Chapter 21, Problem 79A

Interpretation Introduction

Interpretation: The plot showing characteristics of a dry cell needs to be identified.

Concept Introduction: A dry cell is an electrochemical cell consisting of low moisture immobilized electrolytes in the form of a paste, which restricts it from flowing. Due to this, it is easily transportable. An electrochemical cell containing low moisture electrolyte (in the form of a paste) is known as a dry cell. Therefore, a paste electrolyte is used in a dry cell in which there is only enough moisture to allow the flow of current.

Explanation of Solution

Reason for the correct option:

In a dry cell, due to an increase in the current through internal resistance, voltage exponentially decreases with time. The inverse relationship between voltage and time is shown in graph (b); thus, the correct option is (b).

Conclusion

Reason for incorrect options:

In graph (a), the voltage decreases with time. Thus, it is an incorrect option.

Similarly in graph (c), initially voltage is constant with time and then there is a sharp decrease at one point. Thus, it is an incorrect option.

Now in graph (d), there is a linear relationship between voltage and time showed which is not correct thus, it is also an incorrect option.