AAD light

Question 1

what is optics

Answer 1

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

Question 2

history of light
wave vs particle

Answer 2

• 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)

Question 3

wave vs particle investigations

Answer 3

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

• Michelson-Morley experiment
• photoelectric effect experiment

Question 4

Michelson-Morley experiment
hypothesis

Answer 4

• 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

Question 5

Michelson-Morley experiment
results

Question 6

photoelectric effect experiment
hypothesis

Answer 6

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

Question 7

photoelectric effect experiment
results

Question 8

conclusion

Answer 8

• 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

Question 9

quantum theory

Answer 9

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

Question 10

quantum theory

Answer 10

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

Question 11

quantum theory
equation

Answer 11

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

Question 12

frequency

Answer 12

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

Question 13

speed of light

Answer 13

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

Question 14

types of light sources

Answer 14

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

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

Question 15

electromagnetic spectrum

Answer 15

from left to right; short to long λs

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

Question 16

visible spectrum

Answer 16

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

Question 17

electromagnetic spectrum

Answer 17

shorter λ; higher frequency; higher energy

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

longer λ; lower frequency; lower energy

Question 18

white light

Answer 18

• 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

Question 19

how does light interact w objects?

Answer 19

• transmission/refraction
• absorption
• reflection

Question 20

how do we perceive colour

Answer 20

• 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

Question 21

absorption spectra

Answer 21

• 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

Question 22

emission spectra

Answer 22

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

-

Question 23

continuous vs discrete spectra

Answer 23

continuous = λs seamlessly blend together

discrete = individual λs are visible

Question 24

photopic sensitivity curve

Question 25

electromagnetic spectrum in the retina

Question 26

shadows

Answer 26

• 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)

Question 27

coloured shadows