Two point charges -q and +q are located at points (0,0, -a) and (0,0,a) respectivley. What is the electric potential at point (0,0, z)? (z > a)
A
qa4πϵ0z2
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B
q4πϵ0a
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C
2qa4πϵ0(z2−a2)
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D
2qa4πϵ0(z2+a2)
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Solution
The correct option is C2qa4πϵ0(z2−a2) Refer to Fig. 20.29. The distance of point P1 from charge + q is r1=z−a and from charge -q is r2=z+a ∴ Potential at P1=14πϵ0(qr1−qr2) =q4πϵ0.r2−r1r1r2=2qa4πϵ0(z2−a2)
Which is choice (c).