ARRL Technician Practice Exam

If a circuit draws 4 amperes from a 12-volt source, what is the resistance?

1. 2 ohms

2. 3 ohms

3. 4 ohms

4. 5 ohms

The correct answer is: 3 ohms

To determine the resistance in a circuit, Ohm's Law can be applied. Ohm's Law states that voltage (V) equals the current (I) multiplied by the resistance (R). This relationship can be expressed with the formula: \[ R = \frac{V}{I} \] In the given problem, the voltage (V) is 12 volts and the current (I) is 4 amperes. Plugging these values into the formula gives: \[ R = \frac{12 \text{ volts}}{4 \text{ amperes}} \] Carrying out the division results in: \[ R = 3 \text{ ohms} \] This calculation indicates that the resistance in the circuit is 3 ohms. Understanding this formula is crucial for anyone working with electrical circuits, as it allows for the calculation of one variable when the other two are known.