Point charges q,−q,2Q and Q are placed in order at the corners A,B,C,D of a square of side 2b. If the field at the midpoint CD is zero, then qQ is:
Four point charges qA=2μC, qB=−5μC, qC=2μC, and qD=−5μC are located at the corners of a square ABCD of side 10cm. What is the force on a charge of 1μC placed at the centre of the square?