PSAT Math Multiple-Choice Question 560: Answer and Explanation

Question: 560

Electrical engineers use Ohm's law, V = IR, to give the relationship among voltage (V), current (I), and resistance (R). Which of the following statements is always true about the relationship among voltage, current, and resistance based on Ohm's law?

If the current increases and the resistance remains the same, the voltage increases.

If the voltage increases, the resistance must increase.

If the resistance increases and the voltage remains the same, the current must decrease.

• A. I only
• B. II only
• C. I and III only
• D. II and III only

Correct Answer: C

Explanation:

(C) Choice I is correct. Increasing current while keeping resistance constant increases the right side of the equation. This means the left side—the voltage—increases as well. Choice III is correct. If the voltage—the left side of the equation—remains the same while the resistance increases, the current must decrease in order for the value on the right side of the equation to remain the same. Choice II is NOT correct. The current could increase without the resistance increasing if the voltage increases.