Concept Notes
1. Ohm’s Law
Ohm’s Law states that the current flowing through a conductor between two points is directly proportional to the potential difference across the two points, provided the temperature and physical conditions remain constant.
Mathematical form:
Where:
→ Voltage (Volts)
→ Current (Amperes)
→ Resistance (Ohms)
Example:
If a resistor of 
is connected across a 
supply:
2. Kirchhoff’s Laws
(a) Kirchhoff’s Current Law (KCL)
The algebraic sum of currents entering a node (junction) is zero.
Example:
At a node: 
(b) Kirchhoff’s Voltage Law (KVL)
The algebraic sum of all voltages around a closed loop is zero.
Example:
In a loop with a battery of 
and two resistors 
and 
:
3. Network Theorems
(a) Superposition Theorem
In a linear network with multiple sources, the current/voltage across any element is equal to the algebraic sum of currents/voltages caused by each source acting independently, while replacing other sources with their internal impedances.
Steps:
- Keep one source active, replace others:
- Voltage source → Short circuit
- Current source → Open circuit
- Find response.
- Repeat for all sources and sum responses.
(b) Thevenin’s Theorem
Any linear network can be replaced by an equivalent circuit consisting of:
- A single voltage source
(Thevenin voltage) in series with - An equivalent resistance
.
Steps:
- Remove load resistance.
- Find = Open-circuit voltage.
- Find = Equivalent resistance seen from load terminals.
- Final circuit:
.
Load current:
(c) Norton’s Theorem
Dual of Thevenin: Any network can be reduced to a current source 
in parallel with a resistance 
.
(d) Maximum Power Transfer Theorem
A load receives maximum power from a network when:
Maximum power:
⚙️ Formulas
- Ohm’s Law:
- KCL:
- KVL:
- Thevenin Load Current:
- Norton Current:
- Maximum Power:
🔟 10 MCQs
Q1. A 10Ω resistor has 5A flowing through it. Find the voltage across it.
a) 2V
b) 25V
c) 50V
d) 5V
Q2. At a node, three currents meet: 2A entering, 3A leaving, and entering. Find .
a) 1A
b) 5A
c) –1A
d) 2A
Q3. In a circuit, 10V source is applied across a 2Ω resistor. Find current.
a) 2A
b) 5A
c) 10A
d) 20A
Q4. KVL is based on which principle?
a) Energy conservation
b) Charge conservation
c) Power balance
d) None
Q5. Superposition theorem is applicable to:
a) Linear networks only
b) Non-linear networks
c) Both
d) None
Q6. Thevenin equivalent resistance is found by:
a) Removing load, open circuiting sources
b) Removing load, replacing sources with internal resistances
c) Removing load, keeping all sources active
d) None
Q7. In Norton’s theorem, is equal to:
a)
b)
c)
d) None
Q8. A network has 
. For 
, find maximum power delivered.
a) 5W
b) 10W
c) 20W
d) 100W
Q9. In a resistive network, KCL fails when:
a) Capacitance exists
b) Inductance exists
c) Charges accumulate at node
d) None
Q10. Maximum power transfer occurs when:
a) 
b)
c) 
d) 
✅ Answer Key
| Q.No | Answer |
|---|---|
| 1 | c |
| 2 | a |
| 3 | b |
| 4 | a |
| 5 | a |
| 6 | b |
| 7 | b |
| 8 | b |
| 9 | c |
| 10 | b |
🧠 Explanations
- Q1:
→ (c). - Q2: KCL →
→ 
→ (a). - Q3:
→ (b). - Q4: KVL is based on energy conservation → (a).
- Q5: Only valid for linear networks → (a).
- Q6: Sources replaced by internal resistance → (b).
- Q7: By definition,
→ (b). - Q8:
→ (b). - Q9: If charges accumulate → KCL fails → (c).
- Q10: Maximum power transfer → → (b).
🎯 Motivation / Why Practice Matters
Ohm’s Law, KVL/KCL, and Network Theorems are the foundation of all electrical circuits. Without mastering them, solving DC machines, AC circuits, or Power System problems becomes impossible. In ECET 2026, at least 15–20% of EEE questions directly depend on these basics. Practicing daily ensures speed and accuracy in problem-solving.
📲 CTA
👉 Join our dedicated ECET 2026 WhatsApp Group for daily practice, notes & quizzes:
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