Current Electricity | Digital Notes
Charge(motion)
-acclerated
-non acclerated
In - chapter - discuss about the behaviour of charge in accleration.
Theories - in electrostatic is all only non acclerated change.so,we
cannot apply laws of electrostatic here.
Current
It is an event in which charge cross through any cross section with respect to
time.
SI Unit Amp = 1c/s
Current[ of [two types]
-Instantineous current
-Average Current
Instantineous Current
It is current that is defined for a particular instant of time (the time
interval is treated to infinite small).
I = dq/dt
Average Current
This is a current which is defined for average interval of time.
Microscope View of conductor without batter
-electrons inside (Brownian Movement)
-random motion effective charge passed is zero, so no current is flowing
through out the conductor.
When a Conductor is connected with a battery then
pd. is developed across conductor which give rise to electric field
inside conductor.
Now due to this electric field force starts acting on electron due to this
force as well as due to random motion electron starts gig - gag path and drift
towards left from cross section which give rise to current in circuit.
Drift velocity
This is the effictive speed which provide effective displacement to an
electron.
| Vd | = l/t
Note:- Drift speed is a average speed.
Relaxation time(T)
The oppose of flow of current is known as Resistance.
Relaxation time is defined as average time b/w two sucssive collisions.
Q)If temp. of conductor is increased comment on T and Resistance?
Ans - When temp. of conductor is increased Resistance increases as a result
more number of collosion will be taking place due to this the avg. time b/w
two colloisions decreases and T also decreases.
Mathematical derivation of drift Velocity
Relation b/w Vd 2 'I'
I = neAVd
Derivation of ohm's law
-Ohms law is dependent on particular temperature of conductor due to its
dependency on relaxation time.
-Resistivity is a property of conductor which is independent of shape and size
of conductor and only depends on properties of conductor.
-Resistance of conductor depends on shape and size of conductor.
Note:-In r = (rho)l/A l is length along the direction of current flow, of conductor.
-A is the Area of conductor perpendicular to direction of current flow.
Current Density (J)
- J has direction along direction of current.
Note:- Prerequisite Knowledge
We have three type of physical quantities Scalor,Vector,and Tensor, Tensor
is a physical quantity which has direction but it do not follow vector
addition law.
|J||A|Cos theta = |I|
Variation of Resistance with temperature
If temperature increases resistance increases.
Combination of resistance
- To solve combination of resistors we have 5 techinique.
1.Point Method
2.Wheatstone bridge
3.short circuit
4.Vertical Symmetry
5.Horizontal Symmetry
EMF (Electro Motive Force)
The electric field due to potential difference of battery is rightward as
result force due to electrostatics on a proton is right world.
When observed in a close circuit it is force proton is moving leftward,so
there must be a force generated by battery due to ongoing chemical rxn which
drive proton left words.This force is known as battery force.
The force acting on proton due to battery does a work on proton (+ve work done
) due to this work done energy is given to proton this energy is k/a electro
motive force.
Emf is defined as work done per unit charge on carrying charge from -ve
plate to +ve plate
Note:- Its unit Joule per Columb J/C = volt
We know a charge is passing through connecting wire there is loss of energy in
force of heat.
We represent this loss with the help of internal resistance of a battery,
So energy delivered to load resistance in closed circuit is less emf.
Battery
Note :- Battery provide energy to load resistance with the help of proton or electron.*So,proton is acting as a energy carrier.
Note :- EMF of a battery is independent of load resistance.
*p.d of battery do depend on a load resistance.
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