Question

Is Ohm’s law universally applicable for all conducting elements? If not, give examples of elements that do not obey Ohm’s law.

Answer 1

Hint: According to Ohm's law if the physical conditions of the conductor (length, temperature, etc...) remain the same, then the current flowing through the conductor is directly proportional to the potential difference across its ends. Consider the elements whose temperature increases with the increase in current.

Complete step-by-step solution:
Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it provided; the temperature and physical conditions must remain constant.
So according to this statement if a temperature of a substance increases then there is a violation of ohm's law and hence ohm’s law will not be applicable to that element. For example, in the case of the filament (tungsten) in the light bulb, as the current increases the temperature will also increase. Therefore in this situation the Ohms law cannot be applied. That is tungsten does not obey Ohm’s law.
Elements that follow the Ohm’s law are called ohmic elements and those that do not follow Ohm’s law are called non-ohmic elements. Some of the examples are semiconductor diodes, vacuum tubes, liquid electrolyte etc.

Note: Not all elements are ohmic elements, in fact there are many elements such as germanium, tungsten and devices such as LED that do not obey Ohm’s law. Hence Ohm’s law is not universally applicable to all conducting elements. For an ohmic element the graph between the voltage and current is a straight line that is the voltage is directly proportional to the current flowing through the ends of a conductor.