Musab Bin Omair Sec. ind. School for Boys
Physics department/Second semester (2011-2012)
Extra sheet
Student name :- …………………………………………………………….
Date /
5
/2012
 Electric current: is the flow of charges through aconductor
1. Electric current intensity is the rate of charges that flow through
conductor.
2. Its symbol is (I )
3. The equation to find it is I =
𝑄
𝑡
A
4. The SI unit is
Ampere = couluomb/ second
5. It is measured by ammeter
6. The ammeter should connected in sereies
 Potential difference:
1. Potential difference is the work done to transfer 1coulomb between
two points.
2. Its symbol is P.D. ( V)
3.The equation to find it is V =
𝑊
𝑄
4. The SI unit is Volt = joule/ coulomb
5. It is measured by voltmeter
6. The voltmeter should connected in parallel
V
 Electro motive Force :
1. It is define as the potential difference between the two poles of dry
cell when the circuit is opened .
2. Its symbol is E.M.F
3. Its SI unit is volt
4. The equations to find it e.m.f = I ( R + r)
5. It is measured by voltmeter
 Resistance:
1. Resistance is the opposition of passage of current.
2. Its symbol is R
3 .The equation to find it is R =
1
𝑉
𝐼
3. The SI unit is ohm Ώ
Ohm’s law: The electric current intensity is directly proportional
with the potential difference.
1.The equation V = I X R
2.The SI unit is Volt = Ampere X ohm
Electric power
Power is the rate of energy transfer (the energy that consumed in one
second.
1. Its symbol is P = VXI = I2 X R
2. The equations to find it :a)
3.SI unit is Watt
Resistivity
It is resistance of conductor has length = 1m and cross section area
= I m 2 =unit area.
1. Its symbol is
ρ=
2. The equations to find it ρ =
𝑅𝐴
𝐿
3.Measuring unit is ohm.m
The factors affect the resistance
Temperature
Length
Cross sectional
area
material
By increasing temperature resistance
increases
By increasing length resistance increases
By decreasing area resistance increases
Resistance depends on type of material
Compare between series and parallel resistance connections:
Connection of resistance in Series
Connection of resistance in
parallel
the net resistance is always greater than
that of any of the individual resistors
the net resistance is always Smaller
than that of any of the individual
resistors.
2
The current through each resistor is the
same. (constant)
The .voltage across each resistor in
parallel is the same(constant)
The total voltage across the resistors is
the sum of the voltage across the
separate resistors.
The current in the main circuit is the
sum of the currents in each of the
parallel branches .
Vtotal =.V1 + V2 + V3
I total = I1 + I2 + I3
𝟏
𝟏
𝟏
=
+
𝐑𝐓 𝐑𝟏 𝐑𝟐
RT = R1 + R2+ R3
t
I
V
P
I
ρ=
V
𝑅𝐴
𝐿
RT = R1 + R2+ R3
𝟏
𝐑𝐓
3
=
𝟏
𝐑𝟏
+
V
W
Q
𝟏
𝐑𝟐
+
𝟏
𝐑𝟑
Q
I
R