This document discusses how electric current flows in metallic conductors. It explains that metals contain free electrons that are not bound to any particular nucleus and can move throughout the material. When an electric field is applied, the free electrons drift in the opposite direction of the field, constituting an electric current. Their drift velocity depends on factors like the electric field strength, temperature, and material properties. The document also introduces concepts like relaxation time and how increasing certain variables affects resistance.

1.  Presented By
 Vasudev Shrivastava
 P.G.T. Physics
 J.N.V Nowgong District Chhatarpur M.P.

2.  Sub topics
 Electric current through conductors
 Drift velocity.
 Electric current in terms of drift velocity
 Resistivity and resistance
 Ohm law
 Factors dependence on resistance and
resistivity of materials.

3.  After completion of topic
 The student will be understand how
electric current flows in conductors
 They will be understands that why
electron moves with average velocity in
conductors
 The students will be establish relation
between drift velocity and electric
current.
 The students will establish relation
between resistivity and relaxation time .

4.  State coulomb law.
 The electric force between two static charges is directly proportional to
the product of magnitude of charges and inversely proportional to the
square of distance between them.
 What is electric current?
 The rate flow of electric charge is known as electric current.
 What is current density?
 The current per unit area of the cross section of a conductor, which is
perpendicular to the direction of current, is known as current density.
 How the current flow in electrolytes?
 The electric current flow in electrolytes due motion of positive and
negative ions.
 Why electric current does not flow in insulators?
 In insulators their no free charge so that electric current does not flow.
 How the electric current flows in metallic conductors?
 No answer
 Do you know about drift velocity?
 No answer

5.  First we discuss formation of crystal , during formation of
crystal of a metal a large no of atoms are close to gather they
exchanges their energies . In outer orbit of atoms there are
two types of electrons who attains lower energy are termed
valence electron.
 These valence electrons remains shared between adjacent
atoms to form a bond.
 Another type of electron in outer most of orbit who attains
higher energy state are termed as free electron.
 The free electrons do not remains bound to a particular
nucleus but they can move any where in metal volume.
 In normal state, free electrons remains uniformly distributed
over the volume, although always in a state of motion.
 The random motion of free electrons is called thermal motion

7. Due to thermal motion of free electrons no
electric current will flow in circuit due to no
net flow of charge in any direction .

8. When electric field is applied then the free electrons are start to moving in
opposite direction of electric field, random motion is still associated with these
electrons but to addition to that a net flow develops in opposite to applied
electric field.

9.  When some electron accelerated opposite to
electric field they acquires kinetic energy but
due to collision with ions they losses their
energy. the result of losses in energy is
inform of heat, hence to maintain the flow of
charge we need to supply energy
continuously to these particles

16. (i) E=V/L
(ii) a= - Ee/m the negative sign indicated that
electron is accelerating opposite to direction
of electric field.
(iii) Positively charged nuclei also experience
force in the direction of electric field but it
does not moves.
(iv) The conventional direction of electric
current is along direction of flow of
positive charge.
(v) Relaxation time The average time interval
between two successive collisions, of
electrons, when current is flowing through a
conductor is known relaxation time.

17.  Drift velocity : the average velocity with which
free electrons get drifted in the direction
opposite to applied electric field is known
drift velocity.
 Drift velocity depends up on of electric field.
Nature of matter, temperature , on increase
of temperature electrons are frequently
collides so that relaxation time will decreases
which reduces drift velocity .
 vd =- eEt/m ,t represent relaxation time

18.  Drift velocity : the average velocity with which
free electrons get drifted in the direction
opposite to applied electric field is known
drift velocity.
 Drift velocity depends up on of electric field.
Nature of matter, temperature , on increase
of temperature electrons are frequently
collides so that relaxation time will decreases
which reduces drift velocity .
 Vd =- eEt/m ,t represent relaxation time

24.  Find the relaxation time of conduction
electrons in a metal of resistivity 1.54 × 10-
8 Ω-m, if the metal has 5.8 × 1028 conduction
electrons/m3.
 Sol: Given data are:
 Resistivity of the metal, ρ = 1.54 × 10-8 Ω–m
 Number of conduction electrons, n = 5.8 ×
10 28/m3
 Relaxation time, τ = ?

25. 02 Calculate the mobility of the electrons in copper obeying
classical laws. Given that the density of copper = 8.92 ×
103 kg/m3, Resistivity of copper = 1.73 × 10 –8 ohm-m, atomic
weight of copper = 63.5 and Avogadro’s number = 6.02 ×
10 26 per k-mol.
Sol: Density of copper, D = 8.92 × 103 kg/m3
Resistivity of copper, ρ = 1.73 × 10–8 ohm–m
Atomic weight of copper, W = 63.5
Avogadro number, NA = 6.02 × 1026 per K-mol
Mobility μ = ?

26. Which of the following factors would decrease the resistance through an
electrical cord?
(a)Increasing the length of the cord
(b)Increasing the resistivity
©Decreasing the cross-sectional area of the cord
(d) Increasing the cross-sectional area of the cord

27. (c ) Increasing the cross-sectional area of the cord
Explanation:
The equation for resistance is given by R=ρl/A.
From this equation, we can see the best way to decrease resistance is by
increasing the cross-sectional area, A, of the cord. Increasing the length, L, of the
cord or the resistivity, ρ, will increase the resistance

28.  Electric current flow with in conductor is due to?
 due to Motion of free electron .
 How does the drift velocity of electron in metallic
conductor vary with temperature?
 On increasing of temperature relaxation time will
decreases ,the drift velocity is directly
proportional to relaxation time hence it will
decreases on increasing of temperature .
 If potential difference across a given copper wire
is increases .What happen to the drift velocity of
the charge carriers?
 Increases.

30.  metal a large no of atoms are close to gather
they exchanges their energies . In outer orbit
of atoms there are two types of electrons who
attains lower energy are termed valence
electron.
 No role of valence electron on conduction of
current.
 Electric current flows due to motion of free
electrons.