Initially, three point charges form a right triangle in the –plane. Charge is at the…

PHYSICS · Multi-part · CBSE · Physics · Electrostatic Potential and Capacitance · Electrostatic Potential and Capacitance

Problem

Initially, three point charges form a right triangle in the

xy

–plane. Charge

q_{1}=+2.0\,\mu\text{C}

is at the origin, charge

q_{2}=+2.0\,\mu\text{C}

is at

(0.30\,\text{m},0)

, and charge

q_{3}=-3.0\,\mu\text{C}

is at

(0,0.40\,\text{m})

. A two–step process then occurs: • Step 1: Charge

q_{3}

is removed to a location very far away. • Step 2: A new charge

q_{4}=+3.0\,\mu\text{C}

is brought in from infinity and placed at the point originally occupied by

q_{3}

. Throughout the procedure, the positions of

q_{1}

and

q_{2}

remain fixed. (a) Calculate the total electric potential energy of the original three–charge configuration. (b) Calculate the total electric potential energy of the final configuration containing

q_{1}

q_{2}

, and

q_{4}

. (c) Determine the net external work done during the entire two–step process. State clearly whether this work is done on the charges or by the charges. (d) Suppose instead that

q_{1}

were

-2.0\,\mu\text{C}

(negative) while all other charges remained the same. Without repeating detailed calculations, predict qualitatively whether the magnitude of the external work in part (c) would increase, decrease, or stay the same. Justify your answer based on pairwise interactions.

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