physics

What is a charge

It is the fundamental property of matter that causes particles to experience electrical force

This is shown as

e = 1.602 times 10^-19 ©

What is voltage and its formula

Voltage is the potential difference between two points making them move. This can be shown as

V = Ed

Current formula and meanin

I =Q/t

It is the rate of electric charge per unit of time

What is conventional current and electron flow

Conventional currents moves from positive to negative while electron flow goes from negative to positive

What is resistance

It is the opposition to the flow of electric current

Ohm’s law

V = IR

Voltage drop across a component equal to the current going through it by its resistance

Electric field meaning

An area of influences around charged particles within which other charges will experience a force shown as

E =FD

Coulomb’s law

F = K times Q1Q2/ r²

direction of positive and negative charges

Positive goes outwards and negative goes inwards

Formula for electric field in parallel plates

E =v/d

Force in electric fields

F = qE = q times v/d

3 one only works for parallel plates

q= charge experience the electric field

Yr 12 mod 6

Trajectories of charges in parallel plates

In projectile motion the only force is weight and objects will accelerate downwards. However this is the same for charges but except the force that replaces weight is F=qE

Therefore it goes towards the positive plate

How to do steps and tips

1. Set f=Qe= ma

2. Check suvat equations from mod 5

3. Solve

Fe goes towards the positive plate

And qe=mg

Work and energy formula

W=qv

(Derived from w= Fii times d

Tips for work

W=QV=KE= U

What is magnetic flux

It quantifies the total magnetic field passing through a defined area. In which only the components of the magnetic field that is parallel to the are vector is considered

Formula for magnetic flux

Phi = Bii times A

A = area vector component parallel to B (m²)

Bii = magnetic field strength

drawing flux kind

Magnetic force formula and meaning

The law states that if you have a charge, in a magnetic field that is moving then it experiences a force shown as

F = QV (perpendicular) times B

(In the x diagram V in going horizontally and D is going vertically up )

V perpendicular is the side going straight up

The right hand push rule

Motion of charged particles in magnetic field

In the x diagram V

It’ll be going downwards like projectile motion

Work in a circle for this

Fg= Fc

Motor effect meaning and formula

A current-carrying conductor in a magnetic field experiences a force.

Shown as: F = (e)(I perpendicular)(B)

e= length of wire exposed

I = component of current perpendicular to magnetic field

Direction of motor effect hand sign

Making a right angle triangle using this

Magnetic field from A straight wire

Magnetic field strength formula = B = muo times I / 2piR

Theory

• current charging conductors generate magnetic fields around them

• When a current is passed through a straight wire, the magnetic field produced has field lines that form concentric circles around the conductor (circles going anti clockwise around it)

Hand sign for this

Forces by considering superposition of magnetic fields

When a wire carrying electric current is placed in an external magnetic field it will experience a force. This force is called Lorentz force. It arises from the interaction between the wires own magnetic fields around and the external magnetic field

Diagram of this

Meaning of Lorenzt force

Force on a moving charge in electric and/or magnetic fields.

Formula: \vec F = q(\vec E + \vec v \times \vec B)

• \vec F: force on the charge

• q: charge

• \vec E: electric field

• \vec v: velocity of the charge

• \vec B: magnetic field

• \times: vector cross product

Forces between two wires

If they are placed adjacent from each other and they are both parallel then we can consider these two situations

Picture one 1: magnetic field super position; when both wires have currents flowing in the same direction of their magnetic field combine leading to attraction between wire

Picture 2; when the currents flowing opposite directions their magnetic fields counteract resulting in repulsion

Force between two wires formula

Individual wires magnetic field influence (skip for now)

Take for instance, wire A produces a magnetic field that affects wire B. If wire A magnetic field is into the page and wire B locations and wires B current is upwards then the force acts

How does newtons 3rd law applies to situations involving two parallel current carrying conductors

if object A exerts a force onto object B then B will wxert a force on A that is equal in magnitude an direction. This force is the motor effect where current is the wire experiencing the magnetic field B from another current carrying wire

Definition of the ampere

It is defined as the constant current which is maintained in two straight parallel conductors of infinite length of negligible cross sectioned area and placed in a vacuum one metre apart, would produce between these conductors a force equal to 2 × 10^-7 N per unit lengths

Magnetic fields from coils of wire

Middle is North Pole (out of the page)

Outside field is South Pole (into the page)

Right hand rule

North and south mbemonic

north has iut of the page in the middle and into the page on the outside while the south has the opposite

Faradays law of induction

Why is Electromotive Force

It is very similar to voltage even with the same units. It is the push on charges that tend to give rise to currents

Changing flux

Lenz law

The direction of an induced EMF and current in a closed loop opposes the charge in magnetic flux that produces it

Solving problems using lenz law and opposing charges

Conservation of energy here

There is no perpetual motion as lenz law prevents it

To understand Lenz law better read this

How to determine the direction of current through a circuit

Motions EMF(last page of booklet 2)

What is DC

It is direct current in which it is the direct flow of electric charge in one constant direction. So pretty much electrons attract towards the positive plate until the plates are neutralised (v=0). Its graph will look like y= x

What is AC

It is alternating currents so it is a current that periodically reverses direction where voltage oscillates in a wave like pattern. Because of this its graph will look like a sin or cos graph. The energy propagates even through the electrons don’t travel through

How to determine voltage when graphing

Since voltage is also called potential difference so we do positive - negative to find V

What is power and its formula

Power is defined as the rate at which work is done or also the rate at which energy is transformed being measured in watts and Js^-1

P = w/t = change in E / t

Power in electrical circuits formula and meaning

It is when work is done when charges are moved from one plate to the other by W= qv

So

P= qv/t

P= IV

How transformers work

We assume that it’ll have an alternating current because of this it’ll force the north and south poles on both sides of the primary coil to constantly change. Since it is constantly changing the magnetic field will constantly change causing a change in magnetic flux in the secondary coil. Using faradays Law its stating that during this process a emf is present and another way of saying emf is voltage hence due to this we have a current being produced through ohms law and lens law. If the secondary circuit is closed, this induced voltage produces a current (via Ohm’s Law). Lens Law tells us the induced current opposes the change in flux.

The necessity of the use of A.C in Transformers

Transformers require ac because they operate on electromagnetic induction which depends on a changing magnetic flux by faraday’s law

Transformer equations

Vp/vs = Np/Ns = Is/Ip

Pp = ps so VpIp =VsIs soc

Mod 7

What is an electromagnetic wave

Electromagnetic waves are waves of oscillating electric and magnetic fields that travel through space without needing a medium, travelling at the speed of light

What are it’s properties

All waves travel at the same speed

Waves may slow down when travelling through due to refraction

E and B fields mutually sustain each other

EMR would be self propagating

How is are EM wave made

Electromagnetic waves are produced when a changing magnetic field induces an electric field according to Faraday’s Law of Induction.

The changing electric field then induces a magnetic field as described by Ampère–Maxwell Law, allowing continuous propagation.

Gauss’s Law explains that electric fields originate from charges, providing the initial disturbance that generates the wave.

also

Consider an electron oscillating it will accelerate upwards and causing ripples in the E field

Amperes law

This law states that a magnetic field is produced by an electric current or a changing electric field. It explains how time-varying electric fields contribute to magnetic fields, enabling electromagnetic wave propagation.

Gauss law and formula

This law states that the total electric flux through a closed surface is proportional to the net charge enclosed. It shows that electric fields originate from charges and spread outward or inward depending on charge sign.

Formula: electric flux (phi) = q / episole constant

Gauss law and formula for mag

The total magnetic flux through a closed surface is zero. This means magnetic field lines form continuous loops with no isolated magnetic poles.

Mag flux (phi b) = 0

How they link

These laws show a key difference: electric fields have sources (charges), while magnetic fields do not. This explains why in electromagnetic waves, changing electric fields can generate magnetic fields that loop continuously, allowing the wave to propagate.

Unification of elecity and mag

The unification of electricity and magnetism was achieved by James Clerk Maxwell through his set of equations known as Maxwell’s Equations.

These equations showed that electric and magnetic fields are not separate but are interdependent, where changing electric fields produce magnetic fields and vice versa.

This unification led to the prediction of electromagnetic waves, proving that light is an electromagnetic phenomenon.

Formula for velocity and why it is important

V = 1 / sqr mo times eo constant

Shows that E and B fields can exist perpendicular to each other

Electromagnetic spectrum

Refers to the spectrum of different wavelengths of EMR

What do wave lengths tell us

Lower wave lengths equals higher energy

Radio waves

> 1m

It is used for long distance communications

Micro waves

1m - 1mm

Infrared waves

1mm- 700nm

• body temp emits infrarend

• it is used for night vision goggles

Visible

700nm-350nm

ultra violent

350nm-10nm

• causes suntans and sunburns causing the risk of skin cancer

x-ray

10nm - 0.01nm

• use for medical imagery and causes cancer if used mulitple times

Gamma

10pm and onwards

• barely harms body

• 1 of 3 main types of radioactive decay

The Discovery of EM waves (nothing here)

How did maxwell’s equation unfie the dieas of electrictiy and magnatism

Maxwell unified electricity and magnetism by demonstrating that changing electric and magnetic fields generate each other, forming self-propagating electromagnetic waves, thereby proving that light is an electromagnetic phenomenon.

what are his predictions

that changing electric fields produce perpendicular changing magnetic fields which are produced by oscilating a charged particle

from the formula C = 1/ sqr mu times epsile) = speed of light

How are EM waves produced by charge acceleration

When a high voltage alternating potential difference is applied across two terminals, electrons in the conductor oscillate back and forth. This means the charges are constantly accelerating. Since moving charges produce electric fields, an accelerating charge produces a changing electric field. According to Maxwell’s theory, a changing electric field generates a changing magnetic field. These changing electric and magnetic fields sustain each other and propagate outward as an electromagnetic wave at the same frequency as the oscillation.

How do Em waves propagate

Electromagnetic waves propagate through space due to the interaction between changing electric and magnetic fields. When a charge accelerates, it produces a changing electric field. According to the Ampère–Maxwell law, a changing electric field generates a magnetic field. This magnetic field is also changing, and by Faraday’s law of electromagnetic induction (from Michael Faraday), a changing magnetic field induces an electric field.

This continuous process creates a self-sustaining cycle in which electric and magnetic fields regenerate each other. As each new field is produced slightly further from the source, the disturbance propagates outward through space as an electromagnetic wave.

These waves consist of oscillating electric and magnetic fields that are perpendicular to each other and to the direction of propagation, allowing the wave to travel without the need for a medium.

Galileo

Galileo Galilei conducted one of the earliest attempts to measure the speed of light using lanterns placed on distant hills. One observer would uncover a lantern, and the second observer would respond immediately upon seeing the light, allowing Galileo to attempt to measure a time delay. However, no measurable delay was detected, leading to the conclusion that the speed of light is extremely fast. While the experiment lacked accuracy due to limitations such as human reaction time and short distances, it was significant as it challenged the prevailing idea that light travelled instantaneously and initiated scientific investigation into measuring its speed.

Ole Romer

Ole Rømer provided the first quantitative evidence that light has a finite speed through astronomical observations of Jupiter’s moon Io. He observed that the timing of Io’s eclipses appeared delayed when Earth was further from Jupiter and earlier when Earth was closer. Rømer explained this by proposing that light takes time to travel across the increased distance, estimating a speed of approximately 2.2×108 m/s2.2 \times 10^8 \, m/s2.2×108m/s. Although not highly precise, this experiment was significant as it demonstrated that light does not travel instantaneously and established a method of measuring its speed using astronomical distances.

Hippolyte Fizeau

Hippolyte Fizeau conducted the first successful terrestrial measurement of the speed of light using a rotating toothed wheel apparatus. Light was passed through the gaps in the wheel, reflected off a distant mirror, and returned through the wheel. At certain rotation speeds, the returning light was blocked by the teeth, allowing Fizeau to calculate the time taken for the light to travel the known distance. He obtained a value of approximately 3.13×108 m/s3.13 \times 10^8 \, m/s3.13×108m/s. This experiment was significant as it improved accuracy and demonstrated that the speed of light could be measured on Earth using controlled experimental methods.

🔬 Albert A. Michelson

Albert A. Michelson refined the measurement of the speed of light by using rotating mirrors instead of a toothed wheel, significantly increasing precision. By measuring the angular displacement of the reflected light, he was able to calculate the speed of light with high accuracy, obtaining a value close to 3.00×108 m/s3.00 \times 10^8 \, m/s3.00×108m/s. Additionally, in the Michelson–Morley experiment, he attempted to detect the presence of the luminiferous ether using an interferometer. The null result indicated that the speed of light is constant in all directions and that the ether does not exist. This was highly significant as it challenged classical physics and contributed to the development of relativity.

What is Spectroscopy

Spectroscopy is study of interaction between matter and electromagnetic radiation to analyze composition and structure.

flourescent tubes meaning and what is it used for

Fluorescent tubes are glass tubes filled with gas that produce light when electricity passes through. They’re used for lighting in places like schools, offices, and homes because they’re energy-efficient and long-lasting.

How do they work?

• Electric current excites gas (mercury vapour)

• Gas emits ultraviolet radiation

• UV hits phosphor coating inside tube

• Phosphor converts UV into visible light

what is the graph we use for flourescent tubes and what does it mean

intensity vs wavelength diagrams, (y = intensity)

so wavelengths with high relative intensity corresponds to emmited wavelengths and wavelengths with low relative intensity correspond to absorbed wavelengtsh

Incandescent filaments

Incandescent filaments are thin wires, usually tungsten, that glow and produce light when heated by electricity. so pretty much at high temps the electrons gain energy and jump between energy levels so they move chaotically corresponding to emitted wavelengths hence making the emission spectrum look continous (creates many wavelengths)

They’re used in traditional light bulbs for simple, warm lighting but are less energy-efficient.

How do they work?

1. Electric current passes through tungsten filament

2. High resistance causes heating

3. Filament reaches very high temperature

4. Emits visible light (incandescence)

Discharge Tubes

Discharge tubes are gas-filled tubes that emit light when electricity passes through, exciting the gas atoms. So its a type of emission occuring when an electron abosrbs Em radiation of a certain wavelength and emits it at a longer wavelength

They’re used in spectroscopy, neon signs, and identifying elements by their unique emission spectra.

Steps on how discharge tubes work

1. current passes through cold gas

2. excites electrons

3. electrons emit UV radiation

4. Flourescent coating emits visible light through Atoms emit specific wavelengths (line spectrum) when electrons fall back

Why does looking at a diagram for a discharge tube look discontinous?

Because the coating inside the tube is cool and its electrons are only excited by UV radiation from the gas

Reflected sunlight and how does it help us

it’s absorbtion spectrum tell’s us what materials make up its surfaace/atmosphere

How to observe spectra

We have to split up white light into diffection componet wavlengths creating a magnitude of differnet colours.

Absorptions spectrum steps on how it works

1. white light passses through a gas

2. electrons in atoms absorbs specific wavelengths when they have the same energy they are absorb

3. The electrons jump from low to higher energy levels

4. the absorbed waves are gone

How does the Emission Spectrum work

1. Gas is heated or electrically excited causing Electrons to gain energy

2. The electrons jump to higher energy levels

3. They fall back down to lower levels as theyre unstable

4. Releases light as specific colours (wavelengths)

Spectra of Stars (nothing here)