What is the voltage across a 10-ohm resistor if a current of 2 amperes flows through it?
Why Ohm's Law in the form E = I x R gives voltage when you know current and resistance. Here 2 amperes through 10 ohms yields 2 x 10 = 20 volts. Whenever the question gives current and resistance and asks for voltage, multiply.
Watch out The 0.2 volt choice comes from dividing 2 by 10 instead of multiplying, and the 8 and 12 volt choices come from subtracting or adding the two numbers, none of which is Ohm's Law.
Voltage asked, multiply: E = I x R. 2 A x 10 ohms = 20 V.