individual charges. Charge is conserved, meaning total charge in an isolated system remains constant. Charge is quantised because it occurs as q = ne, where n is an integer and e = 1.6 x 10^-19 C. At macroscopic scale, the discrete nature is usually not noticed because e is very small. Key rules: q = ne, where q is charge in coulomb, n is an integer, and e = 1.6 x 10^-19 C. Total charge is conserved in an isolated system and charges add algebraically. Use negative sign for excess electrons and positive sign for electron deficiency. A metal sphere loses 2 x 10^10 electrons. Charge developed = ne = (2 x 10^10)(1.6 x 10^-19 C) = 3.2 x 10^-9 C. Since electrons are lost, the sphere becomes positively charged. Final answer: +3.2 x 10^-9 C. Usually asked as a short answer on quantisation or conservation, a numerical on number of electrons transferred, or an assertion-reason question about why charge is conserved during charging by friction. Writing -3.2 x 10^-9 C for a body that loses electrons is wrong because loss of electrons leaves a positive charge.