Automotive Electronics Practice Test

A series circuit has two 10 ohm bulbs and a third 10 ohm bulb is added. Which technician is correct about the brightness of the bulbs?

1. Technician A only

2. Technician B only

3. Both Technicians A and B

4. Neither Technician A nor B

The correct answer is: Technician A only

In a series circuit, the total resistance increases with the addition of more components. When the third 10 ohm bulb is added to the existing two 10 ohm bulbs, the total resistance of the circuit becomes 30 ohms (10 + 10 + 10). The brightness of the bulbs in a series circuit is determined by the current flowing through them. As the total resistance increases, the overall current flowing in the circuit decreases, assuming the voltage source remains constant. With less current flowing through each bulb due to the higher total resistance, each bulb will emit less light, resulting in reduced brightness. If Technician A states that the brightness of the bulbs will decrease with the addition of the third bulb, that statement aligns with the fundamental principles of series circuits. In this scenario, Technician A correctly articulates the impact of increasing resistance on current and, consequently, on brightness. This understanding of series circuits underscores why the assertion made by Technician A is accurate.