Particles And Waves Flashcards Preview

Higher Physics > Particles And Waves > Flashcards

Flashcards in Particles And Waves Deck (19):
1

The atom

• basic unit of matter

• central nucleus has +ve charge, made of protons and neutrons

• Electrons orbit nucleus in energy levels at high speeds. The lowest energy level is known as the ‘ground state’, and higher energy levels are known as ‘excited states’.

• overall charge is neutral

• proton (p) has a mass of 1amu and charge of +1

• neutron (n) has a mass of 1amu and no charge

• electrons (e) has a negligible mass and a charge of -1

2

Isonisation

• is the addition/ removal of an electron from an uncharged atom

• when this happens the electron has reached the ‘ionised state’ and has zero potential energy (therefore electrons in the energy levels have a negative potential energy value)

3

Charge

• Electric charge (coulombs) = current (amps) x time (seconds), Q (C)= I (A) x t (s)

• Work done (joules) = electric charge (coulombs) x voltage (volts), W (J) = Q (C) x V (V)

• Opposite charges attract, similar charges repel

4

Electric field

• Region of charge where another charge will experience a force

• Shown by field lines, and arrows on them represent how a +ve charge would interact with the force. The closer together the field lines the stronger the force.

5

Magnetic field

• Magnets have a north and south pole

• Opposite poles attract, similar poles repel

• A magnetic field is a region of space around a pole where another pole will experience a force

• A magnetic field is represented by field lines, which have arrows showing the direction a north pole would experience this force. The closer together the field lines the stronger the force.

• A magnetic field also exists round a current-carrying conductor

• When a current-carrying conductor passes through a magnetic field it experienced a force die to the interaction of the magnetic field produced by the the conductor itself and the magnetic field it is passing through. The direction of this force is perpendicular to the direction of the current and perpendicular to the direction of the magnetic field.

6

Particle accelerators

• In particle accelerators charged particles are accelerated by electric fields and (if required) magnetic fields are used to change the direction of their path

• The collisions of these charges particles with static targets or other charged particles can then be used to study the nature of matter and/ or fundamental forces

7

Photoelectric emission

• Photoelectric emission is when electromagnetic radiation (incident light) strikes a metal surface causing electrons to be emitted

• For this to occur the incident light must be above a certain frequency (ie. the threshold frequency - fo), which is different for each metal

• For this to occur the metal must have an energy above a certain value (ie. the work function - Eo)

• If the energy of the incident photon is greater than the work function then the excess energy will supply the electron with kinetic energy: Ek = E - Eo

• In photoelectric emission each electron can only absorb the energy of a single photon at one time

• Photoelectric emission proves that electromagnetic radiation is not a continuous wave but is made up of quanta (wave packets) called photons, this concept is known as wave-particle duality.

8

Irradiance

• Irradiance is the power per unit area of a point source incident on a surface (units = Wm^-2)

• Irradiance = power / area , I = P/A

• Irradiance1 x distance1^2 = irradiance2 x distance2^2 , I1d1^2 = I2d2^2

• A point source emits radiation uniformly in all directions

9

Isotopes

• Isotopes are atoms of the same element with a different number of neutrons in the nucleus

• Radioactive isotopes emit nuclear radiation to achieve stability

• Types of radioactive decay include:
— alpha (α) which is a helium nucleus with an atomic mass 4amu and charge of +2
— beta (β) which is a fast moving electron with negligible mass and a charge of -1
— gamma (γ) which is an electromagnetic wave with no mass or charge and infinite range

10

Nuclear fusion

• When small molecules going to form a larger molecule with the release of energy and neutrons.

• It requires extremely high temperatures to create plasma (state of matter where electrons have sufficient energy to be ionised from their atoms) in which nuclear fission can take place.

• This creates difficulties to find a suitable coolant (so useful energy and can be extracted) and a suitable containment (so the high temperature of plasma won’t melt the container) when artificially inducing the reaction.

• In these reactions there is often a lost mass that has been converted to energy. This can be calculated by E = mc^2

11

Nuclear fission

• When a large nucleus is split into smaller nuclei with the release of energy and neutrons

• This can be spontaneous or induced by a neutron

• In these reactions there is often a lost mass that has been converted to energy. This can be calculated by E = mc^2

12

Continuous spectrum

• A continuous spectrum contains all the possible frequencies of radiation

• It is produced when energy is applied to solids liquids and high-pressure gases

13

Line emission spectrum

• Line emission spectra look like coloured lines on a black spectrum

• Line emission spectrum are produced when photons of radiation are emitted by electrons moving down energy levels

• This happens when energy is supplied to low-pressure gases

• Each element produces a unique line emission spectrum as the number of lines on the spectrum correspond to the number of possible electron transitions in that element

14

Absorption spectrum

• An absorption spectrum appears as black lines on a continuous spectrum.

• They are produced when electrons absorb photons of radiation and move up energy levels.

• This occurs when light with a continuous spectrum passes through low-pressure gas.

• The lines on an absorption spectrum are in the same position as the same elements lines on emission spectrum

• Fraunhofer lines are the lines visible in the sun’s absorption spectrum due to the gases present in the sun’s atmosphere

15

Interference

• Constructive interference occurs when two waves meet in phase (ie. crest to crest, trough to trough), resulting in an increased amplitude of the wave

• Destructive interference occurs when the two waves meet completely out of phase (ie. crest meets trough), resulting in the waves cancelling each other out

• Coherent waves have the same frequency, wavelength and velocity so are either in phase or have a constant phase difference. The path difference from two coherent sources can result in interference patterns arising

• When the path difference between the waves is equal to a whole number of wavelengths the waves will meet at a position of maxima and undergo constructive interference. [ path difference = m (position of maxima reached) λ ]

• When the path difference between the waves is equal to an odd number of half-wavelengths the waves will meet at a position of minima and undergo destructive interference. [ path difference = (m + 1/2) (position of maxima prior to position of minima reached) λ ]

• The central maxima (m=0) is the point where two coherent waves have travelled the same distance

16

Diffraction grating

• A diffraction grating consists of many many equally spaced slits that are extremely close together.

• When the waves diffract through the slits they interact with waves they interact with the waves from the neighbouring slits to produce a clearer interference pattern (of alternating constructive and destructive interference)

• When white light is passed through a diffraction grating multiple (not very bright) spectra are observed about the central (white) maxima. In the spectra red light is deviated the most and violet light is deviated the least (ie. violet light is closest to the centra maxima). The spectra produced are widely dispersed. [ dsin θ = m λ ]

17

Refraction

• Refraction is the change in speed of light (which often results in a change of direction) when it travels from one medium into another

• When the incident light travels from a less dense to a more dense medium the ray of light will refract towards the normal

• When the incident light tracked from a more dense to less dense medium the ray of light will refract away from the normal

• Partial internal reflection occurs when the incident light passes from a slow to fast medium at an angle of incidence less than the critical angle, causing most of the light to be refracted away from the normal and some of the light to be reflected back inside the slow medium

• When the incident light passes from a slow to fast medium at the critical angle (θc) the angle of refraction in the fast medium is 90 degrees

• Total internal reflection occurs when the incident light passes from a slow to fast medium at an incident angle greater than the critical angle, causing all the light to be reflected back inside the slow medium

18

Refractive index

• The refractive index of a medium is defined as the ratio of the speed of light in a vacuum (/air) to the speed of light in the medium

• n (refractive index) = v1 (in air)/ v2 = sin θ1 (in air/ sin θ2 (θ is the angle of incidence/ refraction) = λ1 (in air)/ λ2

• The refractive index of a material varies slightly with frequency. The refractive index of a medium for violet light is greater than the refractive index of a medium for red light, (ie. the greater the wavelength, the lesser the refractive index).

• This is the reason why when white light is passed through a prism a (bright yet narrow) spectrum is produced. When this happens the red Libby is deviated the least and violet light the most.

19

The standard model

• Fundamental particles are made up of matter particles and force medicating particles

• All fundamental particles have an equivalent antimatter particle, which has the same mass but opposite charge [eg. ū (u-bar) ]

• Matter particles are made up of leptons and quarks

• Leptons = electron, electron neutrino, muon, muon neutrino, tau, tau neutrino

• Quarks = up, down, strange, charm, top, bottom

• Quarks never exist alone, so combine to form hadrons which can be further classified as a meson or baryon. A meson is the result of two combined Quarks, whereas a baryon is the result of three Quarks combining.

• Fundamental forces each have an associated force medicating particle

• Fundamental forces:
>>Gravitational force - force of attraction between objects with mass, weakest fundamental force, associated force mediating particle is the graviton
>>Electromagnetic force - affects particles with charge, associated force medicating particle is the photon
>>Weak nuclear force - associated with beta decay, only acts over distances on a nuclear scale, associated force medicating particle is the W and Z bosons
>>Strong nuclear force - force that holds Quarks together to form particles, and holds particles together to form nuclei, only acts over distances on a nuclear scale, strongest fundamental force, associated force medicating particle is the gluon

• Fermions = matter particles (leptons + quarks) and baryons

• Bosons = force mediating particles and mesons

• The Higgs Boson is also apart of the standard model and attributes to the mass of other particles