Which of the following is less likely to be considered a simple resistive load in automotive circuits?

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Multiple Choice

Which of the following is less likely to be considered a simple resistive load in automotive circuits?

In automotive circuits, a simple resistive load follows Ohm’s law with a nearly constant resistance, so current changes linearly with voltage and there’s little phase shift between voltage and current. A starter motor isn’t like that. It’s a DC motor with windings (an inductive element) and, as it spins, it generates back-EMF that acts like a small generator opposing the applied voltage. This back-EMF causes the current to depend on speed and position, not just a fixed resistance, so the current draw changes nonlinearly during cranking. There’s also a very high inrush or stall current when the motor is not yet turning, which further shows it’s not a simple resistive load. Light bulbs and headlight filaments behave as resistors for practical purposes—their resistance is determined by temperature and they largely follow Ohm’s law within operating conditions. Radios and other electronics contain active circuitry, but they don’t exhibit the same inductive back-EMF behavior as a motor, so they’re closer to simple resistive behavior than a starter motor.

In automotive circuits, a simple resistive load follows Ohm’s law with a nearly constant resistance, so current changes linearly with voltage and there’s little phase shift between voltage and current. A starter motor isn’t like that. It’s a DC motor with windings (an inductive element) and, as it spins, it generates back-EMF that acts like a small generator opposing the applied voltage. This back-EMF causes the current to depend on speed and position, not just a fixed resistance, so the current draw changes nonlinearly during cranking. There’s also a very high inrush or stall current when the motor is not yet turning, which further shows it’s not a simple resistive load.

Light bulbs and headlight filaments behave as resistors for practical purposes—their resistance is determined by temperature and they largely follow Ohm’s law within operating conditions. Radios and other electronics contain active circuitry, but they don’t exhibit the same inductive back-EMF behavior as a motor, so they’re closer to simple resistive behavior than a starter motor.

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