Consider two point charges separated by a fixed distance

PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

R

. One charge has a known value

q_{1}

, while the other charge

q_{2}

is unknown. The electric potential energy

U

of the system is measured experimentally. Answer the following theoretical questions. (a) Starting from the general expression for electric potential energy of a two-charge system, algebraically isolate

q_{2}

in terms of

U

q_{1}

, and

R

. (b) Discuss how the sign of

U

determines the possible algebraic sign of

q_{2}

if the sign of

q_{1}

is already known. Include all logical cases in your explanation. (c) Explain, without performing any calculation, how doubling the separation

R

would alter the numerical value of

q_{2}

required to maintain the same measured potential energy

U

. Support your answer with proportional reasoning.

Related theory

Electrostatic Potential Energy
Electric Potential
Potential energy of a system of charges
Electrostatic Potential and Capacitance

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