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 ?

Explanation

(a)The direction of the electric field intensity due to both the charges at the centre of the line joining the two charges will be along the line from the positive charge towards the negative charge. The magnitude of electric field can be calculated as:
`E=9xx10^9 [(3xx10^(-9))/(0.1)^2 +(3xx10^(-9))/(0.1)^2]`
`rArr E=5.4xx10^6` N/C
(b)The force experienced by the negative test charge :
`F=qE=1.5xx10^(-9)xx5.4xx10^6=8.1xx10^(-3)` N
The direction of force will be opposite to the direction of the electric field because the charge is negative.