  Question

# Two point charges and are located apart in vacuum (a) What is the electric field at the midpoint O of the line joining the two charges?(b) If a negative test charge of magnitude is placed at this point, what is the force experienced by the test charge?

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## (a) The situation is represented in the given figure. O is the mid-point of line AB. Distance between the two charges, Net electric field at point Electric field at point O caused by +3 C charge, along OBWhere,  Permittivity of free spaceMagnitude of electric field at point O caused by - 3 C charge, along OB [As = , the value is multiplied with 2] N/ C   along OB Therefore, the electric field at mid-point O is  N/ C  along OB.(b) A test charge of amount  is placed at mid-point O.Force experienced by the test charge The force is along line OA. This is because the negative test charge is repelled by the charge placed at point B but attracted towards point A.Hence, the force experienced by the test charge is along OA.

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