Ohm’s Law
Ohm’s Law states that the current (II) flowing through a conductor is directly proportional to the voltage (VV) across it, provided the temperature and other physical conditions remain constant.
Mathematically, it is expressed as:
V=IR
where:
- V = Voltage (Volts, V)
- = Current (Amperes, A)
- = Resistance (Ohms, Ω\Omega)
Limitations of Ohm’s Law
Ohm’s Law is not universally applicable. Some of its limitations include:
-
Temperature Dependence
- Ohm’s Law holds only when the temperature remains constant.
- In many materials, resistance changes with temperature (e.g., metals increase resistance at higher temperatures).
-
Non-Linear Conductors
- Some materials (e.g., semiconductors, diodes, transistors) do not follow Ohm’s Law.
- Their V−I graphs are non-linear.
-
High Voltage or Strong Electric Fields
- In gases and vacuum tubes, Ohm’s Law does not hold under strong electric fields.
-
Superconductors
- Superconductors have zero resistance below a critical temperature, violating Ohm’s Law.
Ohmic vs. Non-Ohmic Conductors
| Aspect | Ohmic Conductors | Non-Ohmic Conductors |
|---|---|---|
| Definition | Materials that obey Ohm’s Law (V=IR). | Materials that do not obey Ohm’s Law (non-linear V−I relationship). |
| Graph | Linear V−I graph (straight line). | Non-linear V−I graph (curved or exponential). |
| Examples | Metals (copper, silver, iron), resistors. | Diodes, transistors, semiconductors, filament bulbs. |
| Resistance | Constant with applied voltage. | Varies with applied voltage or temperature. |
Conclusion
Ohm’s Law is fundamental in electrical circuits but does not apply to all materials. Conductors are classified as ohmic if they follow Ohm’s Law and non-ohmic if they do not.