# Chapter Notes: Current Electricity (Class 12 Physics)

Current Electricity Class 12 Classnotes with Numericals and PDF | Download Physics Notes |

## Current Electricity Class 12 Classnotes with Numericals and PDF | Download Physics Notes

## 1. Introduction to Current Electricity:

**Current (I):** The flow of electric charge in a conductor is termed as current. It is measured in Amperes (A).

**Conventional Current vs Electron Flow: **Conventional current assumes that positive charges flow, while in reality, electrons (negatively charged) move. However, for simplicity, conventional current is considered in circuit analysis.

## 2. Electric Current and Drift Velocity:

** Drift Velocity `(v_d)`:** It is the average velocity of charged particles (electrons in a conductor) in response to an electric field.

**Relation between Current and Drift Velocity:** `(I = nAe v_d)`, where I is the current, n is the charge carrier density, A is the cross-sectional area, e is the charge of an electron.

## 3. Ohm's Law:

** Ohm's Law Equation:**(V = IR), where V is voltage, I is current, and R is resistance.

** Ohmic and Non-Ohmic Conductors:** Materials following Ohm's law are ohmic conductors; others are non-ohmic.

## 4. Electrical Resistance:

** Resistance (R):** Opposition to the flow of electric current. Measured in Ohms `\(\Omega\)`.

** Factors Affecting Resistance:** Length (l), Cross-sectional Area (A), Temperature (T), and Material.

## 5. Resistivity (ρ) and Temperature Dependence:

**Resistivity (ρ):** Intrinsic property of a material to oppose the flow of current.

** Temperature Dependence:** Resistivity increases with temperature for most conductors.

## 6. Combination of Resistors:

**Series Combination:**` \(R_{\text{total}} = R_1 + R_2 + R_3 + \ldots\)`

** Parallel Combination:`** \(\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots\)`

## 7. EMF and Internal Resistance:

** Electromotive Force (EMF):** Voltage supplied by a source like a battery.

**Internal Resistance (r):** Resistance within the source.

**Terminal Voltage:** `\(V = \text{EMF} - Ir\)`

## 8. Kirchhoff’s Laws:

** Kirchhoff’s Current Law (KCL):** At any junction in a circuit, the total current entering equals the total current leaving.

**Kirchhoff’s Voltage Law (KVL):** The algebraic sum of the potential differences in any closed loop of a network is zero.

## 9. Electric Power and Heating Effect:

**Power (P):** Rate of doing work. `\(P = VI = I^2R = \frac{V^2}{R}\)`

**Heating Effect:** Electric power can produce heat in resistors. `\(H = VIt = I^2Rt = \frac{V^2t}{R}\)`

## 10. Numerical Problems:

1. Calculate the current flowing through a resistor of 10 ohms when a voltage of 5 volts is applied.

2. Determine the resistance of a wire with a length of 2 meters and a cross-sectional area of 0.5 cm², given the resistivity as `\(2 \times 10^{-7} \, \Omega \cdot \text{m}\).`

3. Find the total resistance of resistors in series: `\(R_1 = 3 \, \Omega\), \(R_2 = 5 \, \Omega\), and \(R_3 = 2 \, \Omega\).`

4. Calculate the power dissipated in a resistor of 8 ohms when a current of 4 amperes flows through it.

These chapter notes provide a comprehensive overview of the key concepts in Current Electricity, including definitions, equations, and numerical problems for practice.

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