Two test charges are brought successively to a position some distance away from a negative charge −Q. First, test-charge q is placed at a distance R from −Q. Then it is removed and a test-charge −2q is placed at a distance 2R from −Q. The sign of q is unknown. Compared with the electric potential at the position of the test-charge in the first case, the electric potential at the position of the second test-charge is
[Figure: Two diagrams showing (a) charge q at distance R from −Q, (b) charge −2q at distance 2R from −Q]
(a) the same.
(b) twice as large.
(c) half as large.
(d) impossible to determine unless the sign of q is known.