# Chapter 3: Current Electricity

Chapter 3 Current Electricity Class 12 Notes PDF |

## Electric Current

- Electric current is the rate of flow of electric charge in a conductor.

- It is denoted by the symbol 'I' and its unit is ampere (A).

## Electric Current and Drift Velocity

- Electric current is related to the drift velocity of charge carriers in a conductor.

- The drift velocity is the average velocity of charged particles in a particular direction due to an applied electric field.

## Ohm's Law

- Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided the physical conditions such as temperature and material remain constant.

- Mathematically, Ohm's Law can be expressed as: V = IR

where V is the potential difference, I is the current, and R is the resistance of the conductor.

## Resistance

- Resistance is a property of a conductor that determines the amount of current flowing through it for a given potential difference.

- It is denoted by the symbol 'R' and its unit is ohm (Ω).

- The resistance of a conductor depends on its length, cross-sectional area, and the material it is made of.

- The resistance of a conductor can be calculated using the formula: R = ρ (L/A)

where R is the resistance, ρ (rho) is the resistivity of the material, L is the length of the conductor, and A is the cross-sectional area of the conductor.

## Resistivity

- Resistivity is a property of a material that quantifies its resistance to the flow of electric current.

- It is denoted by the symbol 'ρ' (rho) and its unit is ohm-meter (Ω.m).

- Resistivity depends on the nature of the material and its temperature.

## Conductance

- Conductance is the reciprocal of resistance and represents the ease with which current can flow through a conductor.

- It is denoted by the symbol 'G' and its unit is siemens (S).

- The relationship between conductance and resistance is given by: G = 1/R.

## Numerical Example 1:

A wire has a resistance of 5 Ω. If a potential difference of 10 V is applied across its ends, calculate the current flowing through the wire using Ohm's Law.

### Solution:

Given: R = 5 Ω, V = 10 V

Using Ohm's Law: V = IR

10 = I * 5

I = 10/5

I = 2 A

Therefore, the current flowing through the wire is 2 A.

## Numerical Example 2:

A wire of length 2 m and cross-sectional area 3 mm² has a resistivity of 1.6 × 10⁻⁸ Ω.m. Calculate its resistance.

### Solution:

Given: L = 2 m, A = 3 mm² = 3 × 10⁻⁶ m², ρ = 1.6 × 10⁻⁸ Ω.m

Using the formula: R = ρ (L/A)

R = (1.6 × 10⁻⁸) * (2 / 3 × 10⁻⁶)

R = 3.2 × 10⁻² Ω

Therefore, the resistance of the wire is 3.2 × 10⁻² Ω.

These are some important concepts and numerical examples from Chapter 3: Current Electricity. Make sure to practice additional numerical problems and refer to your textbook for a more comprehensive understanding of the topic.

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