JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech I Year BASIC ELECTRICAL ENGINEERING Previous Question Paper (July/August - 2021 - R18)

The superposition theorem is subject to the following limitations:

• It is applicable only to linear circuits, where the relationship between voltage and current is proportional. It cannot be used in circuits containing non-linear elements like diodes or transistors.
• It is not directly applicable to power calculations, as power is a non-linear function of current or voltage (P = I²R or P = V²/R). Power must be calculated only after finding the total current or voltage through the component.
• It is primarily useful for circuits with multiple independent sources. If a circuit has only one source, other methods like Ohm's law or nodal analysis are more efficient.
• It cannot be applied to circuits with dependent sources if those sources are controlled by variables that change when individual independent sources are turned off.

To find the current i using Thevenin's theorem, follow these steps:

1. Remove the load branch containing the current i and identify the open-circuit terminals A and B.
2. Calculate Thevenin voltage (V_th): This is the open-circuit voltage across terminals A and B. Use nodal or mesh analysis on the remaining circuit to find the potential difference between these terminals.
3. Calculate Thevenin resistance (R_th): Deactivate all independent sources (replace voltage sources with short circuits and current sources with open circuits) and calculate the equivalent resistance looking into terminals A and B.
4. Draw the Thevenin equivalent circuit: Connect the calculated V_th in series with R_th and the load resistance R_L that was previously removed.
5. Calculate the current: Use the formula
   i = V_th / (R_th + R_L)
   to determine the current flowing through the load branch.