# Formula booklet physics class 12 chapter Current Electricity

## Current Electricity formula are listed below:

The rate of charging flow in any part of the wire is called the electric current flowing through it.

Electric current (I) = q / t. Its SI unit is ampere (A).

Conventional electrical current direction is the direction of the positive charge motion.

The current is the same for all non-uniform cross-section conductor sections. Similar to water flow, charging flows faster when the conductor is small in the opposite direction and slows down when the conductor is more extensive in the cross-section so that the charging level remains unchanged.

When charging, q revolves around a circle with frequency f, equal power,

i = qf

(Metallic conductor current flows due to free electrons' motion while electrolytes and ionized gases flow now due to electrons and directions.)

### Types of Electric Current

According to both magnitude and direction electric current is of two types

1. Direct Current (DC) Its magnitude and direction do not change over time. A ceil, battery or DC dynamo are the most direct current sources.
2. Alternating Current (AC) An electric current whose magnitude change continuously and change its direction from time to time is called alternating current. The AC dynamo is a current exchange source.
• Resistance R= V/i

Where I = Strength of current

i = current

• Variati​on of resistance with temperature:

R = R0(1 + αΔT)

Where-Rt-resistance at temperature t°C,

R0-resistance at temperature 0°C,

α -temperature coefficient of resistance.

Conductivity = Reciprocal of resistivity or σ = 1/ρ = 1/RA

• Terminal voltage:

Case-1: When battery is delivering current

V = E – ir

Where – V-terminal P.D., E – emf of the cell, r-internal resistance of the cell,

R- external resistance.

Case-2 : When battery is charging

V = E + ir

• Kirchh​off’s laws:
1. Kirchhoff’s first law : ∑i = 0 at any junction
2. Kirchhoff’s second law : ∑i R = 0 in a closed circuit.
• The balancing condition for wheat stone bridge is p/q = r/s , Where P, Q, R and S are the resistances in the bridge
• Meter bridge

Where – x – unknown resistance of given wire, R – resistance in the resistance box, l1- balancing length from left end of the bridge to Jockey.

ρ=Lπr2X

Where - ρ-resistivity of the wire,

x-resistance of wire,

A – Area of cross section of the wire,

l-length of the wire.

• Potentio Meter:

Emf of the cell in the secondary circuit

Es = Iρ

(i) Comparison of emf’s of two cells

E1/E2 = L1/L2

Where – E1- emf of first cell, E2 – emf of second cell, l1 and l2-the balancing lengths of individual cells respectively.

(ii) For determination of internal resistance of cell:

r = R (L1 - L2)/L2

Do follow NCERT Solutions for class 12 Physics prepared by Physics Wallah. If any students need to take the online test to check their concepts or undertstanding then they can visit Quiz for Current Electricity.

Download the Pdf of class 12 formula bookle​t physics of chapter Current Electricity from the link given below