Which one of the following is NOT a basic property of electric charge ?
- A.Charges can be added
- B.Charge is conserved
- C.Charge on a body is always an integral multiple of an electron or a proton charge
- D.Charges can be created and destroyed in an isolated system
Correct answer
Explanation
The correct answer is D, Charges can be created and destroyed in an isolated system. This goes against the conservation of charge: the total charge of an isolated system always stays the same.
Electric charge has three basic properties. It is additive, so the total charge of a body is the algebraic sum of the charges on it, with signs taken into account. It is conserved, so charge can only be transferred from one body to another; when a glass rod is rubbed with silk, electrons move from glass to silk and the two get equal and opposite charges, but no net charge is made. Even when a particle and antiparticle are created or annihilate, equal positive and negative charges appear or vanish together. And it is quantised: any charge is q = ne, where e is 1.6 × 10⁻¹⁹ coulomb and n is a whole number.
A is wrong as an answer because additivity is a basic property. B is wrong as an answer because conservation is a basic property. C is wrong as an answer because this is quantisation of charge, also a basic property.
Exam tip: Charge is additive, conserved and quantised (q = ne, e = 1.6 × 10⁻¹⁹ C).
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