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A positive point charge ( q = +9.5 x 10 -8 C) is surrounded by an equipotential

ID: 2133712 • Letter: A

Question

A positive point charge (q = +9.5 x 10-8 C) is surrounded by an equipotential surface A, which has a radius of rA = 2.0 m. A positive test charge (q0 = +4.9 x 10-11 C) moves from surface A to another equipotential surface B, which has a radius rB. The work done by the electric force as the test charge moves from surface A to surface B is WAB = -7.9 x 10-9J. Find rB.

The number of significant digits is set to 3; the tolerance is +/-1 in the 3rd significant digit

A positive point charge (q = +9.5 x 10-8 C) is surrounded by an equipotential surface A, which has a radius of rA = 2.0 m. A positive test charge (q0 = +4.9 x 10-11 C) moves from surface A to another equipotential surface B, which has a radius rB. The work done by the electric force as the test charge moves from surface A to surface B is WAB = -7.9 x 10-9J. Find rB.

Explanation / Answer

the first charge is q1 = +9.5 x 10^-8 C

the radius is rA = 2.0 m

the second charge is q2 = +4.9 x 10^-11 C

let the radius be rB

the work done is W = -7.9 x 10^-9 J

we know that

W = k x (q1q2/rB - rA)

where k = (1/4pi x e_o) = 9 x 10^9 Nm^2/C^2

solving the above equation for rB

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