2. Introduction
Electric current& formula& S.I. unit& quantity
Types of charges
Moving charges is a current or not a current
Electric current in a conductor
Direction of electric current
How electric current measures?
How Small quantities of electric current are expressed?
Effects of current
Sample problem
Drift velocity
Current density
Sample problem
Types of current
3. Electric current
Def: The current is the rate at which
charge flows through surface.
Meaning: flow of electrons
Iavg=∆Q/∆t
I ins= dQ/dt
S. I unit is 1A
IA=1C/s
Electric current is a scalar quantity.
4. Types of charge
There are two
types of charge.
Positive charge.
Negative charge.
5. Moving charges as a current or
when moving charges is not
current Its described as a
steam of moving
charges.
May range very small
currents such as the
nerve impulse to a
large as the solar wind
emitted by the sun.
There must be a “net”
flow of charges
towards one direction.
When there is no net
flow of charge even
though there are
actual movement.
Examples:
Electrons of a copper
conductor in absence
of electric potential.
Electrons just move
randomly the charge
flowing to one
direction is equal to
those flowing to the
other direction
6. ELECTRIC CURRENT IN A
CONDUCTOR
Depend upon potential difference
Material in which charges passing
7. Direction of electric current
Movement of
electron along the
conductor.
Electrons are
negatively charged.
9. How small quantities of
electric current are
expressed?
The small quantities of electric current
are expressed in :-
1. Milliampere ( 10 -3A )
2. Microampere ( 10 -6 A)
10. Effects of electric current
1. Heating effect (H=I2RT)
2. Magnetic effect: produces magnetic
field depend on value of current and
distance.
3. Chemical effect: dilute sulphuric aid
and copper sulphate are used as
electrode. Which conduct electricity
due to some chemical reactions.
12. ELECTRIC CURRENT
SAMPLE PROBLEMS
A wire carries a current of 0.2 ampere.
How many electrons passes in 2 s?
When charge is 4microcoloumb and time
is 2 s. What is current?
14. CURRENT DENSITY
Current per unit of cross-sectional area of
a conductor.
A vector quantity with the same direction
as the motion of positive charge carriers.
15. SAMPLE PROBLEM
Question no 1
A 491 gauge copper wire has a nominal
diameter of 0.64mm. This wire carries a
constant current of 1.67A to a 4,910 watts
lamp. The density of free electron is
8.5*10*28 electrons/m3.Find the current
density and the magnitude of drift
velocity?
16. Types of current
Direct current: developed by Tomas
Alva Edison.
Graph is straight line.
Alternating current: developed by
Nekoola Tesla and George
Westinghouse, forming revalry with
Thomas Edison on War of the
Currents.
Graph is sinosoid.