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Electric Field

the space or region around a charge particle

Electric Field

it has a property that any charged particle placed in it will experience an electric force.

Michael Faraday

proposed the idea that an electric field exist at any position on a charge.

Michael Faraday

he introduced the use of electric lines of force to map out an Electric Field.

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1. Lines of force starts from positively charged particle and ends on the negatively charged particle
2. Lines of force repels each other sideways. They do not intersect nor break as they pass from one charge to another.
3. The greater the lines of force, the stronger the electric field.
4. The direction of the electric field at a point is the same as the direction of the tangent to the line of force at that point.

Line of force have the following properties:

outwards or away from

The direction of the electric field on a positively charged particle is ___________ the charge.

negatively

The direction of the electric field on a ____________ charged particle is towards itself or inwards

Electric Field

is not a force

same direction

positive test charge will experience an electric force in the (---------) as the electric field.

opposite direction

negative test charge will experience an electric force in the (----------) as the electric field.

Electric Field Lines

are an excellent way of visualizing electric fields.

Electric Field Lines

they were first introduced by Michael Faraday himself.

Electric Field Lines

is an imaginary line or curve drawn through a region of empty space so that its tangent at any point is in the direction of the electric field vector at that point.

Electric Field Lines

the relative closeness of the lines at some place gives an idea about the intensity of electric field at that point.

Electric Dipole

opposite signs but equal magnitude

Two Positive Charges

with equal magnitude

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Ø  One charge (Q1) creates an electric field over by another charge (Q2).

Ø  That charge feels a force and vice versa.

Ø  Any charge that is placed in the electric field will experience a force.

Ø  The strength of this field at a point known as the Electric field intensity, is the cause of the force that a test charge will experience when placed at that point.

How electric fields work?

Electric Field Intensity

is the measure of the strength of an electric field at any point.

Electric Field Intensity

it is equal to the electric force per unit charge experienced by a test charge which is placed at that point.

Electric Field Intensity

in defining this, physicist use a unit positive charge as the test charge.

Electric Potential

is the amount of work needed to move a unit of charge from a reference point to a specific point inside the electric field.

Electric Potential

amount of work done to bring a positive charge (test charge) form infinity to the point charge

Electric Potential

electric potential (V) is defined as the electric potential energy (U), per unit charge (q).

*V = U/q*

Formula of Electric Potential

volts ( 1 volt = 1 J/C)

unit of Electric potential

Electric Potential

related to electric potential energy & E-field

*V = k Q/r*

Formula for Electric Potential Energy

positive

The potential due to a positive charge is ______.

negative

The potential due to a negative charge is ______.

Electric Potential & Electric Potential Difference

We always use the sign of charge in getting these.

Electric Potential Difference

is the difference in the electric potential between the final and initial position when work is done upon a charge to change its potential energy.

*∆V = Vf - Vi*

formula for Electric Potential Difference

Work

product of the magnitude of displacement on an object and the component of the force parallel to the displacement.

Work

product of displacement (d) and a parallel applied force (F).

Cosθ

is the angle between the force and displacement.

Kinetic Energy (K)

is the ability, or capacity to do work.

Potential Energy (U)

is the energy that could be used to do work. It is the energy due to position.

Work (W)

product of displacement (d) and a parallel applied force (F).

Electric Potential Energy

the energy needed to move a charge against an electric field.

Electric Potential Energy

describes how much stored energy a charge has, when moved by an electrostatic force.

(W = qEd)

The work done by the electric field on the charge is

Q

charge that creates E-field

q

test charge

Capacitors

is a device that stores electric charge/energy.

Capacitors

consists of two conductors separated by air, a vacuum or an insulator.

Capacitors

consists of two conductors (known as plates) carrying charges of equal magnitude but opposite sign.

Capacitance

depends on the geometry of the capacitor and on the material, called a dielectric, that separates the conductors.

Dielectric

is an insulating material or a very poor conductor of electric current.

Ø  A capacitor stores energy in the form of an electric field that is established by the opposite charges on the two plates.

Ø  A capacitor obeys Coulomb’s law: a force exists between two-point source charges that is directly proportional to the product of the two charges and inversely proportional to the square of the distance between the charges.

How a capacitor stores energy

potential difference DV

A ______________ exists between the conductors due to the presence of the charges.

Capacitance

is the ability of a capacitor to store charges

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1. Area of plates
2. Distance between the plates
3. Insulating material or dielectric between them.

Factors affecting capacitance:

Area of plates

the bigger the area of plates, the greater is the capacitance.

greater

the bigger the area of plates, the ______ is the capacitance.

Distance between the plates

the closer the plates to one another, the greater the capacitance.

closer

the _______ the plates to one another, the greater the capacitance.

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1. Size of the capacitor (A, d)
2. Geometric arrangement
 Plates
 Cylinders
3. Material between conductors
 Air
 Paper
 Wax

Factors affecting capacitance:

a) Full plate area = more capacitance

b) Reduced / less plate area = less capacitance

Capacitance is directly proportional to plate area (A):

Full plate area & Less distance between plates

more capacitance

Reduced / less plate area & More distance between plates

less capacitance

a) Less distance between plates = more capacitance

b) More distance between plates = less capacitance

Capacitance is inversely proportional to the distance (d) between the plates

Parallel-Plate Capacitor

the capacitance of a device depends on the area of the plates and the distance between the plates

8\.85×10-12 C2 /N·m2

permittivity of free space

*(Ceq = C1 + C2 + C3 + …)*

Capacitors in Parallel formula

*( 1/Ceq =  1/C1 + 1/C2 + 1/C3 + …)*

Capacitors in Series formula

Electrodynamics

the science of this deals with electrical charges in motion.

Electric Circuit

a closed conducting path where charges flow.

* Current
* Resistance
* Voltage

3 Essential Elements in an Electric Circuit:

1. A source of energy
2. A closed path
3. A device which uses the energy

All electric circuits have three main parts:

Electric Charges

are made up of positive charges (protons) and negative charges (electrons).

The battery in a circuit gives energy to the electrons and pushes them around a circuit, from the negative terminal of the cell, round the circuit and back to the positive terminal of the cell.

How does electricity flow?

Current (I)

produced when charges flow in a circuit

Current (I)

is the flow of charges per unit time.

Current (I)

its SI unit is ampere (A), which is equivalent to one coulomb of charge per second.

Current (I)

is a measure of the rate of flow of electric charge through a circuit.

Current (I)

a large current means a faster rate of flow.

Current (I)

can be changed by increasing or decreasing the voltage of the circuit.

A - Ampere

UNIT OF Current (I)

Resistance

components in a circuit may reduce the size of the current. All wires and components resist current.

1. Conventional Current
2. Non-conventional Current

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or

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1. Direct Current (DC)
2. Alternating Current (AC)

There are two types of current based on the movement of the charge carriers:

Conventional Current

has holes or positive charges as moving charge carriers.

Non-conventional Current

involves the opposite – moving electrons.

Direct Current (DC)

current flows in one direction. Example: Battery

Alternating Current (AC)

current reverses direction many times per second. This suggests that AC devices turn OFF and ON. Example: Wall outlet (progress energy)

Resistance (R)

it describes the opposition of a material to the flow of charge carriers.

Resistance (R)

is a measure of how hard it is for electrons to move in an electrical circuit.

Conductivity

the reciprocal of resistivity

Metals

has low resistivity, that’s why they are good conductors.

Materials with high resistivity

are usually insulators.

Resistor

is a component designed to reduce the current.

Variable Resistor

has a resistance that can be changed

Resistor

a fixed this has a resistance that remains the same.

Resistor

are also used to control the current in electric circuits (many domestic appliances use resistance to transfer electrical energy to heat and light energy. As current is passed through the metal element in this kettle, resistance causes the metal to get hot and so boils the water.)

variable resistor

has a resistance that can be changed

fixed resistor

has a resistance that remains the same

* Material


* Thickness
* Length
* Temperature

The resistance of a wire depends on many factors:

*(V = I × R)*

Ohm’s Law formula

Ohm’s Law

may be applied to the whole circuit or to a particular part of a circuit.

*(IT = E/RT )*

Ohm’s Law: Applied to whole Circuit

*(I = V/R)*

Ohm’s Law: Applied to a Portion of a Circuit