Question 1

Multiple choiceMedium1 mark

Two fixed point charges, +Q+Q and −Q-Q are separated by 2a2a where Q>0Q>0 Point PP is midway between them. Let kk be Coulomb’s constant. Which row gives the electric potential at PP and the location chosen as the zero of electric potential?

Electric potential at PPZero-potential reference
A.00infinity
B.2kQa\dfrac{2kQ}{a}infinity
C.00PP
D.kQa\dfrac{kQ}{a}infinity
Show answer and explanation

Answer: A. For a point charge, V=kq/rV=kq/r when the potential is zero at infinity. At PP the contributions are +kQ/a+kQ/a and −kQ/a-kQ/a so their scalar sum is V(P)=0V(P)=0 The reference location for zero potential is infinity.

B: adds the magnitudes of the two contributions, ignoring the negative charge’s sign.
C: confuses a point where the net potential is zero with the location chosen as the zero reference.
D: includes the contribution from +Q+Q but omits the equal contribution from −Q-Q

Remember: electric potentials add as signed scalars.

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