A Level Physics Practice Exam

What is indicated by a non-ohmic component?

1. Constant resistance

2. Variable resistance

3. Zero resistance

4. Infinite resistance

The correct answer is: Variable resistance

A non-ohmic component is characterized by a variable resistance, meaning that its resistance changes with the applied voltage or current. This behavior deviates from Ohm's law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points. In a non-ohmic component, the relationship between voltage and current is not linear, so the resistance is not constant. For example, devices such as diodes and thermistors exhibit non-ohmic behavior. As the voltage across a diode increases, the current increases exponentially after a certain threshold, indicating that the resistance is changing. Similarly, in thermistors, resistance decreases with an increase in temperature. This understanding is crucial in analyzing circuits that include non-linear components and in predicting their behavior under different operating conditions. The other options, such as constant resistance, zero resistance, and infinite resistance, describe scenarios typical of ohmic components or specific ideal cases, and do not accurately represent the nature of a non-ohmic component's resistance variation.