NEIEP Mechanics Practice Exam

What is the primary function of varistors?

1. Regulate voltage

2. Prevent component damage from surges

3. Convert AC to DC

4. Provide amplification

The correct answer is: Prevent component damage from surges

Varistors, also known as voltage-dependent resistors, primarily serve the function of preventing component damage from surges. They are designed to protect circuits by shunting excessive voltage away from sensitive components during voltage spikes. When the voltage across a varistor exceeds a certain threshold, its resistance decreases dramatically, allowing it to absorb and dissipate the excess energy. This rapid change in resistance helps to maintain a stable voltage environment in the circuit, thereby safeguarding against potential damage caused by transient events like power surges or lightning strikes. Other choices focus on different functions. For example, regulating voltage usually involves devices that maintain a steady voltage level, while converting AC to DC pertains to rectifiers, and providing amplification is a role typically associated with transistors and operational amplifiers. Varistors do not perform these roles; their unique property of altering resistance based on voltage levels is what defines their capability in surge protection.