Two point charges +1 nC and 4 nC are 1 m apart in air. Find the positions along the line joining the two charges at which resultant potential is zero.

Explanation

At A charge is `1 xx 10^(-9) C`
At B charge is `- 4 xx 10^(-9) C `
Now at P resultant potential is zero.
` therefore (1)/(4 r epsi_0) [ (1 xx 10^(-9))/(x ) - (4 xx 10^(-9))/(1 - x) ] = 0`
`([(1 xx x) - 4(x)] xx 10^(-9))/(x(1 -x )) = 0`
` + 1 - x -4x = 0`
` 1 = 5x`
`x= 1/5 = 0.2m`