### Notes from Toppers

**Series and Parallel Combinations of Cells - Current and Electricity**

**Detailed Notes from Toppers**

**1. Electric Current and Potential Difference:**

**Reference:**NCERT Physics Class 12, Chapter 1: Electric Charges and Fields**Key Points:**- Electric current is the rate of flow of electric charges.
- Potential difference is the difference in electric potential between two points in a circuit.
- Ohm’s law states that the current flowing through a conductor is directly proportional to the potential difference across it.
- Factors affecting resistance: length, cross-sectional area, temperature, and material.

**2. Series Combination of Cells:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- In a series combination, cells are connected end-to-end, with the positive terminal of one cell connected to the negative terminal of the next.
- The total potential difference in a series circuit is equal to the sum of the potential differences across each cell.
- The equivalent resistance of a series circuit is equal to the sum of the resistances of each cell.
- Current flows through each cell in the same direction, but its value remains the same.

**3. Parallel Combination of Cells:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- In a parallel combination, cells are connected side-by-side, with the positive terminals of all cells connected together, and the negative terminals of all cells connected together.
- The total resistance of a parallel circuit is less than the resistance of any individual cell.
- Current divides and flows through each cell independently.
- The equivalent potential difference across each cell in a parallel circuit is the same.

**4. Internal Resistance of Cells:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- Internal resistance is the resistance offered by the internal components of a cell to the flow of current.
- Internal resistance can be calculated using experimental methods like voltmeter-ammeter method or potentiometer method.
- Internal resistance affects the terminal voltage of a cell, reducing its value from the EMF of the cell.
- Cells with lower internal resistance are generally more efficient.

**5. EMF and Terminal Voltage:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- Electromotive force (EMF) is the maximum potential difference a cell can produce when its terminals are open.
- Terminal voltage is the potential difference across the terminals of a cell when it is connected to a circuit.
- Terminal voltage is always less than EMF due to internal resistance.

**6. Kirchhoff’s Laws:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- Kirchhoff’s current law (KCL) states that the total current entering a junction must equal the total current leaving the junction.
- Kirchhoff’s voltage law (KVL) states that the sum of the potential differences around any closed loop in a circuit must always be zero.
- KCL and KVL are powerful tools for analyzing complex circuits.

**7. Cell Grouping and Voltage Multiplication:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- Cells can be grouped in series to increase the total EMF, and in parallel to decrease the total internal resistance.
- The total EMF of a series group is the sum of the EMFs of each cell, while the total internal resistance is also increased.
- The total EMF of a parallel group is the same as the EMF of each cell, while the total internal resistance is decreased.
- Cell grouping is done in practical applications like batteries and power supplies.

**8. Applications of Series and Parallel Combinations:**

**Reference:**NCERT Physics Class 12, Chapter 6: Current Electricity**Key Points:**- Series and parallel combinations of cells are used in various real-world applications.
- Series combinations are commonly found in flashlights, string lights, and voltage multipliers.
- Parallel combinations are used in household wiring, car headlights, and power distribution systems.

**Note:** Toppers suggest supplementing these detailed notes with practice questions, numerical problems, and additional reference material to deepen your understanding of the concepts and prepare effectively for JEE exams.