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Electrostatic Potential And Capacitance

Question
CBSEENPH12037302

A charge of 8 mC is located at the origin. Calculate the work done in taking a small charge of –2 x 10–9 C from a point P(0, 0, 3 cm) to a point Q(0, 4 cm, 0), via a point R (0, 6 cm, 9 cm).

Solution

Given,
Charge, q =8 mC=8 x 10–3 C is located at origin and the small charge q0 =–2 x 10–9 C is taken from point P (0,0,3 cm) to a point Q (0,4 cm,0) through point R (0,6 cm,9 cm) as shown in the figure below.
Initial separation between q0 and q is rp = 3 cm = 0.03 m
Final separation between q0 and q is rQ = 4 cm = 0.04 m


Work done in taking the charge q
0 from point P to Q does not dependent on the path followed and depends only upon rp and rQ i.e., initial and final positions.
                 W = 14πε0qq01rQ-1rp        W = 9 × 109 × 8 × 10-3 × (-2×10-9) × 10.04-10.03     = 1.2 J.

Note: Point R is irrelevant to the answer.

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