Nonohmic Materials: A Definition and Examples
Definition:
Nonohmic materials are materials that do not follow Ohm's Law, which states that the current flowing through a conductor is directly proportional to the voltage applied across its ends. In other words, the resistance of nonohmic materials is not constant and changes with the applied voltage or current.
Examples:
Here are some common examples of nonohmic materials:
1. Diodes:
* Semiconductors: Diodes are made of semiconductor materials like silicon or germanium.
* Unidirectional Current: Diodes allow current to flow easily in one direction (forward bias) but offer high resistance in the opposite direction (reverse bias).
* Application: Diodes are essential components in rectifiers, which convert alternating current (AC) to direct current (DC).
2. Thermistors:
* Temperature-dependent Resistance: Thermistors are resistors whose resistance changes significantly with temperature.
* Two Types:
* NTC (Negative Temperature Coefficient): Resistance decreases as temperature increases.
* PTC (Positive Temperature Coefficient): Resistance increases as temperature increases.
* Applications: Thermistors are used in temperature sensors, overcurrent protection devices, and other temperature-sensitive circuits.
3. Varistors:
* Voltage-dependent Resistance: Varistors are resistors whose resistance decreases significantly with increasing voltage.
* Non-linear Behavior: Varistors exhibit a high resistance at low voltages but a low resistance at high voltages.
* Application: Varistors are used as surge protectors to protect electronic devices from voltage spikes.
4. Transistors:
* Current Amplification: Transistors are semiconductor devices that amplify or switch electronic signals.
* Non-ohmic Behavior: The current flowing through a transistor is not directly proportional to the voltage applied.
* Applications: Transistors are essential components in amplifiers, oscillators, and other electronic circuits.
5. Gas Discharge Tubes:
* Plasma-based Conductance: Gas discharge tubes rely on the ionization of gas to conduct electricity.
* Breakdown Voltage: These tubes exhibit a high resistance until a certain voltage is reached, after which the resistance drops significantly.
* Applications: Gas discharge tubes are used in fluorescent lamps, neon signs, and some types of high-voltage switches.
Other Examples:
* Light-dependent resistors (LDRs): Resistance changes with light intensity.
* Memristors: Resistance changes with the history of the applied current.
Note:
The behavior of nonohmic materials can be complex and depends on several factors, including temperature, voltage, and the specific material composition. Understanding their non-linear characteristics is crucial for designing and analyzing electronic circuits that utilize them.