what do you mean by thermal velocity and drift velocity of moving electrons in cunducter ? drive the relation between drift Velocity and electric current.
Answers
Answer:
The average velocity of all the free electrons in the conductor is called the drift velocity of free electrons of the conductor. When a conductor is connected to a source of emf an electric field is established in the conductor, such that E=
L
V
When V= potential difference across the conductor and L=length of the conductor
The electric field exerts an electrostatics force '−Ee' on each free electron in the conductor
The acceleration of each electron is given by
a
ˉ
=−
m
e
E
Where, e=electric charge on the electron and
m=mass of electron
Acceleration and electric field are in opposite directions, so the electrons attain a velocity in addition to thermal velocity in the direction opposite to that of electric field.
v
d
=
m
c
E
τ...............(i)
E=
L
−V
...........(ii)
Where τ=relaxation time between two successive collision
Let n=number density of electrons in the conductor
N0. of free electrons in the conductor =nAL
Total charge on the conductor , q=nALe
Time taken by this charge to cover the length L of the conductor,
t=
v
d
L
Current I=
t
q
=
L
nALe
×v
d
=nAev
d
Using equation (i) and (ii), we get that
I=nAe×(−
mL
e(−V)
τ)
=(
mL
ne
2
A
τ)V