Download 7TH CLASSES PHYSICS DAILY PLAN

10TH CLASSES
PHYSICS
DAILY PLAN
SUBJECT: ELECTRIC CURRENT
AIM: to understand the concepts of el.current and
resistance of a wire
DURATION: 120 min
REAL LIFE: batteries, resistors and their functions
in a simple el.circuit
PRESENTATION:
The free electrons in the conducting wire flow
under the action of the electric force, F=qE,
produced by the electric field. When charge flows
through a conductor an electric current is said to
exist in the conductor.
An electric current in a conductor is defined as
the quantity of the net charge that flows through any
cross-section of the conductor per unit time. If a net
charge q flows in a time t the current I is I=q/t
c/s = Ampere (A)
In our study of electric circuits we take the
direction of current from the positive to the negative
terminal of battery.
Example 1: A copper rod has a length L=10 m
and a cross-sectional area of 1mm2 (a) Find the
resistance of the rod, =1,7*10-8 ohm-m
Solution: A
L
Example 2 -- (a) What current flows through a 20ohm resistor when a potential difference of 40 V is
applied between its ends? (b) How many electrons
pass through the resistor per second?
Solution:
Temperature Variation of Resistance
RT=R0 (1+T) where RT is the resistance at
temperature T oC, Ro, is the resistance at 0 0C, and
 is called the temperature coefficient of resistance
and a measure of the increase in resistance per 1 0C
rise in temperature.
As the temperature rises the current read from the
ammeter decreases. Since voltage across the wire is
constant, a decrease of current implies an increase
of resistance according to ohm’s law.
Ex: 2,4,6,7,8 will be solved
+VTHE RESISTANCE OF A
CONDUCTOR
If we connect a copper rod and an iron rod, of
the same length and cross-section, to the terminals
of the same battery, the current in the copper rod
will be about six times larger than the current in the
iron rod. This shows that the current in a rod, or a
wire, depends not only on the voltage applied
between the ends of the wire but also on the degree
of opposition exists in the wire against the flow of
the electrons.
OHM’S LAW
From the experiments if we connect a rod to the
terminals of a battery, If we increase the voltage,
current will also increase so, I=V
The opposition against the flow of the electrons
is called the Resistance, R, of the wire.
The resistance of a wire is the voltage applied to
its ends, divided by the current that flows through
it, or
R=V/I (V/A)=ohm ()
The resistance of wire at a constant temperature
depends on three factors: its length, its crosssection, and the substance which is made of. The
resistance of a wire (made of specific material)
varies directly with its length and inversely with its
cross-section. That is R=L and R=1/A
Resistance of a wire
R=. L/A
HOMEWORK: pr.4, 5,6,11,12
MULTIMEDIA: serway3, akadem, sreway10, open
ph.2, basic48,
DEMONSTRATION:
EXPERIMENT:
TEACHER:
DIRECTOR: