Current-Voltage Characteristics of Elements p and q:

The current-voltage characteristics of elements p and q are shown in the given graphs. It is required to determine which graph represents the characteristics when p and q are in series.

Series Circuit:

When elements are connected in series, the same current flows through each element. The total voltage across the series combination of elements is equal to the sum of the individual voltages across each element.

Analysis:

To identify the correct graph representing the current-voltage characteristics when p and q are in series, we need to consider the following points:

1. Current: In a series circuit, the current is the same through all elements. Therefore, the graph representing the series combination should have a constant current value throughout.

2. Voltage: The total voltage across the series combination is equal to the sum of the individual voltages. So, the graph representing the series combination should have a voltage value that is the sum of the voltages across p and q at each corresponding current value.

Identifying the Correct Graph:

Based on the above analysis, we can identify the correct graph by comparing the given graphs with the expected characteristics of a series circuit.

The correct graph representing the current-voltage characteristics when p and q are in series is:

Graph 4:
- It shows a constant current value throughout, indicating that the current is the same in both p and q.
- The voltage values in the graph are obtained by adding the voltage values of p and q at each corresponding current value, which aligns with the series circuit characteristics.

Conclusion:

Graph 4 represents the current-voltage characteristics when elements p and q are connected in series. It satisfies the expected behavior of a series circuit, where the current remains constant and the voltage is the sum of the individual voltages across each element.