### Notes from Toppers

**Equivalent Circuits**

1. Basic Circuit Theory:

**Concepts of Equivalent Circuits:**

An equivalent circuit is a simplified representation of a complex circuit, reduced to an equivalent ideal circuit with a single voltage source, internal resistance, and circuit elements.

**(Reference: NCERT Physics Class 12 - Chapter 1 - Electric Charges and Fields)**

Concepts of Simple Series and Parallel Circuits:

- Understand the distinction between series arrangement (components connected in a single path) and parallel arrangement (same voltage across multiple paths) in circuits.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

Kirchhoff’s Laws Application:

- Employ Kirchhoff’s Current Law (KCL) andKirchhoff’s Voltage Law (KVL) to analyze and solve problems related to current and potential differences in complex circuits.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

2. Thévenin’s Theorem:

**Thévenin’s Equivalent Circuit:**

Comprehend the concept of Thévenin’s equivalent circuit, where an entire circuit is replaced by a single voltage source in series with an internal resistance.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

**Thévenin Voltage and Resistance Identification:**

Analyze a circuit to determine both Thévenin’s voltage (open-circuit voltage) and Thévenin’s resistance (resistance seen from source terminals with no load connected).

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

**Circuit Simplification:**

Simplify complex circuits by replacing portions of the circuit with equivalent Thévenin circuits, reducing the effort in circuit analysis.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

3. Norton’s Theorem:

Norton’s Equivalent Circuit:Understand Norton’s equivalent, similar to Thévenin’s but with a current source in parallel with an internal resistance.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

**Norton Current and Resistance:**

Determine Norton’s current (short circuit current) and Norton’s resistance.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

**Thévenin-Norton Conversion:**

Convert between Thévenin and Norton equivalent circuits as required for problem-solving.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

4. Superposition Theorem:

Superposition Approach:

Apply superposition to calculate circuit’s response by superimposing the effects of individual sources, where only one source is active at a time.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

5. Maximum Power Transfer Theorem:

Maximum Power Condition:

Identify and design circuits for maximum power transfer from a source to a load by matching impedances.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

6. Star-Delta Transformations:

Conversion Between Star-Delta Networks:

Understand star-delta transformations to convert between equivalent star and delta networks, simplifying analysis and calculations.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**

7. Millman’s Theorem:

Millman’s Theorem Understanding:

Comprehend Millman’s theorem, which simplifies parallel circuits with multiple voltage sources, reducing them to a single voltage source in series with an equivalent resistance.

**(Reference: NCERT Physics Class 12 - Chapter 3 - Current Electricity)**