Two points charges `20 mu C and 10muC` are separated by 1m in air. Find the work done to separate them two metre apart.

Explanation

Data supplied,
`r_(1)=1m" "r_(2)=2m " "q_(1)=20 xx 10^(-6)C" "q_(2)=10 xx 10^(-6)C`
For air, `epsi_(r)=1`
Potential energy `U_(1)=(1)/(4pi epsi_(0)). (q_(1)q_(2))/(r_(1)) and U_(2)-(1)/(4pi epsi_(0)) .(q_(1)q_(2))/(r_(2))`
Work done `W=U_(1)-U_(2) =(1)/(4pi epsi_(0)).q_(1)q_(2) [1/r_(1)-1/r_(2)]=(1)/(4pi epsi_(0)).q_(1)q_(2) ((r_(2)-r_(1))/(r_(1)r_(2)))`
`=9 xx 10^(9) xx 20 xx 10^(-6) xx 10 xx 10^(-6) xx ((2-1))/(1 xx 2) ="0.9 joules"`