Question

Ohm's law is not obeyed by:
A.Electrolytes
B.Discharge tube
C.Vacuum tube
D.All of the above

Answer 1

Hint: To answer this question, you should know what Ohm's law. Ohm's law shows the relation between current, voltage and resistance across a circuit. It states that current is proportional to the potential difference and inversely proportional to resistance. And the resistance of a particular conductor remains constant even if other factors are varied. So using these relations, find the components which obey Ohm's law and which components do not obey Ohm's law.

Complete answer:
Ohm's law is given by,
V= IR
Where, V is the potential difference the conductor
            R is the resistance across the conductor
            I is the current flowing through the conductor
Ohm’s law states that at a constant temperature, current flowing through a conductor is directly proportional to the potential difference applied across the conductor and inversely proportional to resistance.
From the above equation, it can be inferred that Ohm's law is obeyed by conductors which have constant resistance even when current, and voltage are varied. A metallic conductor with varying temperature does not obey Ohm’s law. These types of conductors are called Non-ohmic temperature.
Electrolytes and discharge tubes show linear variation as their resistivity does not change with temperature. Hence, they obey Ohm's law.
While a vacuum tube shows change in conductance with change in temperature, and thus, change in resistivity. Thus, a vacuum tube is a non-linear circuit.
Therefore, Ohm's law is not obeyed by vacuum tubes.

Hence, the correct answer is option C i.e. vacuum tube.

Note:
Voltage and current graphs for Ohmic conductors will be a straight line as they obey Ohm's law. If we consider non-ohmic conductors voltage and current graph will not be a straight line as they do not obey Ohm's law. Thus, we can differentiate between Ohmic and Non-ohmic conductors.