Question

Consider a linear active two-terminal network connected across terminals Y and Z. If the Thevenin equivalent resistance (\(R_{TH}\)) of this network is calculated to be 0 \(\Omega\), the network behaves essentially as an:

• A. Ideal Current Source
• B. Ideal Voltage Source
• C. Practical Voltage Source
• D. Open Circuit

Hint:

Remember the ideal source characteristics by their internal resistances: \begin{itemize} \item Ideal Voltage Source: \(R_{series} = 0 \, \Omega\) \item Ideal Current Source: \(R_{parallel} = \infty \, \Omega\) \end{itemize} This direct mapping helps in quickly solving such conceptual problems.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify the nature of a two-terminal network based on its Thevenin equivalent resistance. The key information is that \(R_{TH} = 0 \, \Omega\).
Step 2: Detailed Explanation:
1. Thevenin's Theorem:
Thevenin's theorem states that any linear, two-terminal network can be replaced by an equivalent circuit consisting of a single voltage source, \(V_{TH}\), in series with a single resistor, \(R_{TH}\). The voltage \(V_{TH}\) is the open-circuit voltage at the terminals, and the resistance \(R_{TH}\) is the equivalent resistance seen from the terminals with all independent sources turned off (voltage sources shorted, current sources opened).
2. Analyzing the case \(R_{TH} = 0 \, \Omega\):
If we draw the Thevenin equivalent circuit with \(R_{TH} = 0 \, \Omega\), the series resistance becomes a short circuit (a wire with zero resistance). The equivalent circuit simplifies to just the Thevenin voltage source, \(V_{TH}\), connected to the terminals.
3. Definitions of Source Models:

• Ideal Voltage Source: An ideal voltage source is a theoretical circuit element that provides a constant voltage across its terminals, regardless of the current drawn from it. Its key characteristic is having zero internal series resistance.
• Practical Voltage Source: A practical voltage source is a more realistic model, represented by an ideal voltage source in series with a small internal resistance (\(R_{internal}>0\)).
• Ideal Current Source: An ideal current source provides a constant current, regardless of the voltage across its terminals. Its internal resistance (in the parallel Norton model) is infinite.
• Open Circuit: An open circuit is a break in the circuit, corresponding to infinite resistance.

Step 3: Final Answer:
A network with a Thevenin resistance of \(0 \, \Omega\) is equivalent to a voltage source \(V_{TH}\) with a series resistance of zero. This is the definition of an ideal voltage source. The network will maintain a constant voltage \(V_{TH}\) across its terminals Y and Z, irrespective of the load connected.