Particles And Waves Flashcards
What were Rutherfords observations?
Most particles passed through the gold foil without much deflection.
A few particles were deflected at a larger angle.
What were Rutherford conclusion on the atom?
The atom was mainly empty space.
The centre of the atom was small, highly dense and had a positively charged nucleus.
What are the relative masses, charged and symbols of a proton, neutron and electron.
Proton, mass 1, charge +1, 11p
Neutron, mass 1, charge 0, 10n
Electron, mass 1/1840, charge -1, 0-1e
Order of magnitude
Neutrino
Proton
Hydrogen atom
Dust
Human
Earth
Sun
Solar system
Nearest star
Galaxy
Distance to a quasar
Possible answer for open ended atom question
Rutherford’s experiment on the atom had two main conclusions:
The atom is mainly made up of empty space
At the centre of the atom there was a small, highly dense, positively charged nucleus.
Therefore this diagram could be considered a good representation of an atom.
The centre point (nucleus) is made up of protons (+ve charge) and neutrons (no charge).
The electrons (-ve) are on the outer shells.
The space between the nucleus and electrons would realistically be much greater.
Electrons are thousands of times smaller than protons and neutrons and theretore the scale is not entirely accurate.
What happens when we break al matter down?
Everything is made up of elements, elements are made up of atoms, atoms have a central nucleus, the nucleus has protons and neutrons and further…
What makes protons and neutrons?
They can be broken down into sub atomic particles called fermions which consist of quarks and leptons.
Fermions are a part of the standard model of fundamental particles.
Evidence of sub atomic particles
The existence of of quarks comes from high energy collisions between electrons and nucleons, carried out in particle accelerators. A nucleon is either a proton or neutron, which are made of quarks.
What is the standard model of fundamental particles?
Physicists have developed a theory called the standard model which explains what the world is and what holds it together.
It is a simple and comprehensive theory that explains all hundreds of the particles and complex interactions with only:
6 quarks
6 leptons (best known lepton is an electron)
Force carried particles (like a photon, known as a boson)
When all fermions interact with each other by exchanging force carried particles.
What is antimatter?
For every type of matter particle, a corresponding antimatter particle exists, or antiparticle.
They look and behave just like the corresponding matter particle, except they have opposite charges.
What’s annihilation?
Matter and antimatter cannot coexist close to each other. When these collide, they disappear releasing energy, which is evidence of the existence of antimatter.
What are fermions?
The fermions (quarks and leptons) are split into their particles and anti particles.
The 6 quarks
Up and Down
Strange and Charm
Top and Bottom
The 6 leptons
Electron and electron neutrino
Muon and muon neutrino
Tau and tau neutrino
What holds all the particles together, allows them to interact?
The electromagnetic force
Strong nuclear force
Weak nuclear force
Gravity
What are force mediating particles - bosons?
They describe the way in which the particles interact with each other.
Photons (electromagnetic force)
W and Z bosons (weak force)
Gluon (strong force)
The electromagnetic force
This force causes like charged things to repel and oppositely charged things to attract.
Many everyday faces, such as friction and magnetism are caused by the EM force.
For instance, the force that keeps you from falling through the floor is the electromagnetic force which causes the atoms making up the matter in your feet and the floor to resist being displaced. The carrier particle is the electromagnetic force is photon(v)
The strong nuclear force
What binds the nucleus together.
The nucleus of the atom consists of a bunch of protons and neutrons crammed together. Since neutrons have no charge and the positively charged protons repel one another, but why does the nucleus not blow apart?
The strong nuclear force holds them together to form hadrons, the carrier particles are called gluons.
The strong nuclear force acts inside the nucleus to keep the protons from flying apart.
The EM force (like charged repel) means that protons should repel each other.
The nuclear force acts against the electromagnetic force and they balance each other out. This allows the protons to stay inside the nucleus. The gluon force works in a range of approximately x10^-14.
The weak nuclear force
There are six kinds of quarks and six types of leptons. But all the stable matter of the universe appears to be made of just the two least massive quarks (up and down), the least massive charged lepton (the electron) and the neutrinos.
Weak interactions are responsible for the decay of massive quarks and leptons into lighter quarks and leptons.
The carrier particles of the weak interactions are the W+, W-, and the Z particles. The Ws are electrically charted and the Z is neutral.
Summary of force carrier particles - bosons
Gluon, strong, holds nucleus together.
W and Z, weak, fermion decay
Photon, electromagnetic, causes like charges to repel and opposite charges to attract.
Fermions ( mass particles) symbols and boson symbols.
See picture
What are hadrons?
They are made up of baryons which are made of 3 quarks and mesons which are made up for 2 quarks (a quark and an antiquark - quark pair)
Quarks have fractional charged so combine to give hadrons with an overall charge.
What is Beta decay?
Beta decay (symbol) is a type
Of radioactive decay in which a neutron is transformed into a proton (or vice versa) inside an atomic nucleus.
As a result the nucleus emits a detectable beta particle - which is an electron or anti electron (positron)
Beta decay is mediated by the weak force.
BETA DECAY PRODUCES A PROTON, AN ELECTRON AND AN ANTINEUTRINO.
It is the first evidence of the neutrino.
(See equation)
What are neutrinos?
Neutrinos were discovered during the study of beta decay. The law of conservation of momentum was not being observed by the particles.
( see diagram)
Momentum before and after the decay did not match up do the hypothesis was that another particle which could be be seen, must be moving right. It was named the neutrino and has a very small mass and weak interaction with other particles.
What is an electric field?
In an electric field, a charge experiences a force.
Electric field lines show the direction of a force (on a positive charge).
The separation of the field lines gives an indication of the strength of the field.
Field strength decreases with distance.
A uniform electrode field exists between two parallel charged plates. The space around an electrics charge where the influence of that charge on another charge can be detected, is called an electric field.
Like charges repel and unlike charged attract.
Field lines are continuous, starting on a +ve charge and ending on a -ve charge. They give the direction of the force acting on a positive charge at a point in the field.
How is a potential difference produced through two points in an electrode field?
When a charge Q is moved in an electrode field, work W is done. If one joule of work is done moving one coulomb of charge between two points in an electrode field, the potential difference between the two points is 1 volt.
The potential difference between two points in an electric field is a measure of the world done in moving one coulomb of charge between two points.
V = W/Q
Relationship between v and g
Change in electrical potential energy = electric force x
distance
If a force is in direction of electric field, energy appears as kinetic energy.
If force is against the direction of the electric field, energy is stored as potential energy.
QV = 1/2mv^2
What happens if you change the distance of the field when using formula QV = 1/2mv^2?
This would not affect the velocity of the charge as it is only dependant on the variables in the equation - Q, V and m. These have not changed so neither does the velocity.
What happens if you change the charge of the particle when using the formula QV=1/2mv^2?
This would affect the velocity of the charge. A smaller Q means smaller velocity and a larger Q means larger velocity.
What happens when an electrode field is applied to a conductor?
The free electric charges in the conductor move.
How do electricity and magnetism interact?
When a charged particle moved, a magnetic field is generated. A current carrying wire will have a magnetic field behind it
What direction does the magnetic field do when a switch is open, closed or the electron flow is reversed?
Open: when the switch is open, no current flows, and the compasses point (magnetic field) point north.
Closed: the needles in the compass (magnetic fields) move in a circular direction. When the electron flow is reversed, the magnetic field also changes direction.
Left hand grip rule
The thumb represents the direction of current flow, the (hand to fingers) represents the magnetic field direction.
Right hand grip rule
Used for conventional current (positive charge flowing to negative)
What would happen when a moving electric charge is brought into a static magnetic field?
The moving electric charge is surrounded by an (electro) magnetic field. This interacts with the static magnetic field which causes the charge to experience a force.
Flemings left hand rule
Protons +ve (conventional current)
The current, field and motion of force are all perpendicular to each other.
Current - Central finger
Field - Fore finger
Motion of force - thuMb
Flemings right hand rule
Electrons -ve
The current field and motion of force are all perpendicular to one another.
Current - Central finger
Field - Fore finger
Motion of force - thuMb
What does an X and a O stand for in magnetic fields?
X - magnetic field is going into the page.
O - magnetic field is coming out of the page.
Evidence of particle deflection
• The Sun produces a solar wind a flow of charged particles) which can cause significant damage to life and electrical equipment.
• The power of the solar wind can fluctuate over time.
• Fortunately for us, Earth has a strong magnetic field (North and South poles) that interact with these charged particles.
• The force produced by the magnetic field on the particles deflect them to the poles.
• This is why Aurora (Northern and Southern lights) are produced.
What are hydrogen and helium atoms made of?
Hydrogen atoms contain one proton in their nucleus and one electron.
Helium atoms contain two protons and two electrons.
What is the atomic number?
It’s the number of protons in the nucleus (Z) and also equal to the number of orbiting electrons.
What’s the mass number?
The total number of protons and neutrons (A), known as the nucleons.
What’s the symbol for the chemical element?
X
How does the atom have no overall charge?
Because the number of protons and electrons are equal.
What are elements arranged in on the periodic table?
An increasing order of atomic number.
What is radioactive decay?
Many nuclei are unstable. In order to achieve stability, they can emit nuclear radiation in the form of alpha, beta or gamma.
Such unstable nuclei are called radioisotopes or radionuclides.
The process of emitting radiation is called decay.
What are the three main types of radiation, and their nature, and symbol?
Alpha particle, helium nucleus, 42He, a
Beta particle, fast electron, 0-1e, B
Gamma ray, high frequency EM wave, Y
Radioactive decay in alpha, beta and gamma.
In alpha decay, the mass number loses 4 and the atomic number loses 2.
In beta decay, the mass number remains the same and the atomic number gains 1.
In gamma decay, there is no change in the isotope and only energy is emitted.
What is a resulting isotope?
It’s known as the daughter isotope and is a different element, after the element has gone through radioactive decay. It is the product of radioactive decay.
To find the number of electrons in a nucleus of an isotope…
Divide the mass number by the number of protons
What is nuclear fission?
Fission occurs when a heavy (large mass number) nucleus splits up into two lighter nuclei (smaller mass number) and several neutrons.
Energy is released during fission.
Fission may be spontaneous or induced.
The heavy nucleus - Uranium-235 (uranium atom)
What is induced fission?
When a large, heavy nucleus is bombarded by neutrons.
What is spontaneous fission?
It occurs without any outside influence.
What is nuclear fusion?
A fusion reaction is one where two small nuclei join together to form a heavier nucleus.
What does E=mc^2 find and how does it work?
It finds the energy released during fission.
The missing mass is exactly proportional to the energy produced by the reaction.
You find the total mass before and after, find the difference which is equal to c.
True or false: Induced nuclear fission will show a neutron being added on in the equation.
True
True or false: two hydrogen isotopes will be shown when fusion occurs as two lighter nuclei join together.
True
What does nuclear fusion require to occur?
Large amounts of heat.
It is the process of fusion which produces energy realised by the sun and stars.
Uses for nuclear fission.
Current nuclear reactors use nuclear fission to generate power. In nuclear fission, you get energy from splitting one atom into two atoms. In a conventional nuclear reactor, high-energy neutrons split heavy atoms of uranium, yielding large amounts of energy, radiation and radioactive wastes that last for long periods of time
Uses for nuclear fusion.
In nuclear fusion, you get energy when two atoms join together to form one. In a fusion reactor, hydrogen atoms come together to form helium atoms, neutrons and vast amounts of energy. It’s the same type of reaction that powers hydrogen bombs and the sun. This would be a cleaner, safer, more efficient and more abundant source of power than nuclear fission.
Problems with fusion.
Scientists are working on developing a practical fusion reactor.
To achieve fusion, scientists heat the hydrogen isotopes deuterium and tritium to at least 100 million degrees Celsius. This strips electrons from the isotopes, creating a plasma of bare nuclei.
The problem is that the plasma produced during the fusion reaction is at a temperature of around 100 million degrees Celsius.
This would vaporise any material it came into contact with.
If this plasma is hot and dense enough, the two types of nuclei fuse, giving off neutrons and huge amounts of energy.
However, the plasma can only be contained by strong magnetic fields, and creating containment fields that do not leak has proved very difficult.
What is more, no one has managed to generate a stable fusion reaction that passes the “break-even” point, where the reaction is generating more energy than it takes to sustain it.
The largest fusion device in Europe is at Culham in Oxfordshire, it is the JET [Joint European Torus].
A torus is a doughnut shape.
What do light waves carry?
Energy
What is the photoelectric effect?
When might falls on certain substances, energy is absorbed and if there is sufficient energy, electrons may be ejected from the atoms of the substance.
Photoelectric effect experiment
See notes
Photoelectric effect experiment description
The glass tube is evacuated
Light can be shown onto the glass plate through the window. Any electrons ejected from zinc atoms will be attracted to the anode. A current will be observed on the ammeter.
A current is observed when UV is selected but not when visible light is shone onto the zinc plate. We can deduce that only UV has enough ENERGY to eject electons from the zinc atoms.
This cannot be explained by wave theory of light. If light is a wave then energy is being continuously supplied. Any colour should eventually supply enough energy to eject an electron. This does not happen no matter how bright the light may be.
We must conclude that the energy comes in short bursts or packets and is transferred to the electron on an ‘all or nothing’ basis. Either each packet has enough energy to eject an electron, or it doesn’t. UV packets have enough energy, visible light packets do not.
During this experiment we are observing light behaving as a stream of particles.
These packets or particles of light are called PHOTONS. Photons of UV have enough energy to eject electrons, photons of visible light don’t.
Gold leaf electroscope
See notes
Summary of photoelectric effect.
Sometimes when electromagnetic radiation above a certain frequency strikes a surface, electrons are emitted.
This can be used to detect radiation and is the basis on which solar cells and light dependant resistors operate.
What is threshold frequency?
F0, below a certain frequency, there is no photoelectric emission, which is known as the the threshold frequency.
What is irradiance?
The power per unit area
Increasing irradiance at f<f0 will have no effect.
Increasing irradiance at f>f0 will cause more photoelectric emission. They are directly proportional.
A bigger irradiance results in a bigger photoelectric current produced.
What is quantum theory - does light travel in waves or photons?
If we increase irradiance at frequencies above fo will cause more photoelectric emission.
But wave theory of light disagrees with this as the waves are continuous ie., don’t change.
It was suggested by scientist Max Planck in 1905 that light doesn’t travel as a continuous wave but travels in packets called photons.
Modern physics now takes the view that light can act both like a wave and like a particle without contradiction. It depends on how we test it.
If we look for evidence that it is a wave, we can find it. But also, if we look for evidence that it is a particle we can find that too. The universe seems to be made up of things that are both particle-like and wave-like. This is known as wave-particle duality.
To eject an electron from a metal requires a precise amount of energy. A weak UV source has sufficient energy to do this for a clean zinc surface, but no matter how high the irradiance of the white light is, no electrons are ejected.
This is true even though, over a period of time, the total energy of the white light is greater than that of the UV.
In 1904 Einstein applied an earlier idea of Planck to the phenomenon and proposed that light was not a continuous wave, but existed as a stream of ‘packets’ or ‘quanta’
These quanta are called photons and are particles of light (and other electromagnetic radiation), although unlike other particles they have no mass.
What is the energy of photons formula?
E =hf
What is the formula combined from v=flambda and E=hf, to find the energy?
E=hc/lambda
What formula can be used to find the irradiance of photons when more photons are provided by an intense beam of light?
I = Nhf
I irradiance.
N number of photons per second per square meter.
f frequency
h plancks constant
What is the work function?
When a photon is absorbed its energy it used to release an electron.
The minimum energy needed by an electron to proved photoelectric emission (escape from a metal) is called the work function, which is dependant on frequency.
W = hf0
Every metal has a different value of work function.
Threshold frequency and work function summary.
The threshold frequency, f0, is the minimum frequency of a photon required for photoemission.
The work function, E0, of a material is the minimum energy of a photon required to cause photoemission.
Formula for extra kinetic energy when using the work function and the threshold frequency.
Such an electron would escape but have no kinetic energy.
If the energy of the incoming electron.
E=hf (where f>f0) is greater than the work function. Then the extra energy will appear as kinetic energy.
Ek = E - E0
Ek = hf- hf0
Problem solving points when solving with irradiance and current.
Is irradiance increases, so does the number of photons per second per square meter.
Therefore there is more photoelectric emission.
This means that current ( flow of electrons) also increases.
See notes for graph.
Experiment for refractive index of a Perspex block.
See notes
What’s the difference between sin1 and sin2, and what is their relationship?
The ratio of sin1/sin2 is constant when light passes obliquely from medium 1 to medium 2.
Sin1 is in a vacuum (or air) and sin2 is in the medium.
What is the refractive index in air and what does this do to the formula?
It is 1.
We can say n2/n1 = sin1/sin2
What is the refractive index?
The refractive index measures the effect a medium has on light. The greater the refractive index, the greater the change in speed and direction.
The absoloute refractive index is always a value greater than or equal to 1.
How do you calculate n from a graph of sin1/sin2?
The gradient.
Refractive index is in relationship to frequency. (and colours)
Different colours are refracted through different angles.
The refractive index depends on the frequency (colour) of the incident light.
The refractive index of the medium for blue light is greater than that for red.
This is why when white light passes through a triangular prism, it is broken up into a spectrum.
What is changed and unchanged during refraction?
Wavelength and velocity change during refraction, but frequency of a wave is unaltered by a change in medium.
Experiment to find the critical angle.
See notes
When light is refracted, when light is at the critical angle? When light shows total internal reflection.
The ray of light will leave the block.
The ray of light is refracted at 90^ which is the critical angle.
The ray of light is at a larger angle than the critical angle and is refracted inside the block.
What is the symbol for the critical angle?
Thetac
What is the critical angle?
It’s the angle of incidence when the angle of refraction is 90^.
It is the smallest angle of incidence above which total internal reflection occurs.
What is total internal reflection?
It takes place when all of a light ray is completely reflected and none of it is refracted.
This takes place at angles above the critical angle.
Why is a curved, semi circular block used to find the critical angle?
Because there is no change of direction at the curved surface because the radial array strikes the surface at normal incidence.
Uses of total internal reflection.
It can be used to send light signals along optical fibres.
This can be used to send telecommunications such as internet, TV and phone.
What is the period of a wave?
It is the time take for one complete wave to pass a point (s).
What is the frequency of a wave?
Is is the number of waves to pass a point in one second (Hz).
What is the energy of a wave dependant on?
It’s amplitude (a).
What does it mean when two waves are in phase?
The he maximum and minimum points on the wave occur at the same time.
What does it mean if two waves are completely out of phase?
The maximum of one wave occurs at the minimum of the other.
What is coherent light?
If two waves coming from two sources have the same frequency, wavelength and velocity and are in phase, then the two sources are coherent. They will also have the same amplitude.
Coherent light is light which has no phase difference.
What is the law of reflection?
When a wave is reflected off of a surface, the angle of incidence is equal to the angle of reflection.
What are the rules of refraction
Waves change speed when passing from one medium to another.
The direction also changes when the incident ray is not on the normal.
What are the rules of diffraction?
Waves spread out around corners.
When passing through the gap the waves appear to curve if the gap is similiar to the wavelength.
What is the interference?
When two sets of waves meet, they combine to produce a new pattern.
The new pattern depends on the original wavelengths, amplitudes etc.
Waves combine in either of two ways:
- constructive interference
- destructive interference
Interference is the test for a wave.
What is constructive interference?
When two sets of waves meet in phase. Two crests meet or two troughs meet to produce a larger crest or trough.
What is destructive interference?
When two waves meet completely out of phase (180^ out of phase).
A crest meets a trough and combine to cancel each other out and produce no wave at that point.
Note that if waves are not of equal amplitude, then complete cancelling out doesn’t occur.
What is path difference?
An interference pattern is more easily explained in terms of path difference.
If the two waves train equal distances, (eg AC=BC), then there is no path difference.
If the two waves train different distances, there is a path difference.
What is the maxima?
In an interference pattern formed by two coherent sources, maxima occurs at points of constructive interference.
Path difference = mlambda
(Where m is an integer)
The space between each maxima is equal to one wavelength.
What is the minima?
It occurs at points of destructive interference.
Path difference = (m+1/2) lambda
Interference of sound
Loudness of the sound varies as it is moved across the loudspeakers
Loud - maxima - constructive interference
Quiet - minima - destructive interference
When the microphone is midway between the loudspeakers, the path difference is 0 (central path)
Double slit relationships
See notes
What is a grating and monochromatic light and how do they relate?
A grating consists of many equally spaced slits positioned extremely close together (Eg 300 lines per mm).
Light is diffracted through each slit and interference takes place in a similiar fashion to the double slit.
The advantage of grating is that much more light is transmitted through and a clearer interference pattern is seen.
Monochromatic light is light which consists of a single wavelength or frequency. - all photons have the same energy.
When monochromatic light is passed through a grating, maxima are observed on either side of a central maximum.m
It can be seen that for blue light the maxima is closer to the central maximum than red light.
How does grating produce a spectra?
A central white maximum is produced. All wavelengths interfere constructively at this point.
Spectra are produced on either side of the central white maximum.
The red part of each spectrum is furthest away from the central maximum.
The second order spectra are more spread out than the first order spectra. This order spectra overlaps the second order spectra.
What needs to be in the same units when using the grating equation?
d and lambda
d is the distance between the slits on the grating. It is ussually very small and can be found by doing 1/ the number of slits/ lines (N) per METER on the grating.
How do you increase theta (the separation of the maxima)?
Increase the wavelength (move from blue towards red light).
Decrease the slit seperation ( have more lines per mm)
Move the screen further away.
Comparing spectra from prisms and gratings
Prisms
One Spectrum
Red light is deviated the least, violet is deviated the most
Prism forms a spectrum by refraction.
Gratings
A number of Spectra on either side of the central white maximum
Red light is further away from the central maximum, violet light is closer.
The second order spectra are more spread out than the first order spectra. The third order spectra overlap the second order spectra.
The grating produces a spectra by the interference of light which is diffracted as it passes through the many slits on the grating.
Why is it necessary to use magnetic fields to contain plasma?
Plasma would cool down if it came to close to the sides of the reactor (reaction would stop)
Reactions require a very high temperature so plasma could melt the sides of the reactor.
Why is an alternating supply used in a linear accelerator?
Particles always accelerate in the same direction (forwards).
Force on particles is always in the same direction.
Differences in magnetic fields???
Opposite directions.
Stronger fields.
Example Answer about electrons hitting a glowing surface and the surface increasing brightness 6????
Screen will be brighter, electrons will gain more energy and move faster.
Why do lengths of tubes increase along a particle accelerator?
Alternating voltage has a constant frequency rather than a frequency that changes.
As the speed of a proton increases, they travel further in the same direction.
Comparing orders of magnitude questions:
Divide them, how many x10s
Why are the proton and neutron not fundamental particles?
They ate composed particles, fundamental particles are composed.
How is this statement correct: all baryons are hadrons, but not all hadrons are baryons.
Baryons are hadrons as they are composed of three quarks.
Mesons/ some hadrons are made from a quark- antiquark pair so are not baryons.
Why are leptons and quarks not known as fundamental particles?
Because they can’t be subdivided.
Why can the gluon not be the force mediating particle for the gravitational force?
Because the strong force (gluons) have a short range.
The gravitational force requires infinite range.
Define the term fundamental particles
They cannot be composed of other particles.
What is a meson made of?
An anti quark pair.
Why can energy be released in a fusion reaction?
Because mass is converted into energy.
Define the term irradiance
The power incident per unit area
When doing a light experiment, why may it be covered up?
To prevent reflections.
Why may photoelectric not be ejected from a surface?
If the UV of the light is not high enough.
If the frequency of the UV light is less than the threshold frequency.
How are dark lines of sunlight produced in a spectra?
Photons of some energies/frequencies are absorbed in the suns outer atmosphere
Why may the potion of lines be different in different spectra’s of galaxies?
Light is redshifted towards red as galaxies are moving away from the sun.
What are three features of the Bhor model of the atom?
A central positively charged nucleus.
Negatively charged electrons in discrete energy levels orbiting the nucleus, not radiating energy.
Each line in a spectrum is produce when an electron moves from one energy level to another.
Why is a spectrum produced in a glass prisim?
Different frequencies/ colours have different refractive index.
They are also refracted through different angles.
What is one difference in the spectrum produced by a lower refractive index glass to a higher one?
Less deviation in the spectrum positioning.
How does a greater refractive index cause more sparkles in the material?
Because the critical angle is smaller, and total internal reflection is more likely with the more refractive material.
What is meant by the term ‘critical angle’?
The angle of incidence when the angle of refraction is 90^.
Why may the lengths of a tube be increased when an alternating voltage is used in a particle accelerator?
As the speed of the particle increases, they travel further in the same time.
Why are protons accelerated by an electric field?
Because they are positively charged and experience a force in an electric field.
How is a minimum formed in an interference pattern?
Waves meet completely out of phase.
What is meant by the term coherent?
The waves fork the two sources have a constant phase relationship and have the same frequency/wavelength and velocity.
How is a maximum produced in interference?
When waves meet exactly in phase.
If the distance between two gaps is increased in path different experiments, what will happen to the . Order maximum?
The path difference stays the same because the wavelength has not changed.
What is the path different dependant on?
The wavelength - shorted wavelength, smaller path didference, sinO is proportional to lambda.
Why might bright fringes be produced by waves meeting in phase?
Because the waves meet exactly in phase.
Question 8b 2022
True or false: If the refractive index of a medium is the same as the refractive index, there is no refraction or change in speed/wavelength/direction.
True
What is irradiance?
When radiation falls on a surface, the irradiance is defined as the power per unit area. It can also be referred to as intensity.
What is the units of irradiance?
Wm^-2
Experiment to prove the inverse square law.
See flashcards
What is the relationship between irradiance and distance? (Experiment)
Measure irradiance levels at different distances and plot a graph of your results.
As you move further away from a point source, the irradiance of radiation decreases. The relationship between irradiance and distance can be shown as inverse square law
I = k/d^2
Or other formula on sheet.
What is an emission spectra?
The emission spectra is a range of colours given out by a light source.
Continuous spectra - given by white light passing through a prism.
Line spectra - some sources of light such as sodium and mercury vapour lamps do not produced continuous spectra when views through a spectroscope. They produce line spectra - coloured lines spread out by different amounts.
What is the explanation of the emission spectra in relation to the Bhor model?
The electrons have different fixed energies in different orbits.
They can move between each levels but cannot stop between them.
Explanation of energy level diagrams
In the smallest orbit, E0, the electron has least energy and is said to be the ground state (negative).
An electron which moves to a higher energy level is said to be in an excited state.
If an electron gains enough energy it can reach the top level, the ionisation level (zero potential)
If it is here, the electron can leave the atom.
If the energy levels is denoted as triangles, then the frequency of the emitted photon will be expressed as (formula)
The frequency of the emitted photon is therefore determined by the magnitude of the energy change.
Frequencies of between 4-7x10^14 are in the visible spectrum.
Emitted photons between these frequencies are the colours shown on spectra lines.
What is an emission line?
An emission line in a spectrum occurs when an electron makes a transition between an excited energy level such as E2 to a lower energy level such as E1.
The emission line will appear brighter if more electrons make that particular transition.
What is an absorption line?
It’s a line in a spectrum that occurs when an electron in energy levels E1 absorbs radiation of energy hf and is excited up to energy level E2.
Relationship between frequency and wavelength - spectra.
F and E are proportional.
The bigger the E2 - E1, the bigger the frequency.
Using v = flambda (as v is a constant) we can deduce that the bigger the f the smaller the lambda.
In other words, when traingleE goes up, frequency goes up and wavelength goes down.
What is continuous spectra produced from?
Solids, liquids and high pressure gasses.
What is line spectra produced from?
Low pressure gasses.
What is the number of energy levels equivalent too?
The number of possible transmissions from a higher to a lower level.
What is the absorption spectrum?
It is a spectrum of an element which consists of black lines on a continuous spectrum.
The lines are in exactly the same postings as the bright lines in the emission spectrum.
Absorption lines in the sun
Absorption lines occur in the suns spectrum because of the gasses present in the outer part absorb light of particular frequencied.
The white light is produced in the centre of the sun but after passing through the layer of gas, some frequencies are missing.
This gives dark lines and allows elements which make up the sun to be determined.
The dark lines are called Fraunhofer lines.
Baryons
Composed of three quarks
Emission line PowerPoint and path difference PowerPoint
Check
Emission and absorption diagrams
See notes
