Concept Notes
Network theorems are powerful tools to simplify and analyze electrical circuits.
1. Ohm’s Law (Basic Law)
2. Superposition Theorem
- In a linear circuit with multiple sources, the total response is the algebraic sum of responses due to each source acting alone (while other sources are replaced).
- Replace:
- Voltage source → short circuit
- Current source → open circuit
3. Thevenin’s Theorem
- Any linear circuit can be replaced by:
- Thevenin Voltage (
) = open-circuit voltage - Thevenin Resistance (
) = equivalent resistance seen at the terminals with all independent sources replaced
- Thevenin Voltage (
Equivalent Circuit: Voltage source in series with resistance .
Load Current:
4. Norton’s Theorem
- Any linear circuit can be replaced by:
- Norton Current (
) = short-circuit current - Norton Resistance (
) = same as
- Norton Current (
Equivalent Circuit: Current source in parallel with .
Relation with Thevenin:
5. Maximum Power Transfer Theorem
- Maximum power is delivered to the load when:
Maximum Power:
6. Reciprocity Theorem
- In a linear, bilateral circuit: If a voltage source
applied at branch A produces current 
in branch B, then the same voltage applied at branch B produces the same current at branch A.
7. Millman’s Theorem
- For parallel branches with sources:
8. Tellegen’s Theorem
- In any network:
⚙️ Formulas
Thevenin Load Current:
Norton Equivalent:
Maximum Power:
Millman’s Voltage:
🧮 Solved Example
Q: A circuit has 
and 
. If load 
, find maximum power.
Solution:
🔟 10 MCQs
Q1. Thevenin equivalent resistance is calculated by:
a) Open circuiting all sources
b) Short circuiting all sources
c) Replacing voltage sources by short and current sources by open
d) None
Q2. Norton current is:
a) Open circuit voltage
b) Short circuit current
c) Maximum load current
d) None
Q3. For maximum power transfer, 
must be:
a) Zero
b) Infinity
c) Equal to
d) Greater than
Q4. Maximum power transfer condition is valid only for:
a) Linear networks
b) Non-linear networks
c) Both
d) None
Q5. The relation between Thevenin and Norton is:
a) 
b) 
c) 
d) None
Q6. Reciprocity theorem is applicable to:
a) Linear networks
b) Non-linear networks
c) Time-varying networks
d) All
Q7. In Millman’s theorem, equivalent voltage is given by:
a) Sum of all voltages
b) Weighted average of branch voltages
c) Product of voltages
d) None
Q8. If 
, 
, maximum power is:
a) 20 W
b) 10 W
c) 5 W
d) 100 W
Q9. Tellegen’s theorem is based on:
a) KCL & KVL
b) Ohm’s law
c) Superposition
d) None
Q10. A Norton equivalent circuit consists of:
a) Voltage source in series with resistance
b) Current source in parallel with resistance
c) Voltage source in parallel with resistance
d) None
✅ Answer Key
| Q No | Answer |
|---|---|
| Q1 | c |
| Q2 | b |
| Q3 | c |
| Q4 | a |
| Q5 | a |
| Q6 | a |
| Q7 | b |
| Q8 | a |
| Q9 | a |
| Q10 | b |
🧠 Explanations
- Q1: Thevenin’s R → replace sources (V=short, I=open).
- Q2: Norton current = short-circuit current.
- Q3: Maximum power transfer → .
- Q4: Valid only for linear, bilateral networks.
- Q5: Conversion relation.
- Q6: Reciprocity valid only for linear networks.
- Q7: Millman’s = weighted average.
- Q8:
. - Q9: Tellegen’s theorem based on KCL & KVL.
- Q10: Norton’s equivalent = current source || resistance.
🎯 Motivation
- Network Theorems = Shortcut Tool → Instead of solving entire circuit with KVL/KCL, you can reduce it to simple forms.
- ECET always asks 2–3 questions from Thevenin, Norton, and Maximum Power Transfer.
- Mastering these saves time in exam and avoids silly mistakes.
👉 Remember: “Theorems are like cheat codes for circuits – learn them well, save marks fast!”
📲 CTA
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