Current Electricity.pptx

Thursday, June 22, 2023 Current Electricity – Hr. Sec. Second Year 1
Higher Secondary – Second Year
CURRENT ELECTRICITY
UNIT
02
By
RAJENDRAN M, M.Sc., B.Ed., C.C.A.,
P.G.TEACHER IN PHYSICS

Thursday, June 22, 2023 2
Learning Objectives:
Current Electricity – Hr. Sec. Second
Year
In this unit, the student is exposed to
Flow of charges in a metallic conductor
Ohm’s law, electrical resistance, V-I characteristics
Carbon resistors and combination of resistors
Kirchhoff’s laws - Wheatstone’s bridge and its applications
Electric power and Electric energy
Heating effect - Joule’s law – applications
Thermoelectric effects – Seebeck effect – Peltier effect – Thomson effect

Year
INTRODUCTION
In unit 1, we studied the properties of charges when they are at rest. In reality,
the charges are always moving within the materials. For example, the
electrons in a copper wire are never at rest and are continuously in random
motion. The motion of charges constitutes ‘electric current’. Current electricity
is the study of flow of electric charges. It owes its origin to Alessandro Volta
(1745-1827), who invented the electric battery which produced the first steady
flow of electric current. Modern world depends heavily on the use of
electricity. It is used to operate machines, communication systems,
electronic devices, home appliances etc.,

Year
2.1 ELECTRIC CURRENT
Matter is made up of atoms. Each atom consists
of a positively charged nucleus with
negatively charged electrons moving around
the nucleus. Atoms in metals have one or more
electrons which are loosely bound to the
nucleus. These electrons are called free
electrons. These free electrons move randomly
throughout the conductor at a given temperature.

Year
Positive charge flows from region of higher
electric potential to region of lower electric
potential and negative charge flows from
region of lower electric potential to region
of higher electric potential.
When a potential difference is applied by
the battery across the ends of the
conductor, the free electrons drift
towards the positive terminal of the
battery, producing a net electric current.
The electric current in a conductor is
defined as the rate of flow of charges
through a given cross - sectional area.
I =
𝑄
𝑡
(𝑜𝑟) 𝑖 =
𝑑𝑄
𝑑𝑡
.
The SI unit of current is ampere (A).
It is a scalar quantity.
One ampere of current is equivalent to
1 coulomb of charge passing through
a perpendicular cross section in
1 second. [1 A = 1 Cs-1]

Year
2.1.1 CONVENTIONAL CURRENT
In an electric circuit, arrow heads are used to
indicate the direction of flow of current.
By convention, this flow in the circuit should
be from the positive terminal of the battery
to the negative terminal. This current is
called the conventional current or simply
current
2.1.2 DRIFT VELOCITY
Drift velocity ( 𝒗𝒅 ):
If there is no electric field, all the free electrons in
a conductor are moves in random directions. As a
result, no net flow of electrons in any direction and
hence there will not be any current. If the
conductor is subjected to an electric field (𝐸 ) free
electrons experiences a force given by,
F = − eE ………….(1)
So all the free electrons are accelerated in a direction
opposite to the field. By Newton’s second law 𝐚 =
𝐅
𝐦
;
=
−𝐞𝐄
𝐦
……….. (2)
But the positive ions scatter the electrons and
change its direction of motion. So they move in
zigzag path.
In addition to the zigzag motion due to collisions,
the electrons move slowly along the conductor in a
direction opposite to that of 𝐸.

Year
This average velocity acquired by the free
electrons inside the conductors, when it is
subjected to the electric field is called drift
velocity (𝒗𝒅)
The average time between successive
collisions is called the mean free time or
relaxation time (𝜏).
Hence the drift velocity is given by, 𝒗𝒅 = 𝑎𝜏 ;
𝑣𝑑=
−𝑒𝐸
𝑚
𝜏 = −𝜇𝐸 ;
𝑒τ
𝑚
= 𝜇 → mobility of electrons
The magnitude of the drift velocity acquired by
the free electron per unit electric field is called
mobility. 𝜇 =
𝒗𝒅
𝐸
. It unit is m2V-1s-1

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https://amrita.olabs.edu.in/?
sub=1&brch=6&sim=22&cnt=1

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https://amrita.olabs.edu.in/?su
b=1&brch=6&sim=147&cnt=4

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https://amrita.olabs.edu.in/?
sub=1&brch=6&sim=146&cnt
=739

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https://amrita.olabs.
edu.in/?sub=1&brch=
6&sim=231&cnt=4

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Thank you !
Year

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