Question

Mention the limitations of Ohm’s law.

Answer 1

Hint: According to the Ohm’s law the electrical resistance of a conductor to the passage of current is equal to the potential difference , V divided by the electric current I i.e. Electric current = Voltage / Resistance.

Complete Step-by-Step solution:
Ohm’s law states that the electric current is proportional to the voltage and is inversely proportional to the resistance. But Ohm’s law is not applicable for all the materials . Hence, the limitations of Ohm’s law are:
1. Ohm’s law is not applicable for unilateral electrical elements like diodes and transistors as they allow the current to flow through in one direction only.
2. For non- linear electrical elements with parameters like capacitance, resistance etc the voltage and current won’t be constant with respect to time making it difficult to use Ohm’s law.
Examples of Limitations of Ohm’s Law:
1. Diode is an example which helps in understanding the limitations of Ohm’s law . When the voltage versus current graph is plotted for a diode it is observed that the relation between voltage and current is not linear. This happens when the voltage is marked in the reverse direction such that the magnitude is fixed. It is seen that the current is produced in the opposite direction with a different magnitude.
2. Consider a water volt-ammeter. IT is an example of a unilateral network and Ohm’s law is not applicable for such networks.
3. Also, it is not necessary that all conductors obey Ohm’s law . There are semi- conductors such as Silicon and Germanium which don’t obey Ohm’s law and they are known as Non-Ohmic conductors.

Note: The limitations will be : V ceases to be proportional to I. The relation between V and I depends on the sign of V. In other words, if I is the current for a certain V, then reversing the direction of V keeping its magnitude fixed, does not produce a current of the same magnitude as I in the opposite direction. This happens for example in case of a diode. The relation between V and I is not unique i.e. there is more than one value of V for the same current I . A material exhibiting such behavior is GaAs.