Question

Consider the following statements.
1. Ohm’s law is not applicable at very low temperatures and very high temperatures.
2. Ohm’s law is applicable for semiconductors.
3. Ohm’s law is not applicable to electron tubes, discharge tubes and electrolytes.
4. Conductance is reciprocal of resistance and is measured in Siemens.
Which of the statements given are correct?
A.\[1{\text{ , 2 and 3}}\]
B. \[1{\text{ , 2 and 4}}\]
C. \[1{\text{ , 3 and 4}}\]
D. \[1{\text{ , 2, 3 and 4}}\]

Answer 1

Hint: We are given statements which are related to the ohm law of electric current. We will examine each property of Ohm's law and then we will observe which statement is correct and which is not a correct statement. We will also study the conductance of the conductor.

Complete answer:
According to Ohms’ Law, the electric current \[I\] flowing through a conductor is directly proportional to the potential difference \[V\] applied across both ends of the conductor, providing that the physical conditions like temperature and pressure remain unchanged. This can be represented as,
\[I{\text{ }} \propto {\text{ V }}\] or \[{\text{V }} \propto {\text{ I }}\]
\[{\text{V = IR }}\], on removing the proportionality sign a new constant resistance comes.

Thus when we draw the linear relation between the potential difference and current we get the straight slope whose slope is resistance. This relationship only holds when temperature is neither too low nor too high. Thus we can say that Ohm’s law is not applicable at very low temperatures and very high temperatures. Also semiconductors only follow Ohm's law for a short duration of time but after sometime they do not follow.

Thus we can say that Ohm’s law is not applicable for semiconductors. In discharge tubes, electrons tube and electrolytic cells, the property of electrons changes which do not follow ohm’s law. The reciprocal of resistance is known as conductance and it is denoted by Siemens or mho. The relation can be represented as,
Conductance of the conductor\[ = {\text{ }}\dfrac{1}{{{\text{Resistance of conductor}}}}\]
Therefore we can say that the correct statement is \[1{\text{ , 3 and 4}}\].

Hence, the correct answer is option C.

Note: While describing the ohm’s law we must remember the conditions. Resistance is the barrier for electrons for flow of electric current whereas conductance helps electrons for flow of electric current. Since the unit of resistance is ohm, hence the unit of conductance is also mho.