Charges are placed on the vertices of a square as shown. Let E be the electric field and V the potential at the centre. If the charges on A and B are interchanged with those on D and C respectively, then
(A)E remains unchanged, V changes
(B)both E and V change
(C)E and V remain unchanged
(D)E changes, V remains unchanged✓ Correct
Answer: (D)
Solution
This item depends on a figure that is not reproduced in the bank: charges of stated sign sit on the four corners of a square, and the question asks what happens to the field and the potential at the centre when the corner charges are swapped between the two diagonally related pairs. Without the diagram the exact placement of the signs cannot be fixed, so the item cannot be worked reliably as it stands. On the arrangement used in this paper the swap reverses the direction of the field contributions, so the vector field E at the centre changes, while the scalar potential V, which depends only on the magnitudes of the charges and their equal distances to the centre, is unchanged. The figure should be restored before the question is used.
JEE Main · 2007 · 29 Apr 2007 · Offline · Single correct option
