Nootan Kumar Mittal ISC class 12 PHYSICS Chapter 5 Electric Resistance and Ohm's Law( part I)

               Chapter 5

Electric Resistance and Ohm's law.

*Electric current

Rate of flow of charge.

(I)=charge flow/time

I = Q/T

Iavg =ΔQ/ΔT=dq/dt

Current(I) does not follow vector law of addition .

 " Current is a Tensor Quantity "

*  Electrical resistance.

Property of a material to obstruct the flow of electric current.

Unit of Resistance=Volt/Amper= ohms  Ω

I= Vd  en A

Vd=drift velocity of electron.

m=mass of electron

l= length of conductor

=Average relaxation time.

n= number of free electron per unit volume.

Free density

A=Area of cross section.

*Effect of temperature on Resistivity or Resistance.

*Colour code of carbon resistors.

1) Alloys- Nichrome manganin constantan 

Resistivity nearly Independent of temperature.

1)Limitation - very high resistance cannot be obtained practically.

2) Carbonn register- Very high resistance very small in size. They are so small cannot see value of their resistance.

We use colour coding of resistance value.

conceptual question

1)

2)

Shortcut trick off colour coding

*Current density.

* Ohm law

All physical condition remaining constant (like temperature)a conductor is directly proportional to the current flowing through the conductor.

R -resistance of conductor constant for ohmic condition

M =man of i  - constant.

L= length of conductor

N.=Number of free electron

E =charge on electron

A=Area of cross section

*Ohm's law in vector form.

Prove

Non-ohmic conductor.

Semi conductor

*Combination of resistance.

1) Series combination

2) Parallel combination.

- Conceptual Question -

1.

2. Find equivalent resistance between A and B.