Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics GOIUYS > Nature of Light > Flashcards

Nature of Light Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

What is an electromagnetic wave?

A

transverse electric and magnetic waves oscillating perpendicular to each other

acceleration of a charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why do electromagnetic waves form?

A

a changing in E field creates a changing M field which creates a changing E field until infinity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How can EM waves move through vacuums?

A

the wave self propagates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Who was James Clark Maxwell and what did he do?

A

physicist who unified electricity and magnetism into electromagnetism as he found similarities between these two fields and predicted a spectrum of light

He proved:

  • light = EM wave with speed c (3x10^8 ms^-1)
  • light can be polarised since they’re transverse waves
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What do the 4 Maxwell Equations state?

A
  1. q/ε0 = total flux line in area (ε0 = vacuum permittivity)
  2. sum total of magnetic flux lines = 0
  3. voltage = EMF
  4. Ampere’s law w/ changing currents and areas considered
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How did Olaf Romer find c?

A

comparing how long the closest possible Io eclipse took to how long the furtherest possible Io eclipse took, he deduced it to be 2.12 x 10ms^-1

It was off because of inaccurate measurements of the distance of the earth’s orbit at the time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How did James Bradley find c?

A

Bradley used stellar aberration (taking earth’s orbit into consideration on how to actually view a planet), comparing angles to find c to be 3.03 x 10ms^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How did Fizeau/Foucalt find c?

A

using a cog wheel machine, Fizeau found the time it took for a cog tooth to fully block light equal to the 16km/c (distance of 8km reflected back to 16km over speed c since t = d/v) and calculated it to be 3 x 10^8ms^-1

Foucault a collaborator, later used more refined methods to get a measurement 0.5% off modern c

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why are UV, X-rays and Gamma rays so dangerous?

A

These lights contain incredibly high amounts of energy condensed into small wavelengths which can easily damage organic material i.e. humans

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens in an emission spectra?

A

a gas is excited, and whatever lights it emits is shone onto a spectroscope

It looks like a black background with thin strips of colour on it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What happens in an absorption spectra?

A

a gas is cooled, and a white light in shone in it. The gas will absorb some of this white light and the rest of it is shone onto a spectroscope

It looks like a complete ROYGBIV background with thin black strips on it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What relation does an emission spectra have to the absorption spectra?

A

The lines of light of an emission spectra fill in the blanks of the absorption spectra

This is because the thin lines of black represent the photons absorbed which later become emitted i.e. the thin lines of light of an emission spectra

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the two types of spectroscopes?

A

Prism spectroscope: source goes through a prism and then goes into your eye!

Diffraction grating: a majority of modern ones are these. They are either reflected on a reflection grating or go through a transmission grating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What can scientists gauge on a star with a spectra?

A 
structure
chemical composition
star velocity
temperature
density
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are the two models of light and who were they made by?

A

Christiaan Huygens - Wave model

Isaac Newton - Particle model

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What did the wave model state?

A
  • Light is propagated in ‘wavefronts’ from wavelets
  • Reflected on plane surfaces
  • Refracted on plane boundaries
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What did the particle model state?

A
  • Light is composed of ‘corpuscles’
  • They travel in a straight line
  • They speed up in denser mediums like glass because of attraction to the denser medium due to attractive forces (vector breakdown)
  • Different corpuscle sizes mean different colours
  • They are perfectly elastic
  • Rigid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why was the wave model disregarded in favour of the particle model in early optics?

A

Because Newton was a gee

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What couldn’t the particle model explain?

A
  • Denser medium speed thing (just wrong smh)
  • Refraction
  • Partial reflection
  • Diffraction, interference, polarisation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

When is diffraction most evident?

A

If the wavelength of the wave is same size as the slit it’s going through

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What was Young’s double slit and what did his experiment prove?

A

Light source → single slit → double slit → wall

That light has wave properties because of how they construct and destruct at certain points when shone at a wall as they got diffracted. This interference pattern is a result of a path difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the formula for Young’s double slit experiment?

A

y = mλL/d

y = length of centre of point on wall to m band
m = no. bright/dark spots from centre
λ = wavelength
L = distance from slits to wall
d = distance between slits
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the path difference length (l)?

A

dsinθ = mλ = l

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

In a double slit, the angle from centre to point is equal to (mathematically)?

A

tanθ = y/L

sinθ = mλ/d

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Draw a diagram of the double slit experiment

A

https://www.researchgate.net/profile/Michael-Mobley/publication/253374363/figure/fig1/AS:644285078728704@1530620941252/Diagram-of-Youngs-double-slit-experiment-indicating-the-intensity-of-light-striking-a.png

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is polarisation?

A

When light intensity reduces due to it going through a filter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is unpolarised and polarised light?

A

Unpolarised: before it goes through a filter

Polarised: after it goes through a filter, has its additional waves removed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What are examples of polarising mediums?

A

Shades of sunglasses, Radio transmission

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

If light moves through a polarising filter, what will the intensity out be?

A

Iout = 0.5Iin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Formula for polarisation with two filters?

A

Iout = Iin (cosθ)^2

This is called Malus’ law

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Types of polarisation?

A

Reflection and refraction:
reflection can remove a plane wave
refraction reduces intensity for perpendicular and parallel
e.g. light on a lake surface

Scattering:
light will be absorbed or re-radiated
reflection on surface of particle
e.g. light going through curtains going through dust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is a blackbody?

A

A perfect emitter AND absorber of light that falls into it. Its colour indicating the wavelength it is absorbing/emitting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What is blackbody radiation?

A

The energy intensity of radiation that the blackbody emits

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What are the order of colours of a blackbody?

A

None → Red → Orange → Yellow → White

rising intensity of energy, it becomes white because of the multiple light frequencies emitted all adding up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What was the classical model state would happen to blackbody radiation?

A

As the blackbody emitted radiation → temperature would increase into infinity because it is a continuous wave of energy
which is wrong experimentally

called the UV catastrophe

36
Q

How did Plank solve the UV catastrophe?

A

He proposed light was a continuous stream of packets of energy called quanta, rather than a continuous stream of a wave

note quanta = specific amounts

37
Q

What is the photoelectric effect?

A

The phenomena in which a light shone on something (usually a metal) causes electrons to be emitted

38
Q

Why did the photoelectric effect cause trouble for the classical model of light?

A
  1. Intensity (yes but no)
  2. Emission time
  3. Frequency
  4. Energy
39
Q

What did the classical model predict and what was the experimental data for emission time?

A

Classical prediction: Lower intensity meant significantly longer emission time

Experimental data: If emission occurred, it would always be essentially instant

40
Q

What did the classical model predict and what was the experimental data for frequency?

A

Classical prediction: Emission of photoelectrons independent of frequency

Experimental data: Emission of photoelectrons only occurred if certain frequencies were reached or surpassed

41
Q

What did the classical model predict and what was the experimental data for energy?

A

Classical prediction: Higher intensity = Higher energy in electrons (ALWAYS)

Experimental data: Energy of electron will increase UNTIL reaching a maximum energy point and followed the formula Emax = hf - φ

Where hf is the energy of the incident photon and φ is the least amount of energy it needs and Emax is the energy of the electron emitted

42
Q

What was the one feature that was predicted correctly (to some extent) by the classical model of light?

A

Intensity: Both classical predictions and experimental results stated that higher intensity means higher photocurrent

BUT experimental data shows that a photocurrent can only occur under certain frequencies

43
Q

What is the threshold frequency and what does it look like on a Energy-frequency graph?

A

The smallest frequency (fo) necessary for photoemission

It is the x-intercept on a Energy-Frequency graph

44
Q

What is the work function and what does it look like on a Energy-frequency graph?

A

The smallest energy (φ) necessary for photoemission

It is the y-intercept on a Energy-Frequency graph AND it is ALWAYS under 0 (but the φ has a positive value)

45
Q

Energy is dependent on what?

A

Frequency, because Ep = hf

46
Q

Intensity is independent of what?

A

Energy (of single photon), because Ep = hf

Intensity means the no. photons in a given area, it doesn’t say anything about how much energy is in the photons

47
Q

How can you calculate the total energy of something if you are given the number of photons and the energy of the individual photons?

A

Et = nEp

Et = total energy
n = no. photons
Ep = energy of individual photon = hf
48
Q

What are Einstein’s two postulates?

A
  1. Inertial frameworks are the same for everyone

2. c is constant for everyone doesn’t matter how fast someone or something is moving

49
Q

What is proper time (to)?

A

The time in which the near light speed event is occurring

50
Q

What is dilated time (t) and how do you find it?

A

The time that is increased

t = to/√(1-(v^2/c^2))

51
Q

When a stationary person A observes another person B going very fast, how will these people’s time appear to look like to each other?

A

Slower compared to themselves

52
Q

What is proper length (lo)?

A

The length of un distorted thing

53
Q

What is contracted length (l) and how do you find it?

A

The length that is shrunken down

L = Lo x √(1-(v^2/c^2))

54
Q

When a stationary person A observes another person B going very fast, how will these people’s lengths appear to look like to each other?

A

Shortened

55
Q

What is rest mass (mo)?

A

The mass of something stationary

56
Q

What is relativistic mass (m) and how do you find it?

A

The mass of something moving at near light speeds

m = mo/√(1-(v^2/c^2))

57
Q

When a stationary person A observes another person B going very fast, how will these people’s mass appear to look like to each other?

A

Heavier (more mass)

58
Q

What does E = mc^2 state pretty much?

A

Mass and energy are the same thing shown differently

59
Q

What is the more technically correct version of the energy-mass equivalence equation?

A

E = 1/2mv^2 +moc^2

60
Q

What is an inertial frame of reference?

A

When you are stationary or moving at a constant linear velocity i.e. you are not accelerating/rotating

and where Newton’s 1st law is obeyed

you FEEL stationary

61
Q

What was the Michaelson-Morley experiment?

A

An experiment to determine the existence of the aether

62
Q

What was the Michaelson-Morley experiment’s method?

A

They spun a wheel that shone light on a half reflecting mirror at 90°. When the two light beams met, they should have an interference pattern different to if it weren’t spun

63
Q

What did the Michaelson-Morley experiment end with?

A

They couldn’t conclude anything from the result i.e the null hypothesis

64
Q

What was the problem with measuring the speed of light before 1950?

A

Machines were not precise enough to measure at such short times or lengths

65
Q

How many equations did Maxwell have initially?

A

He had 20 but they were cut down to just 4

66
Q

What is Hertz’s contribution to discovering the properties of light?

A

He found ‘invisible’ radio waves from spark gaps which behaved like visible light (same speed)

Gave credence to Maxwell’s theory

67
Q

What spectra is typically used for stars and their temperature?

A

Absorption spectrum

68
Q

What is a red shift and a blue shift?

A

The spectra measured will move to the red side if it’s travelling away from us and to the blue side if it’s moving towards us

69
Q

All hot objects no matter composition do what?

A

Emit radiation

70
Q

Where do ‘cooler things’ and ‘warmer things’ go on a blackbody graph respectively?

A 
cool = blue side
warm = red side
71
Q

What are these blackbody curve graphs, graphs of?

https://preview.redd.it/699cgiciig371.jpg?width=640&crop=smart&auto=webp&s=4430689249a1b5d213eb6946b35c03941ef3b6c8

A

https://preview.redd.it/ezetwjwaig371.jpg?width=960&crop=smart&auto=webp&s=c3979cc0913b920733cf5a7bb6d5d72adafe30b2

72
Q

Diffraction gratings… What are they and why?

A

They’re light shone through a number of really thin gaps

They create a pattern that’s white, then a number of inverse prisms the gaps that widen as they go

https://www.newport.com/mam/celum/celum_assets/Figure_79-Photonics_Handbook_800w.jpg

73
Q

What is so cool about diffraction gratings?

A

They are much more precise compared to double slits

74
Q

With two polarising filters, what are the first and second filters called?

A

Polariser

Analyser

75
Q

Formula for Double Slit Experiment?

A

y = mLλ/d

[y = distance from centre (m)]
[L = distance from screen (m)]
[d = distance between slits (m)]
76
Q

Formula for Wave Difference?

A

d sinθ = mλ

[d = distance between slits (m)]

77
Q

Formula for Polarisation?

A

Io = Ii (cosθ)^2

note Ii is the light before the analyser and Io is the light after the analyser and Ii = I/2 where I is unpolarised light (before polariser)

78
Q

Formula for Maximum Kinetic Energy of Photoelectron?

A 
Kmax = qVstop = 1/2mv^2
Kmax = hf - Φ
Kmax = h(f - fo)
[Φ = hfo (fo = minimum frequency)] 
[h = 6.626 x 10^-34]
79
Q

Formula for Kinetic Energy of Photon?

A

E = nhf

[n = number of photons]

note n is usually just 1 unless stated otherwise i.e. total energy will require you to use E = nhf

80
Q

Formula for Wien’s Law?

A

λmax = b/T

[λmax = greatest wavelength (m)]
[G = wien's constant (2.898x10^-3)]
81
Q

Formula for Time Dilation?

A

t = to/√(1 - (v^2/c^2))

[to = time in perspective of fast moving thing (secs)]
[t = time observed by slow fellas (secs)]
[c = speed of light (3x10^8)]
82
Q

Formula for Length Contraction?

A

L = Lo√(1 - (v^2/c^2))

[Lo = length of fast moving thing (m)]
[L = length observed by slow fellas (m)]
[c = speed of light (3x10^8)]
83
Q

Formula for Relativistic Mass?

A

m = mo/√(1 - (v^2/c^2))

[mo = rest mass (kg)]
[m = mass observed by slow fellas (kg)]
[c = speed of light (3x10^8)]
84
Q

Formula for Relativistic Momentum?

A 
p = mov/√(1 - (v^2/c^2))
p = mv
[mo = rest mass (kg)]
[m = relativistic mass (kg)]
[c = speed of light (3x10^8)]
85
Q

Formula for Mass-Energy Equivalence?

A

E = mc^2

[c = speed of light (3x10^8)]

Physics GOIUYS (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions