Static Electricity

Electricity :
is the flow of electrical charges or power

electric charge that can be transferred from one object to another

charge classified into two types :

positive charge
Negative charge

Conductors : are material in which charge can move easily

Insulators : are materials in which electric charge not easily
transported

Static electricity :
A type of electricity where electric charges build up on the
surface of an object without flowing
The electricity so produced by friction (rubbing) is called frictional
electricity or static electricity.
It occurs due to friction, conduction, or electrostatic induction
The diagram above shows a process called "charging by electrostatic induction
When a charged object is brought close to a neutral metal
sphere, charges redistribute inside the sphere

Example: Using a charged ruler to attract aluminum pieces.

How do charges interact?

Like charges repel (+/+ or -/-).
Opposite charges attract (+/-).
❌ Lightning: Can cause fires and injuries.
❌ Fuel Station Sparks: May ignite flammable vapors.
❌ Electronic Damage: Excess charges can harm delicate
components.
❌Dusts and germs are attracted by charged objects
How to stay safe?
✅ Use lightning rods.
✅ Grounding (discharging charges into the Earth).

1. Static electricity is used to paint cars.

2. It is used in computer printers
3. Static electricity is also used to remove pollution from smoke-
chimneys
 Lesson 2
Columb’s Law
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 Lesson 3
The repulsive and attractive

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 Lesson 4
The electric field

Intensity Symbol: E
E = Electric field intensity (N/C)
F = Force (N)q
Q= Charge (C)
K Coulomb’s constant (N·m²/C²)
d Distance (m)?

Electric field: The area around a charge where its influence is felt.
OR: The force per unit charge at any point in space.
It is a vector Quantity (has both magnitude & direction).
Electric fields arise from electric charges and changing magnetic fields.
Measured using an electrometer.
Strength depends on charge magnitude and distance.
Direction is from positive to negative charge

Field lines represent the force direction on a positive charge.

Properties: Start at positive charges and end at negative charges.
Never cross each other.
Denser lines Stronger field.
Same charges repel, opposite charges attract.

positive charge has electric field lines pointing outwards

while a stationary negative charge has electric field lines
pointing inwards.
Like charges repel → Field lines push away from each other.
Opposite charges attract → Field lines move toward each other.
Field intensity decreases with distance.
The electric field intensity is the electric field lines per unit area.

Charge magnitude: Larger charge Stronger field.

Distance: Field decreases as distance increases (inverse sQuare
law).
Medium: Different materials affect field strength.

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 Lesson 5
Capacitor
A capacitor : is an essential component in electrical circuits
It is used for storing charge, filtering currents, preventing sparks,
and tuning freQuencies
It consists of two parallel metal plates separated by an insulating
material

A capacitor: is a device that stores electrical energy by

separating charges.
When charged, one plate holds a positive charge and the other a
negative charge, creating a potential difference.
Two parallel metal plates separated by an insulator.

If the quantity of charge (in Coulombs) on one of its plates is (Q)

and the capacitance (in Farads) of capacitor is (C), the relation
between them is given by
 The Capacitor in a DC Circuit
When connected to a battery, electrons move from the negative
terminal to one plate, making it negatively charged.
The opposite plate loses electrons and becomes positively
charged.
Charging stops when the voltage across the capacitor eQuals the
battery voltage.
After charging, no current flows, as a capacitor blocks DC current.

The transfer of charge stops when the potential difference across

the plates equals the potential difference of the battery.
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 Lesson 1
Dynamic electricity
1. Conductors:

• They are the materials which allow electricity to flow easily through them.
• Examples: copper, silver, gold
• Note: Rich in free electrons

2. Insulators:

• They cannot allow electricity to flow easily through them.

• Examples: wood, paper, plastics, ceramics
• Note: Poor in free electrons

3. Semiconductors:

• They are materials with conductivities somewhere between conductors and insulators.
• Examples: silicon, germanium

4. Electric Current:

• The flow of electric charges of the conductor.

Summary:

• The electric current is due to the movement of free electrons in a conductor.

5. Types of Current:

1. Conventional Current:
The flow of positive charge from the positive to the negative.
2. Electron Current:
In opposite direction of the conventional current.
1. Electric Current Intensity (I):

• The amount of electric charges flowing per second through a conductor.

• Measured in: Ampere (A)
• Unit: Coulomb per second (C/s)

Formula:

Definition of Ampere:

• The current intensity if the quantity of electricity passing through any cross-section of a conductor in
one second is 1 coulomb.

2. Potential Difference (V):

• The work done in joules to transfer a unit charge (1C) between two points.

Measured in: Volt (V)

Unit formula:

• Measured by a voltmeter

Definition of Volt:

• The potential difference is 1 volt if the work done required to transfer a unit charge (1C) between two
points is 1 joule.
3. Electric Resistance (R):

• The opposition of the conductor to the flow of electric current due to friction.
• Measured in: Ohm (Ω)
• Formula:

Where:

• Measured by: Ohmmeter

Definition of 1 Ohm:
The electric resistance of a conductor is 1 ohm if it carries a current of 1 ampere when the potential difference
between its ends is 1 volt

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 Lesson 2
Ohm’s Law
Ohm’s law:
The current intensity flowing through a conductor is directly proportional to the potential difference
across it at constant temperature.

There is also a diagram showing vectors labeled V, R, and I, likely representing Voltage, Resistance, and
Current respectively.

Electric Power (Pw):

Definition:
It’s the rate of electrical energy consumed in the electric conductor.
Power is measured in:Watt (W)J
joule per second (j/s)V
volt × Ampere (v.A)

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 Lesson 3
Ohmic resistance
Ohmic Resistance refers to:
a material's ability to resist the flow of electric current.
Factors affecting it: material type, length, and cross-sectional
area.

The Factors affecting the Electric Resistance (at constant

temperature)
Where :
R: the resistance of conductor
l : the length of conductor
A: the cross sectional area of conductor
ρ e : the resistivity of the conductor (specific resistance)

Electric resistivity (Specific resistance) of a material (ρ e)

Resistivity (𝑒ρ Definition)
Definition:

Electric resistivity (also called specific resistance) is a measure of how strongly a material opposes the flow of
electric current.

Key Points:

• Unit:
Ohm meter (Ω·m)

• Concept:
It is defined as the resistance of a material 1 meter long with a cross-sectional area of 1 m² at
constant temperature.

• Interpretation:
o Low resistivity → the material readily allows electrical current to flow.
o High resistivity → the material resists the flow of current.

• Dependence:
o Resistivity depends on the material's nature.
o It also varies with temperature, even for ohmic materials
Electrical Conductivity (𝜎𝑒 Definition)
It is the reciprocal of resistivity
𝜎𝑒 eQual 1/𝜌𝑒

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 Lesson 4
Ohm’s law for closed circuit
Electromotive Force (emf)

Conceptual Analogy:

In an electric circuit, there must be a device (like a battery or power supply) that plays the same role as a water pump in
a water fountain — it pushes electric charge through the circuit.

Definition:

The electromotive force (emf) is the influence that causes current to flow in a circuit.
Despite the name, emf is not a force, but rather an energy-per-unit-charge quantity.

Formal Definition:

The emf of a cell is the total work done (both inside and outside the cell) to transfer an electric charge of 1 coulomb
through the entire electric circuit.

Unit:

Volt (V)
(Same as joules per coulomb: 1 V = 1 J/C)

Internal Resistance (r)

It is the resistance inside the battery.
It opposes the flow of current.
Causes a loss of voltage inside the battery
✅ Ideal Source

• The potential difference (V) across an ideal source is equal to the emf (ε).
• This is because an ideal source has zero internal resistance.

Real Source

• The potential difference (V) across a real source is less than the emf (ε).
• This is due to the presence of internal resistance rrr, which consumes part of the energy.
• As current flows, there's a voltage drop inside the source

the emf of the total source divided by the total (external plus internal) resistance of the circuit.
I Req =V = the terminal voltage
I r = the potential drop across the internal resistance
Note
For real source the terminal voltage is less than the emf of the source due the potential drop
across the internal resistance
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 Lesson 5
Connection of resistors

Two ways to connect res istors:

Series connection ➔ Increases
total resistance.
to obtain a higher resistance

Parallel connection ➔ Decreases total resistance.

to obtain a small resistance

Resistors in Series
1)The current through all the resistors is the same

2) The potential difference is split (divided)

3) The eQuivalent resistance is greater than the greatest

resistance
The higher the resistance, the higher the potential difference
(v α R at constant the current) (Series)
The higher the resistance, the lower the current that is flowing
through it (I α 1/R at constant the potential difference)(Parallel)
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