Two equal positive point charges +Q are fixed 6 cm apart on a straight line. At which one of the following positions along the same line will the resultant electric field be zero (excluding infinity)?
a) Exactly at the mid-point of the two charges
b) At a point on the line to the right of the right charge
c) At a point between the charges, 2 cm from the left charge
d) No finite point on the line – the fields can never cancel