AP Physics 1 Exam Question:

A circuit consists of a power source, a resistor, and an ammeter connected in series. The power source provides an electric potential difference of 12 volts. The ammeter reads a current of 3 amperes. Determine the resistance of the resistor.

(a) 36 ohms (b) 4 ohms (c) 9 ohms (d) 15 ohms

Answer and Explanation:

To determine the resistance of the resistor, we can use Ohm's Law, which states that the voltage across a resistor is equal to the current through it multiplied by its resistance:

where:

• $V$ is the voltage across the resistor (in volts)
• $I$ is the current through the resistor (in amperes)
• $R$ is the resistance of the resistor (in ohms)

In this case, we are given the voltage ($V = 12$ volts) and the current ($I = 3$ amperes), and we need to solve for the resistance ($R$). Rearranging the equation, we get:

Substituting the given values, we have:

Simplifying the expression, we find:

Therefore, the resistance of the resistor is 4 ohms. Hence, the correct answer is (b) 4 ohms.