निम्नलिखित के मान ज्ञात कीजिए -
`int_(r^(1))^(r_(2))(kq_(1)q_(2))/(r^(2))dr.`

Options

A. `q_(1)q_(2)((k)/(r_(1))-(1)/(r_(2)))`
B. `kq_(1)q_(2)((1)/(r_(1))-(1)/(r_(2)))`
C. `kq_(1)q_(2)((1)/(r_(1))+(1)/(r_(2)))`
D. `q_(1)q_(2)((1)/(r_(1))-(k)/(r_(2)))`

Answer

B

Explanation

`I=int_(r_(1))^(r_(2))(kq_(1)q_(2))/(r^(2))dr=kq_(1)q_(2)int_(r_(1))^(r_(2))(dr)/(r_(1))=kq_(1)q_(2)[(r^(-2+1))/(-2+1)]`
`=-kq_(1)q_(2)[(1)/(r)]_(r_(1))^(r_(2))=kq_(1)q_(2)((1)/(r_(1))-(1)/(r_(2))).`