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Physics > 4.1 Wave And Quantam Behaviour > Flashcards

4.1 Wave And Quantam Behaviour Flashcards

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1
Q

How do u calculate frequency with an oscilloscope?

A
  • measures voltage over time
  • move voltage per division and time per division dials to give waves
  • find time period and multiple by time per division
  • 1/T= frequency
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2
Q

How do u use standing waves to calculate the speed of sound?

A
  • Hollow tube in into measuring cylinder of water
  • get tuning fork and note down frquency
  • gently tap so sound wave travels and reflected at water surface where a node is formed
  • move tube up and down until u find shortest distance that it resoantes (makes loud sound)
  • measure distance (this is 1/4 wavelength)
  • find speed from v=f lambda
  • repeat w different frequencies
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3
Q

What is refraction?

A

When a wave changes direction as it enters a different medium

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4
Q

How does refraction occur?

A
  • When a ray enters mew medium some energy is reflected back and rest transferred into new medium
  • if it enters at and angle to the normal it changes speed
  • frequency is constant so also changes wavelength
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5
Q

If a ray of light travels into a more optically dense medium what happens.

A
  • if medium is denser then lught interacts w more particles so slows down more as more energy is transferred
  • the ray bends toward the normal
  • the wavelength decreases
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6
Q

What is absolute refractive index and how is it calculated?

A

-Ratio of speed of light in a vaccum to speed in that medium so is
n=c/cmedium

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7
Q

How do u calculate refractive index?

A

Sini / Sinr=C1/ C2=n2/n1

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8
Q

What can be said about airs refractive index?

A
  • Speed of light very similar to C so assume n is 1

- sini / sinr=n (of medium)

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9
Q

What is diffraction?

A

When waves spread out as they come through a small gap

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10
Q

How to show diffraction with a ripple tank?

A
  • change gap size

- most diffraction when gap is equal to wavelength

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11
Q

Showing diffraction with an obstacle

A
  • when a wave meets an obstacle it diffracts round the edges
  • forms triangular type of shadow behind obstacle
  • when length of obstacle gets larger than wave length the wave diffracts less so gives longer shadow
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12
Q

Explain diffraction of a beam of light through a split?

A
  • if wavelength of light wave is similar to the size of apeture split) u get light and dark fringes on a screen
  • bright central fringe w dark and brigth alternation fringes on either side decreasion in intensity as less photons incident per unit aread
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13
Q

Why is the brightest point the centre in a single split experiment?

A

Light travels in straight line so all waves are in phase

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14
Q

How to bright fringes appear in single split experiment?

A

-infinite sources of wavelets can interfere with each other
-Brightest fringe are in phase so point straight
For other bright points:
-constant phase difference
-so waves super impose but phasors are in slightly different directions
-form smaller resultant

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15
Q

Why do dark fringes appear in single split?

A
  • phase difference between waves give a resultant phasor of zero
  • phasor forms a loop
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16
Q

What has to be true about waves making a diffraction pattenr?

A

Need to be coherent ( same frequency and wavelength and comstant phase differentce)

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17
Q

How is double split set up?

A
  • when a laser is shined at a double slit it can act as two coherent point sources
  • the slits must be similar sized to wavelngth so light can be difffracted
  • a pattern of light and dark fringes appear depnding on constructive or destructive interferenc
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18
Q

What is youngs double slit formula

A

X (fringe spacing) =D (distance from screen) x wavelength / d (split spacing)

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19
Q

What is youngs double slit evidence for and what does it show?

A
  • wave nature of light

- shows diffraction and interference

20
Q

What dies a diffraction grating do for monochromatic loght?

A
  • lots of equally spaces slits
  • gives brighter and narrower fringes and darker dark fringes
  • because so many beams reinforce interfecenrce pattern
  • gives more accurate measurements
21
Q

What are zero, first and second order lines in light passed thrpigh diffraction grating?

A
  • maximum centre kine is zero order line

- next bright fringe out is first order and son on

22
Q

How do you derive youngs double slit from diffraction grating equation?

A
  • small angle approximation for first order tan feta= feta and sinfeta=feta
  • make a tan triangle
  • show X/D =tan feta = feta= sin feta (bc small angle)
  • sub in gives you Xd/D= wave length x 1 (n=1)
  • rearrangel for X
23
Q

How is a spectra produced from white light?

A

White light is a mixture of colours with different wavelengths

  • through a diffraction grating the patterns due to different wavelmgths are spread out by different ammounts
  • each order except the zero order become a spectra withe red on outside and violet on inside
  • the spectras help identify elements
24
Q

What is a photon

A

-discrete packets of energy called quanta

25
Q

What is an electron volt?

A

-kinteic energy gained by an electron when it is accelerated through a pd of 1 vold

26
Q

How are LEDs used to estimate Plancks constant?

A
  • LED of known wavelength in circuit placed in very dark room
  • slowly adjust power source until a cirrent just begins to flow and LEDlights up
  • record V ( threshhold voltage) across LED
  • repeat w different coloured LEDs of different wavelngths
  • plot V against frequency to get straight line graph of gradient h/e
  • multiply by e for h
  • repeat for average

-

27
Q

What does photoelectric effect show?

A

-particle behaviour of light

28
Q

Explain photo electric effect

A
  • when light hits its surface, metal is bombarded w photons
  • if one of these photons is absorbed by a free electron the electron gains E=hf energy
  • if its enough energy to break bonds holding it there its is emmited
29
Q

How does increase in light intensity affect photo elctrons?

A
  • each electron only absorbs one photon at a time so all energy for a release comes from one photon NOT a build up
  • so im reased light intensity (more photons) wont affect ke of electrons only frequency will
30
Q

Photo electric effect conclusions

A
  • For a given metal no photoelectrons emitted if radiation is below threshhold frequency
  • value of KE increases w frequency and uneffected by light intensity
31
Q

What is number of photo electrons emmited per second proportional to?

A

Intnesity

32
Q

Why cant photo electric effect be explaimed by wave theory?

A
  • according to wave theory even if light had a low frequency it would give a little bit of energy for eac hwave and build up over time
  • so the higher intensity the more energy so ke would increase w intensity but it doesnt
33
Q

Explain work function

A

-work function of a metal is energy needed to break bonds holding it there
-if energy gained is greater than work finction of metal electron is emitted
-if notmetal heats up
hf>work function

34
Q

Equation for work function

A

F=work function/h

35
Q

Explain energy levels

A
  • electrons exist in energy levels
  • it can move down by emitting a photon
  • energy carried by photon is equal to difference in energy levels
36
Q

How is a line emission spectra produced?

A
  • gas heated to high temp, excites atoms so moves electrons to higher energy levels
  • as they fall back to ground state certain photons emitted
  • split light thorugh a diffraction grating gives a line spectra
  • each line correspomds to particular wavelength of light emitted from the photons of soecific energies
37
Q

How is an absorbtion spectra formed.

A
  • white light passes through a cool gas most electrons are in ground state
  • photons of correct wavelengths are absorbed by electrons to excited them to higher energy levels
  • these wavelengths are then missing from spectrum
  • can work out elements in gas by which wavelengths are absorbed
38
Q

What can be said about photon paths?

A

-Photons take all possible paths at omce

39
Q

How to use phasors to find probability of arrival

A

-most paths cancel so consider straightest/quickest paths
-add phasors at the end of every path to give resultant phasor
-(longer paths will have rotated further as same frequency)
-probability is proportional to the resultant phasor squared
-

40
Q

Which path gives highest probaiblity

A

-quickest route as will contribute most to resultant amplitude

41
Q

Summary of electron diffraction

A

-electrons accelerated in a vaccum passed through graphite crystal and interact with the spaces to form rings of bright and dark fringes
-use phasors to find how likely it is, higher probability brighter point on screen
-evidnece for debrogile wavelngth as 1/2mv^2=hv/lambda
A higher voltage give higher Velocity gives smaller wavelength and smaller line spread
Which fits with lambda=h/mv

42
Q

Explain debrogile wavelength

A
  • says that particles display quantam bahvaioir

- increasing accelerating volatage increases speed so shorter wavelengths so smaller spread of lines

43
Q

How dpes E=hf differ for electrons

A

E is the kinetic energy

44
Q

When do electrons not show qunatam behaviour?

A
  • only diffract w objects of similar wavelengths

- shorter wavelngth diffracts less

45
Q

What is a standing wave, how do they form?

A

Standing waves form when two identical waves travelling in opposite directions superimpose forming nodes and anti nodes.
Usually a wave is reflected to form a standing wave

46
Q

What do bright and dark fringes show about probability of an electron arriving at a point?

A

Bright fringes show high probability as many electrons have arrived here and interference pattern has built up to make bright fringes

47
Q

How are we able to identify when an electron has hit the screen?

A

When electron hits screen photon is released

Physics (18 decks)

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