Higher Physics Particles and Waves definitions

Voltage

The energy given to each coulomb of charge that passes through a power supply

Rutherford scattering experiment results

* Most of the alpha particles passed straight through the foil with little or no deflection. Given the foil was at least 100 atoms thick this suggests the atoms must be mostly empty space
* A few particles were deflected through large angles. In order to produce these large deflections, the positively charged alpha particles must be encountering something of very large mass and a positive charge

Antimatter

Consists of particles that are identical to their counterparts in every way apart from charge

What revealed the existence of antimatter

High-energy collisions

Annihilation

When a matter particle meets an anti-matter particle they annihilate, giving off energy

The Standard Model

A model of fundamental particles and interactions

What is the Standard Model a theory of

The Standard Model is our best theory to explain what the Universe is made of. It consists of 17 particles: 12 fermions (6 quarks and 6 leptons) and 5 bosons

Fundamental Particle

A subatomic particle which is not composed of other particles

Fermions

Matter particles. This group contains both quarks and leptons.

6 type of quark

* up (u)
* down (d)
* charm (c)
* strange (s)
* top (t)
* bottom (b)

What are neutrons and protons made up of

quarks

Hadrons

Composite particles which consist of quarks

2 types of hadron

Baryons and mesons

Baryons

Made up of 3 quarks

Mesons

Made up of quark-antiquark pairs

6 Leptons

* electron
* muon
* tau
* electron neutrino
* muon neutrino
* tau neutrino

First evidence for the neutrino

Beta decay

How did beta decay show the evidence of the neutrino

When looking at the reaction it was seen that energy and momentum was not conserved, so this must have been carried away by an unseen particle

4 fundamental forces present when particles interact

* Strong nuclear force
* Weak nuclear force
* Electromagnetic force
* Gravitational force (weakest)

Strong nuclear: Exchange particle & example effect

* Gluon
* Holding protons in nucleus

Weak nuclear: Exchange particle & example effect

* W and Z bosons
* Beta decay

Electromagnetic force: Exchange particle & example effect

* Photon
* Holding electrons in atoms

Gravitational force: Exchange particle & example effect

* Graviton
* Holding matter in planets, stars and galaxies

Bosons

particles associated with the 4 fundamental forces

Electric Field

* A place where there is a force on a charge
* In an electric field a charged particle will experience a force

Electric charge and electric field

Electric charges are surrounded by an electric field

Movement of Charge in an electric field key concept

* Work must be done to move the charge against the direction of force
* The work done in moving the charge against the field = the change in electrical potential energy

Magnetic field wire

A wire with a current flowing through it creates a magnetic field

Stationary charge

A stationary charge creates an electric field

Moving charge

A moving charge creates both an electric field and magnetic field

Acceleration by electric fields

As the particles speed around the beam pipes they enter special accelerating regions where there is a rapidly changing electric field

Deflection by magnetic fields

The protons in the beam pipes would go in a straight line if they were not constantly going past powerful, fixed magnets which cause them to travel in a circle

High energy collisions (particle accelerators)

When they are travelling fast enough they are made to collide within a detector

Fission

A heavy nucleus disintegrates, forming two nuclei of smaller mass number and several free neutrons and energy

Chain reaction

The neutrons released in a fissions reaction go on to cause further fission reactions

2 types of fissions

* Spontaneous fission
* Induced fission

Induced fission

Fission can be induced/persuaded to happen by neutron bombardment

Difficulties with fusion

* Coolant issues
* Containment issues

Coolant issues fusion

* A nuclear fusion reactor generates a lot of heat energy and a safe method is needed to transfer that heat into electricity
* A coolant (usually water) is used to transfer the heat energy

Containment issues fusion

* If plasma comes into contact with the walls of the reactor, it will cool down
* To prevent this from happening, a powerful magnetic field is used to contain the moving charges within the reactor

Irradiance

Irradiance is the power per unit area incident on a surface

Inverse Square Law

Irradiance on a surface will reduce as the distance is increased

Inverse Square Law Experiment

1. Measure the distance (d) between the lamp and the light detector using a metre stick
2. Record the irradiance (I) of the lamp using the light sensor
3. Increase the distance between the lamp and the source and repeat for a further 4 distances
4. Plot a graph with I on the y-axis and 1/d^2 on the x-axis. This will show that irradiance is directly proportional to I/d2

Main variable to ensure constant in inverse square law experiment

Background light level

Wave-particle duality

Light can act both like a wave and like a particle without contradiction. This is known as wave-particle duality

Photoelectric effect

The photoelectric effect is evidence for the particle model of light

Photoemission

Photons of sufficient energy can eject electrons from the surface of materials

When will the photoelectric effect occur

* If the radiation has a high enough frequency
* If the surface is suitable - UV light will not eject electrons from iron, copper or lead but will from sodium and potassium

As irradiance increases how is electron emission affected

The greater the irradiance the more electrons emitted

Current relationship graph with irradiance

Threshold frequency

The minimum frequency of a photon required for photoemission

How is current affected as threshold frequency increases

An increase in frequency will cause an increase in the speed of the electrons being emitted, in turn leading to an increase in current

current threshold frequency graph

Work function

The work function of a material is the minimum energy of a photon required to cause photoemission

Equation for work function

Work function = hfo

Period

The time it takes for one wave to pass a point (s)

Frequency

The number of waves (N) which pass a point in one second (Hz)

Diffraction

The spreading out of waves around obstacles or through a gap

Long wavelength compared to short wavelength diffraction

Long wavelength waves diffract **more** than short wavelength waves

Energy of wave dependent on amplitude

The larger the amplitude the more energy the wave has

Constructive interference

Two sets of waves meet exactly in phase

Destructive interference

Two sets of waves meet completely out of phase

Coherent Sources

Two waves are coherent if they have a constant phase relationship. They will have the same frequency and velocity

Interference of light

Interference can only be explained in terms of wave behaviour and as a result, interference is taken as proof of wave motion

Two sources of coherent light are needed to produce what?

Two sources of coherent light are needed to produce an interference pattern

Zero order (central) maxima

* The waves have zero path difference
* The point they meet is equidistant from each source

Maxima

* Waves arrive in phase
* The waves at the first maxima have a path difference of 1λ
* The waves at the 2nd maxima have a path difference of 2λ

Minima

* Waves arrive out of phase
* The waves at the first minima have a path difference of 1/2λ
* The waves at the 2nd minima have a path difference of 1 1/2λ

Maximum path difference equation

S2P - S1P = mλ

Minimum path difference equation

S2P - S1P = (m + 1/2)λ

Increasing and decreasing separation of maxima

To increase θ, the separation of the maxima, you can:

* increase the wavelength, i.e. move from blue towards red light
* decrease the slit separation, i.e. have more lines per mm

Bohr Model of the Atom

* Electrons exist only in allowed orbits and they do not radiate energy if they stay in this orbit, i.e. Bohr’s model proposed that the classical electromagnetic theory was incorrect
* Electrons tend to occupy the lowest available energy level, i.e. the level closest to the nucleus
* Electrons in different orbits have different energies
* Electrons can only jump between allowed orbits

Bohr Model: How are electrons able to move between levels

* If an electron absorbs a photon of exactly the right energy, it moves up to a higher energy level
* If an electron drops down from a high to a low energy state it emits a photon which carries away the energy

Ground state, E0

The orbit closest to the nucleus

Excited state (E1 - E5 above)

Orbits above the ground state, further away from the nucleus

Ionisation level

The level furthest away from the nucleus - an electron which has gained just enough energy to leave the atom has Ek = 0J

Zero potential energy

Taken to be at infinity (from the nucleus)

Types of spectra

* Continuous Spectra


* Line Emission Spectra
* Line Absorption Spectra

Continuous Spectra

Line Emission Spectra

Line Absorption Spectra

Planck equation relationship

The frequency of the emitted radiation is related to the change in energy ΔE of the electron using the Planck equation

Fraunhofer lines

The absorption lines (Fraunhofer lines) in the spectrum of sunlight provide evidence for the composition of the Sun’s outer atmosphere

Refraction

Refraction is the change in speed and wavelength when a wave moves from one medium into another

Normal (refraction)

An imaginary line at 90\* to the surface, drawn as a dotted line

Incident ray

The ray going towards the surface

Angle of incidence (i)

The angle between the incident ray and the normal

Refracted ray

The ray leaving the surface

Angle of refraction (r)

The angle between the refracted ray and the normal

speed of light as it moves from air to glass

The speed of light decreases as it moves from air to glass

wavelength of light as it moves from air to glass

The wavelength of light decreases as it moves from air to glass

frequency of light as it moves from air to glass

The frequency of light remains the same

Experiment to determine the refractive index of a material

Aim: To determine the refractive index of a medium

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1. Measure angle of incidence θ1 in air and angle of refraction θ2 in the medium using a protractor
2. Gradually increase θ1, measuring pairs of values θ1 and θ2 each time
3. Calculate sinθ1 and sinθ2 for each pair of values
4. Plot a graph with sinθ2 on the x-axis and sinθ1 on the y-axis, this will produce a straight line through zero and the gradient is equal to the refractive index n

Refractive index

The (absolute) refractive index of a medium as the ratio of the speed of light in a vacuum to the speed of light in the medium

Refractive index relational to the frequency of light

As the frequency of light increases, the refractive index increases

Critical Angle

The critical angle is the angle of incidence which produces an angle of refraction of 90\*

Total internal reflection

Total internal reflection occurs when the angle of incidence is greater than the critical angle