ISCET DC Circuit Analysis 4 — Questions and Answers
Question 1: Thevenin's theorem replaces a complex two-terminal network with:
- A voltage source in series with a resistance (Correct answer)
- A current source in parallel with a resistance
- Two voltage sources in parallel
- A single resistor
Correct answer: A voltage source in series with a resistance
The Thevenin equivalent is Vth (open-circuit voltage) in series with Rth (equivalent resistance).
Question 2: To find the Thevenin resistance of a circuit containing only independent sources, you should:
- Deactivate all sources and measure resistance at the terminals (Correct answer)
- Measure voltage at the terminals
- Short circuit the terminals and measure current
- Double the load resistance
Correct answer: Deactivate all sources and measure resistance at the terminals
Rth is found by deactivating all independent sources and calculating the resistance seen from the open terminals.
Question 3: What is the maximum power transfer condition in a DC circuit?
- Load resistance equals source resistance (Correct answer)
- Load resistance is twice the source resistance
- Load resistance is zero
- Load resistance is infinite
Correct answer: Load resistance equals source resistance
Maximum power is transferred when RL = Rs (or RL = Rth), per the maximum power transfer theorem.
Question 4: A 50Ω load is connected to a Thevenin equivalent circuit of 100V and 50Ω. What power is delivered to the load?
- 50W (Correct answer)
- 100W
- 200W
- 25W
Correct answer: 50W
I = 100/(50+50) = 1A; P = I²×RL = 1²×50 = 50W.
Question 5: In the Norton equivalent circuit, the Norton current is equal to:
- The short-circuit current at the terminals (Correct answer)
- The open-circuit voltage divided by load resistance
- The Thevenin voltage divided by load resistance
- The current through the internal resistance
Correct answer: The short-circuit current at the terminals
Norton current (IN) is measured by placing a short circuit across the output terminals and measuring the resulting current.
Question 6: How is the Norton equivalent resistance (RN) related to the Thevenin equivalent resistance (Rth)?
- RN = Rth (Correct answer)
- RN = 1/Rth
- RN = Vth/IN
- RN = 2×Rth
Correct answer: RN = Rth
RN equals Rth because both are calculated the same way: deactivate sources and find resistance at terminals.
Question 7: A circuit uses mesh analysis. In a mesh containing a 10V source and two resistors of 4Ω and 6Ω carrying mesh current I, what equation represents KVL?
- 10 = 4I + 6I (Correct answer)
- 10 = 4I − 6I
- 10 = (4+6)/I
- 10 = I/(4+6)
Correct answer: 10 = 4I + 6I
KVL around the mesh sums the voltage source against all resistive drops: 10 = 4I + 6I = 10I, giving I = 1A.
ISCET DC Circuit Analysis 4
Thevenin's theorem replaces a complex two-terminal network with: