Current Electricity:Class 12 Physics NCERT Chapter 3

Key Features of NCERT Material for Class 12 Physics Chapter 3 –  Current Electricity 

In this Chapter 2:Electrostatic Potential and Capacitance we will learned potential energy of the system of charges.In this Chapter 3:Current electricity we will learn about electricity,some laws and rules regarding electricity.

Quick revision notes

1. The coordinated pace of stream of electric charge through any cross-segment of a channel is known as electric flow. 

In the event that ∆Q charge streams in time ∆t, at that point current whenever t is 

NOTE: Current is a scalar amount. 

I is toward stream of positive charge and inverse to the bearing of stream of negative charge. 

SI unit of current is ampere and is spoken to by A. 

2. The current thickness at a point in a conductor is the proportion of the current by then in the conductor to the region of cross-segment of the conductor by then gave the zone is held typical to the bearing of stream of current

NOTE: Current thickness is a vector amount. 

3. Flow of Electric Charge in Metallic Conductors in Metallic Conductors Among the solids, all metals are acceptable conveyors of power. The reason for conductance is free electrons. 

In Case of a Solid Conductor (i.e. Cu, Fe, Ag, etc) molecules are firmly bound to one another. There are huge number of free electrons in them. 

In Case of a Liquid Conductor Like electrolytic solution,  there are positive and negative charged particles which can proceed onward applying electric field. 

4. Drift Velocity It is characterized as the normal speed with which the free electrons move towards the positive finish of a conveyor affected by an outer electric field applied.
5. Electric current in terms of drift velocity
6. Current density at any place of conductor,

j = nevd

where, j is a vector quantity.

7. Mobility The proportion of float speed of electrons and the applied electric field is known as mobility.
8. Ohm’s LawAt steady temperature, the potential contrast V over the finishes of a given metallic wire (channel) in a circuit (electric) is straightforwardly relative to the flow moving through it

The variety of current w.r.t. applied potential contrast is appeared with the assistance of following diagram. 

V = IR 

where, R = opposition of conductor 

No impact of V and I on R in light of the fact that as V increment, I increment however R continues as before. 

9. Resistance of a Conductor  Mathematically, it is the proportion of potential distinction applied over the finishes of conductor to the current moving through it. 

=> R = V/I

SI unit is ohm (Ω).

Resistance can likewise be composed as, 

R =ρ L/A

where, L = length of the conductor, A = area of cross-section and ρ = constant, known as resistivity of the material. It relies on nature of the material. 

10. Relationship between resistivity and relaxation time
11. 
12. Temperature Coefficient of resistance is given by
13. Conductivity It is characterized as the corresponding of resistivity of a conductor. 

It is communicated as, σ = 1/ρ 

SI unit is mho per meter (Ω-1/m). 

14. Superconductivity The resistivity of certain metal or amalgam drops to zero when they are cooled under a specific temperature is called superconductivity. It was seen by Prof. Kamerlingh in 1911. 
15. Connection between flow thickness (j), electric field (E)and conductivity (σ ) is 

j = σ E 

16. Some Important Units
17. 17. On the off chance that a conductor is extended or packs to n seasons of unique length, at that point 

l’ = nl => R’ = n2R 

where, R’ = new obstruction and R = unique opposition. 

18. Colour Code of Resistance The shading code on carbon resistor stays as coaxial rings. 

The primary band speaks to the main noteworthy figure, second band speaks to second critical figure and third band speaks to multiplier (for example intensity of ten). The fourth band speaks to resilience. 

19. Combinations of Resistance There are two kinds of opposition mixes. 

(I) Series Combination In this mix, various protections are associated start to finish. 

Equal obstruction can be gotten as the recip

NOTE: The complete obstruction in the arrangement mix is more than the best opposition in the circuit. 

(ii) Parallel Combination In this mix, first finish of the apparent multitude of protections are associated with one point and last finish of the apparent multitude of protections are associated with other point. Comparable obstruction can be gotten by the recipe 

NOTE: The absolute opposition in equal mix is not exactly minimal obstruction of the circuit. 

20. On the off chance that n indistinguishable resistors every one of opposition r are associated in 

(I) arrangement blend, Req = nr 

(ii) equal blend, Req = r/n