A point charge `q_(1)=+6e` fixed at the origin of a coordinate system, and another point charge `q_(2)=-10e` is fixed at `x=8nm`, `y=0` the locus of all points in the xy plane for which potential `V=0` (other man inifinity) is a circle centered on the x-axis as shown.
Q. The potential at the centre of the circle is

Options

A. `0.77V`
B. `0.32V`
C. `1.2V`
D. `-1.2V`

Answer

A

Explanation

On the positive side of x axis, potential is zero at distance `x_(1)` (it is between bothh charges), then ,brgt `(k.6e)/(r)=(k.10e)/(8-r)impliesr=3nm`
for the left side
`(k.6e)/(x_(2))=(k.10e)/(8+x_(2))impliesx_(2)=12nm`
`R=(x_(1)+x_(2))/(2)=7.5nm`
`|X_(C)|=X_(2)-R=4.5nm`
`V_(C)=(k.6e)/(4.5xx10^(-9))-(k.10e)/(12.5xx10^(-9))`
`=9xx10^(9)xx10^(9)xx1.6xx10^(-19)[(4)/(3)-(4)/(5)]`
`=1.44x=0.77v`