Ohm's Law is given by the equation V = IR where V is voltage in watts, / is current in amperes, and R is resistance in Ohms. A lamp needs 0.5 amperes. Which equation can be used to determine the voltage for a given amount of resistance?

A. V = 2R
B. V = 0.5R
C. V = 0.5/R
D. V = R/0.5