Question

Two point charges `q_(A) = 3 mu C` and `q_(B) = -3 muC` are located 20 cm apart in vaccum (a) what is the electric field at the mid point O of the line AB joining the two charges ? (b) If a negative test charge of magnitude `1.5xx10^(-9) C` is placed at the point, what is the force experienced by the test charge ?

Answer 1

Here, `q_(A) = 3 mu C = 3xx10^(-6)C, q_(B) = -3 mu C = -3xx10^(-6) C`,
`AB = 20 cm`, Fig.
`r = OA = OB = 10cm = 10^(-1) m, E = ?`
Electric field is the force on unit positive charge `(+ 1C)` at O,
`E = (2 xx q_(A) xx1)/(4pi in_(0) r^(2)), E = (2xx3xx10^(-6)x9xx10^(9))/((10^(-1))^(2)) = 5.4xx10^(6) N//C` along OB
Force on negative charge `q = -1.5xx10^(-9)C` at O will be
`F = qE = -1.5xx10^(-9) (5.4xx10^(6)) N`
`F = -8.1xx10^(-3)N` , along BA