Particles And Waves

Question 1

What were Rutherfords observations?

Answer 1

Most particles passed through the gold foil without much deflection.

A few particles were deflected at a larger angle.

Question 2

What were Rutherford conclusion on the atom?

Answer 2

The atom was mainly empty space.

The centre of the atom was small, highly dense and had a positively charged nucleus.

Question 3

What are the relative masses, charged and symbols of a proton, neutron and electron.

Answer 3

Proton, mass 1, charge +1, 11p

Neutron, mass 1, charge 0, 10n

Electron, mass 1/1840, charge -1, 0-1e

Question 4

Order of magnitude

Answer 4

Neutrino
Proton
Hydrogen atom
Dust
Human
Earth
Sun
Solar system
Nearest star
Galaxy
Distance to a quasar

Question 5

Possible answer for open ended atom question

Answer 5

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.

Question 6

What happens when we break al matter down?

Answer 6

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…

Question 7

What makes protons and neutrons?

Answer 7

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.

Question 8

Evidence of sub atomic particles

Answer 8

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.

Question 9

What is the standard model of fundamental particles?

Answer 9

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.

Question 10

What is antimatter?

Answer 10

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.

Question 11

What’s annihilation?

Answer 11

Matter and antimatter cannot coexist close to each other. When these collide, they disappear releasing energy, which is evidence of the existence of antimatter.

Question 12

What are fermions?

Answer 12

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

Question 13

What holds all the particles together, allows them to interact?

Answer 13

The electromagnetic force

Strong nuclear force

Weak nuclear force

Gravity

Question 14

What are force mediating particles - bosons?

Answer 14

They describe the way in which the particles interact with each other.

Photons (electromagnetic force)
W and Z bosons (weak force)
Gluon (strong force)

Question 15

The electromagnetic force

Answer 15

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)

Question 16

The strong nuclear force

Answer 16

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.

Question 17

The weak nuclear force

Answer 17

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.

Question 18

Summary of force carrier particles - bosons

Answer 18

Gluon, strong, holds nucleus together.

W and Z, weak, fermion decay

Photon, electromagnetic, causes like charges to repel and opposite charges to attract.

Question 19

Fermions ( mass particles) symbols and boson symbols.

Answer 19

See picture

Question 20

What are hadrons?

Answer 20

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.

Question 21

What is Beta decay?

Answer 21

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)

Question 22

What are neutrinos?

Answer 22

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.

Question 23

What is an electric field?

Answer 23

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.

Question 24

How is a potential difference produced through two points in an electrode field?

Answer 24

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

Question 25

Relationship between v and g

Answer 25

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

Question 26

What happens if you change the distance of the field when using formula QV = 1/2mv^2?

Answer 26

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.

Question 27

What happens if you change the charge of the particle when using the formula QV=1/2mv^2?

Answer 27

This would affect the velocity of the charge. A smaller Q means smaller velocity and a larger Q means larger velocity.

Question 28

What happens when an electrode field is applied to a conductor?

Answer 28

The free electric charges in the conductor move.

Question 29

How do electricity and magnetism interact?

Answer 29

When a charged particle moved, a magnetic field is generated. A current carrying wire will have a magnetic field behind it

Question 30

What direction does the magnetic field do when a switch is open, closed or the electron flow is reversed?

Answer 30

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.

Question 31

Left hand grip rule

Answer 31

The thumb represents the direction of current flow, the (hand to fingers) represents the magnetic field direction.

Question 32

Right hand grip rule

Answer 32

Used for conventional current (positive charge flowing to negative)

Question 33

What would happen when a moving electric charge is brought into a static magnetic field?

Answer 33

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.

Question 34

Flemings left hand rule

Answer 34

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

Question 35

Flemings right hand rule

Answer 35

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

Question 36

What does an X and a O stand for in magnetic fields?

Answer 36

X - magnetic field is going into the page. O - magnetic field is coming out of the page.

Question 37

Evidence of particle deflection

Answer 37

• 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.

Question 38

What are hydrogen and helium atoms made of?

Answer 38

Hydrogen atoms contain one proton in their nucleus and one electron. Helium atoms contain two protons and two electrons.

Question 39

What is the atomic number?

Answer 39

It’s the number of protons in the nucleus (Z) and also equal to the number of orbiting electrons.

Question 40

What’s the mass number?

Answer 40

The total number of protons and neutrons (A), known as the nucleons.

Question 41

What’s the symbol for the chemical element?

Answer 41

X

Question 42

How does the atom have no overall charge?

Answer 42

Because the number of protons and electrons are equal.

Question 43

What are elements arranged in on the periodic table?

Answer 43

An increasing order of atomic number.

Question 44

What is radioactive decay?

Answer 44

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.

Question 45

What are the three main types of radiation, and their nature, and symbol?

Answer 45

Alpha particle, helium nucleus, 42He, a Beta particle, fast electron, 0-1e, B Gamma ray, high frequency EM wave, Y

Question 46

Radioactive decay in alpha, beta and gamma.

Answer 46

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.

Question 47

What is a resulting isotope?

Answer 47

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.

Question 48

To find the number of electrons in a nucleus of an isotope…

Answer 48

Divide the mass number by the number of protons

Question 49

What is nuclear fission?

Answer 49

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)

Question 50

What is induced fission?

Answer 50

When a large, heavy nucleus is bombarded by neutrons.

Question 51

What is spontaneous fission?

Answer 51

It occurs without any outside influence.

Question 52

What is nuclear fusion?

Answer 52

A fusion reaction is one where two small nuclei join together to form a heavier nucleus.

Question 53

What does E=mc^2 find and how does it work?

Answer 53

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.

Question 54

True or false: Induced nuclear fission will show a neutron being added on in the equation.

Answer 54

True

Question 55

True or false: two hydrogen isotopes will be shown when fusion occurs as two lighter nuclei join together.

Answer 55

True

Question 56

What does nuclear fusion require to occur?

Answer 56

Large amounts of heat. It is the process of fusion which produces energy realised by the sun and stars.

Question 57

Uses for nuclear fission.

Answer 57

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

Question 58

Uses for nuclear fusion.

Answer 58

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.

Question 59

Problems with fusion.

Answer 59

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.

Question 60

What do light waves carry?

Answer 60

Energy

Question 61

What is the photoelectric effect?

Answer 61

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.

Question 62

What is threshold frequency?

Answer 62

F0, below a certain frequency, there is no photoelectric emission, which is known as the the threshold frequency.

Question 63

What is irradiance?

Answer 63

The power per unit area Increasing irradiance at ff0 will cause more photoelectric emission. They are directly proportional. A bigger irradiance results in a bigger photoelectric current produced.

Question 64

What is the energy of photons formula?

Answer 64

E =hf

Question 65

What is the formula combined from v=flambda and E=hf, to find the energy?

Answer 65

E=hc/lambda

Question 66

What formula can be used to find the irradiance of photons when more photons are provided by an intense beam of light?

Answer 66

I = Nhf I irradiance. N number of photons per second per square meter. f frequency h plancks constant

Question 67

What is the work function?

Answer 67

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.

Question 68

Threshold frequency and work function summary.

Answer 68

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.

Question 69

Formula for extra kinetic energy when using the work function and the threshold frequency.

Answer 69

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

Question 70

Problem solving points when solving with irradiance and current.

Answer 70

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.

Question 71

What’s the difference between sin1 and sin2, and what is their relationship?

Answer 71

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.

Question 72

What is the refractive index in air and what does this do to the formula?

Answer 72

It is 1. We can say n2/n1 = sin1/sin2

Question 73

What is the refractive index?

Answer 73

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.

Question 74

How do you calculate n from a graph of sin1/sin2?

Answer 74

The gradient.

Question 75

Refractive index is in relationship to frequency. (and colours)

Answer 75

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.

Question 76

What is changed and unchanged during refraction?

Answer 76

Wavelength and velocity change during refraction, but frequency of a wave is unaltered by a change in medium.

Question 77

When light is refracted, when light is at the critical angle? When light shows total internal reflection.

Answer 77

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.

Question 78

What is the symbol for the critical angle?

Answer 78

Thetac

Question 79

What is the critical angle?

Answer 79

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.

Question 80

What is total internal reflection?

Answer 80

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.

Question 81

Why is a curved, semi circular block used to find the critical angle?

Answer 81

Because there is no change of direction at the curved surface because the radial array strikes the surface at normal incidence.

Question 82

Uses of total internal reflection.

Answer 82

It can be used to send light signals along optical fibres. This can be used to send telecommunications such as internet, TV and phone.

Question 83

What is the period of a wave?

Answer 83

It is the time take for one complete wave to pass a point (s).

Question 84

What is the frequency of a wave?

Answer 84

Is is the number of waves to pass a point in one second (Hz).

Question 85

What is the energy of a wave dependant on?

Answer 85

It’s amplitude (a).

Question 86

What does it mean when two waves are in phase?

Answer 86

The he maximum and minimum points on the wave occur at the same time.

Question 87

What does it mean if two waves are completely out of phase?

Answer 87

The maximum of one wave occurs at the minimum of the other.

Question 88

What is coherent light?

Answer 88

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.

Question 89

What is the law of reflection?

Answer 89

When a wave is reflected off of a surface, the angle of incidence is equal to the angle of reflection.

Question 90

What are the rules of refraction

Answer 90

Waves change speed when passing from one medium to another. The direction also changes when the incident ray is not on the normal.

Question 91

What are the rules of diffraction?

Answer 91

Waves spread out around corners. When passing through the gap the waves appear to curve if the gap is similiar to the wavelength.

Question 92

What is the interference?

Answer 92

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.

Question 93

What is constructive interference?

Answer 93

When two sets of waves meet in phase. Two crests meet or two troughs meet to produce a larger crest or trough.

Question 94

What is destructive interference?

Answer 94

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.

Question 95

What is path difference?

Answer 95

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.

Question 96

What is the maxima?

Answer 96

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.

Question 97

What is the minima?

Answer 97

It occurs at points of destructive interference. Path difference = (m+1/2) lambda

Question 98

Interference of sound

Answer 98

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)

Question 99

What needs to be in the same units when using the grating equation?

Answer 99

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.

Question 100

How do you increase theta (the separation of the maxima)?

Answer 100

Increase the wavelength (move from blue towards red light). Decrease the slit seperation ( have more lines per mm) Move the screen further away.

Question 101

Comparing spectra from prisms and gratings

Answer 101

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.

Question 102

Why is it necessary to use magnetic fields to contain plasma?

Answer 102

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.

Question 103

Why is an alternating supply used in a linear accelerator?

Answer 103

Particles always accelerate in the same direction (forwards). Force on particles is always in the same direction.

Question 104

Example Answer about electrons hitting a glowing surface and the surface increasing brightness 6????

Answer 104

Screen will be brighter, electrons will gain more energy and move faster.

Question 105

Why do lengths of tubes increase along a particle accelerator?

Answer 105

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.

Question 106

Comparing orders of magnitude questions:

Answer 106

Divide them, how many x10s

Question 107

How is this statement correct: all baryons are hadrons, but not all hadrons are baryons.

Answer 107

Baryons are hadrons as they are composed of three quarks. Mesons/ some hadrons are made from a quark- antiquark pair so are not baryons.

Question 108

Why can the gluon not be the force mediating particle for the gravitational force?

Answer 108

Because the strong force (gluons) have a short range. The gravitational force requires infinite range.

Question 109

Define the term fundamental particles

Answer 109

They cannot be composed of other particles.

Question 110

What is a meson made of?

Answer 110

An anti quark pair.

Question 111

Why can energy be released in a fusion reaction?

Answer 111

Because mass is converted into energy.

Question 112

When doing a light experiment, why may it be covered up?

Answer 112

To prevent reflections.

Question 113

Why may photoelectric not be ejected from a surface?

Answer 113

If the UV of the light is not high enough. If the frequency of the UV light is less than the threshold frequency.

Question 114

How are dark lines of sunlight produced in a spectra?

Answer 114

Photons of some energies/frequencies are absorbed in the suns outer atmosphere

Question 115

Why may the potion of lines be different in different spectra’s of galaxies?

Answer 115

Light is redshifted towards red as galaxies are moving away from the sun.

Question 116

What are three features of the Bhor model of the atom?

Answer 116

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.

Question 117

Why is a spectrum produced in a glass prisim?

Answer 117

Different frequencies/ colours have different refractive index. They are also refracted through different angles.

Question 118

What is one difference in the spectrum produced by a lower refractive index glass to a higher one?

Answer 118

Less deviation in the spectrum positioning.

Question 119

How does a greater refractive index cause more sparkles in the material?

Answer 119

Because the critical angle is smaller, and total internal reflection is more likely with the more refractive material.

Question 120

What is meant by the term ‘critical angle’?

Answer 120

The angle of incidence when the angle of refraction is 90^.

Question 121

Why may the lengths of a tube be increased when an alternating voltage is used in a particle accelerator?

Answer 121

As the speed of the particle increases, they travel further in the same time.

Question 122

Why are protons accelerated by an electric field?

Answer 122

Because they are positively charged and experience a force in an electric field.

Question 123

How is a minimum formed in an interference pattern?

Answer 123

Waves meet completely out of phase.

Question 124

What is meant by the term coherent?

Answer 124

The waves fork the two sources have a constant phase relationship and have the same frequency/wavelength and velocity.

Question 125

How is a maximum produced in interference?

Answer 125

When waves meet exactly in phase.

Question 126

If the distance between two gaps is increased in path different experiments, what will happen to the . Order maximum?

Answer 126

The path difference stays the same because the wavelength has not changed.

Question 127

What is the path different dependant on?

Answer 127

The wavelength - shorted wavelength, smaller path didference, sinO is proportional to lambda.

Question 128

Why might bright fringes be produced by waves meeting in phase?

Answer 128

Because the waves meet exactly in phase.

Question 129

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.

Answer 129

True

Question 130

What is irradiance?

Answer 130

When radiation falls on a surface, the irradiance is defined as the power per unit area. It can also be referred to as intensity.

Question 131

What is the units of irradiance?

Answer 131

Wm^-2

Question 132

What is an emission spectra?

Answer 132

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.

Question 133

What is the explanation of the emission spectra in relation to the Bhor model?

Answer 133

The electrons have different fixed energies in different orbits. They can move between each levels but cannot stop between them.

Question 134

Explanation of energy level diagrams

Answer 134

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.

Question 135

What is an emission line?

Answer 135

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. Different transitions produce different lines/frequencies of photons. The emission line will appear brighter if more electrons make that particular transition.

Question 136

What is an absorption line?

Answer 136

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.

Question 137

Relationship between frequency and wavelength - spectra.

Answer 137

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.

Question 138

What is the number of energy levels equivalent too?

Answer 138

The number of possible transmissions from a higher to a lower level.

Question 139

What is the absorption spectrum?

Answer 139

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.

Question 140

Absorption lines in the sun

Answer 140

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.

Question 141

Baryons

Answer 141

Composed of three quarks

Question 142

What is the photoelectric effect evidence of?

Answer 142

The particle model of light.

Question 143

As the refractive index of a medium increases, what else increases?

Answer 143

The frequency of the incident radiation increases.