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optom > AAD light > Flashcards

AAD light Flashcards

1
Q

what is optics

A

branch of physics which describes the properties + behaviour of light + the interaction of light w matter

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2
Q

history of light
wave vs particle

A
  • Hooke & Huygens proposed that light existed as series of waves in hypothetical medium called ‘luminiferous aether’
  • Isaac Newton argued that light is comprised of particles which are emitted in all directions from a light source
  • light also only travels in straight lines + so can’t be a waveform as they were known to bend around obstacles
  • Faraday believed light was a high-frequency electromagnetic vibration, which could propagate even in absence of a medium
  • Hertz found that radio waves has same properties of visible light
    e.g. could be refracted (bend through medium) + reflected (bounce off medium)
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3
Q

wave vs particle investigations

A

by 19th century, wave theory generally accepted but could not explain some phenomena regarding light

  • Michelson-Morley experiment
  • photoelectric effect experiment
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4
Q

Michelson-Morley experiment
hypothesis

A
  • believed that light needed a medium to move in - ‘luminiferous aether’
  • if aether exists, light should travel faster when moving along aether than when moving against
  • devised experiment that split beam of light in 2
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5
Q

Michelson-Morley experiment
results

A
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6
Q

photoelectric effect experiment
hypothesis

A
  • if light is a wave, then any energy transfer would be related to intensity
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7
Q

photoelectric effect experiment
results

A
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8
Q

conclusion

A
  • Albert Einstein rvised Newton’s laws of motion to explain the constant speed of light revealed by M-M experiment
  • explained photoelectric effect by resurrecting the particle theory of light
  • concluded that light is a wave-particle duality; exhibits properties of both waves + particles
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9
Q

quantum theory

A
  • idea that visible light and other electromagnetic radiation is emitted in discrete packets of energy called quanta
  • photon
  • exhibit wave-particle duality
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10
Q

quantum theory

A

the idea that

  • the energy of a photon is proportional to its frequency
  • and inversely proportional to its wavelength

i.e. shorter wavelengths = higher energy + vice versa

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11
Q

quantum theory
equation

A

E = hv = (hc)/λ

where:

E = energy of a photon
h = Planck’s constant
v = frequency of the wave
c = speed of light
λ = wavelength of light

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12
Q

frequency

A
  • denoted by v
  • no. of complete waves produced in 1 second
  • measured in Hertz (Hz)
  • difference between 2 peaks/troughs
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13
Q

speed of light

A
  • velocity of light (v) is related to the frequency (v) and wavelength (λ)
  • units = ms-1
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14
Q

types of light sources

A

natural - e.g. sun
artificial - e.g. lamps, lasers

point - emits in all directions (almost never exist)
extended

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15
Q

electromagnetic spectrum

A

from left to right; short to long λs

  • λ measured in nanometres (nm)
  • 1nm = 1 x10-9 m
  • monochromatic = light comprised of 1 λ
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16
Q

visible spectrum

A
  • anything the human eye can detect
  • from ~400 to ~800
17
Q

electromagnetic spectrum

A

shorter λ; higher frequency; higher energy

  • cosmic rays
  • X-rays
  • UV
  • visible
  • infrared
  • micro-waves
  • radio-waves

longer λ; lower frequency; lower energy

18
Q

white light

A
  • not actually white
  • combination of some of the visible wavelengths of light
  • can be split into its constituent colours by a prism; dispersion
  • sun emits all λs of light
19
Q

how does light interact w objects?

A
  • transmission/refraction
  • absorption
  • reflection
20
Q

how do we perceive colour

A
  • white light from sun reaches object
  • some λs get absorbed by the object
  • some λs are reflected by the object
  • the reflected λs are what we perceive as colour

i.e. a yellow object is absorbing all the λs except the ones corresponding to the colour yellow

21
Q

absorption spectra

A
  • determines the absorption of a material
  • can be measured by a spectroscope
  • black lines represent what the sun absorbs; can be used to detect materials/gases that the sun contains/emits
  • called Fraunhofer lines
22
Q

emission spectra

A
  • if you raise these same gases to ‘incandescence’ they will emit the same wavelengths which can be measured as the emission spectra

-

23
Q

continuous vs discrete spectra

A

continuous = λs seamlessly blend together

discrete = individual λs are visible

24
Q

photopic sensitivity curve

A
25
Q

electromagnetic spectrum in the retina

A
26
Q

shadows

A
  • formed when passage of light is obstructed by an opaque object
  • because light rays travel in straight lines
  • when emitted from a point light source, shadow cast will have sharply defined edges
  • when emitted from an extended light source, shadow cast don’t have sharply defined edges; instead centre is uniformly dark (umbra) + the surround gradually fades to the periphery (penumbra)
27
Q

coloured shadows

A

optom (7 decks)

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