Download - GRADE 8 PHYSICS MR. HUSSAM SAMIR ELECTRICITY
GRADE 8 PHYSICS MR. HUSSAM SAMIR
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ELECTRICITY
ELECTRIC CHARGE
PROPERTIES OF ELECTRIC CHARGE
Like charges repel. Unlike charges attract
We can make static electricity by induction
INDUCTION the process of charging a conductor by bringing it near another charged object and grounding the conductor
GRADE 8 PHYSICS MR. HUSSAM SAMIR
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An atom consists of protons, neutrons, and electrons. Some electrons can be moved away from their atoms.
Conductors cannot be charged by static electricity.
Lightning is a movement of electrons.
Dynamic electricity:-
Is the flow of electric charges through a conductor.
Potential difference is the work done to transfer a unit of charge between two points.
ELECTRIC CURRENT the rate at which electric charges pass through a given area
P.D =
J/COULOMB
OR VOLT
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The electromotive force (emf):-Is the total work done to transfer unit charge throughout the circuit,
outside and inside the source, it has units of volt.
The resistance (R):-It is the opposition of the conductor to the flow of electric current, it is measured in
ohm (Ω), it depends on:-
a. Length of the conductor. R α L b. Cross section area. R α 1 / A c. Type of material. d. Temperature.
Ohm’s law: - “The current intensity in a conductor is directly proportional to the potential difference
across its terminals at a constant temperature”
V = I R
Series Connection Parallel Connection
I is the same in all resistors.
The p.d (V) is distributed on all resistors
V = V1 + V2 + V3
I R = I R1 + I R2 + I R3
= I (R1 + R2 + R3)
Then Req. = R1 + R2 + R3
P.d (V) across all resistors is the same.
The total current is distributed among resistors
I = I1 + I2 + I3
321 R
V
R
V
R
V
R
V
Then
3R
1
2R
1
1R
1
eq.R
1
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The equivalent resistance is greater than the
biggest one.
Aim of this connection is to have large
resistance from a group of small resistances.
For a group of n equal resistors each of
resistance = r connected in series then
R = n x r
The equivalent resistance is smaller than the
smallest one.
Aim of this connection is to have a small
resistance from a group of large resistors.
For a group of n equal resistors each of
resistance = r connected in parallel then
R = n
r
For two resistors R1 and R2 in parallel
Req. = 21
21
RR
RR
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MAGNETISM
Any magnet has two poles North and South Pole.
Like poles repel, and unlike poles attract.
MAGNETIC DOMAIN a region composed of a group of atoms whose magnetic fields are aligned in the same direction
Some materials can be made into permanent
magnets as steel
Some materials can be made into temporarily
magnets as iron.
MAGNETIC FIELD a region in which a magnetic force can be detected
We can make a magnet by:- 1. Stroking.
2. Induction.
3. Electricity and called electromagnet.(DC current)
We can demagnetize a magnet by:- 1. Heating
2. Dropping
3. Hammering
4. Withdraw a magnet slowly from a solenoid carrying AC (alternating current)
GRADE 8 PHYSICS MR. HUSSAM SAMIR
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Magnetism from Electricity MAGNETIC FIELD OF A CURRENT-CARRYING WIRE
A long, straight, current-carrying wire has a cylindrical magnetic field
The right-hand rule can be used to determine the direction of the magnetic field
LOGIC GATES
1. NOT GATE
2. And gate
Input Output
1 0
0 1
A B Output
0 0 0
0 1 0
1 0 0
1 1 1
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3. OR GATE:
LED (Light emitting diode)
It emits light when electron passes through it.
DIODE
Change from AC (alternating current) to DC (direct current)
Allow the current to pass in one direction
LIGHT DEPENDENT RESISTOR (LDR):-
It is a resistor depending on the intensity of light.
As the intensity of light increases its resistance decreases, vice versa.
Buzzer Resistor Variable
resistor
Switch Battery Ammeter Voltmeter
A B Output
0 0 0
0 1 1
1 0 1
1 1 1