AQA GCSE HIGHER PHYSICS - Ohmic and Non-Ohmic Conductors

Ohmic and Non-Ohmic Conductors

Introduction

This tutorial will explore the behaviour of different types of conductors, specifically focusing on the distinction between ohmic and non-ohmic conductors. We'll learn how to identify them based on their current-voltage (I-V) characteristics and delve into the specific properties of components like thermistors and diodes.

Ohmic Conductors

• Definition: An ohmic conductor is a material that obeys Ohm's Law. This means that the current flowing through it is directly proportional to the voltage across it, provided the temperature remains constant.
• I-V Characteristic: The I-V graph of an ohmic conductor is a straight line passing through the origin.
• Resistance: The resistance of an ohmic conductor remains constant regardless of the applied voltage.

Example: A piece of wire made of a material like copper or nichrome is an example of an ohmic conductor at room temperature.

Non-Ohmic Conductors

• Definition: Non-ohmic conductors are materials that do not obey Ohm's Law. Their resistance changes depending on factors like temperature or the applied voltage.
• I-V Characteristic: The I-V graph of a non-ohmic conductor is not a straight line. Its shape can vary depending on the specific component.

Thermistors

• Definition: Thermistors are temperature-sensitive resistors. Their resistance decreases as the temperature increases (negative temperature coefficient) or increases as the temperature increases (positive temperature coefficient).
• I-V Characteristic: The I-V graph of a thermistor will show a non-linear relationship.
• Applications: Thermistors are used in various applications, including temperature sensors, temperature control systems, and over-current protection.

Diodes

• Definition: Diodes are semiconductor devices that allow current to flow in only one direction. They have a very high resistance in the reverse direction and a low resistance in the forward direction.
• I-V Characteristic: The I-V graph of a diode shows a sharp increase in current once the forward voltage exceeds the forward voltage drop.
• Applications: Diodes have numerous applications, including rectifiers, voltage regulators, and signal detectors.

Summary

Understanding the difference between ohmic and non-ohmic conductors is crucial for analyzing circuits and designing electronic systems. Each conductor type has unique characteristics that make them suitable for specific applications.