The Wave Nature of Light (18)

Question 1

Young’s Double Slit Experiment

Answer 1

• demonstrates wave nature of light
• monochromatic light source is diffracted twice and produces two coherent waves
• constructive interference - produces bright fringes
• destructive interference - produces dark fringes

Question 2

Diffraction Grating

Answer 2

• modern, narrower version of young’s slits which causes light to diffract more

Question 3

Grating Constant

Answer 3

• d = 1/N
• d = grating constant
• N = number of lines per metre

Question 4

demonstrating the wave nature of light

Answer 4

• laser = monochromatic source
• diffraction grating
• middle dot = zero order (n=0)
• 1st order (n=1) ..

Question 5

wavelength of light

Answer 5

• nλ = dsinθ
• n = order of image
• d = grating constant
• θ = angle of diffracted light from normal
• Derivation

Question 6

Light as a transverse wave

Answer 6

• Reflection - glare from windows
• Polarisation - reduce glare by looking through polaroid sheet
• Bright light - polaroid sunglasses reduces the amount of light entering our eyes
• Stress testing - models made from clear plastic, placed between two pieces of polaroid at 90 degree angles to eachother, stress points can be identified when illuminated

Question 7

Dispersion

Answer 7

• the separation of light into its constituent colours

Question 8

prism

Answer 8

• disperses light according to its speed in the media
• blue refracts most, red refracts least
  (different wavelengths refract at different angles)

Question 9

grating

Answer 9

• diffracts the light according to its wavelength sizes
• red diffracts the most, blue diffracts the least
  (different wavelengths diffract differently)

Question 10

white light spectrum

Answer 10

caused by diffraction/dispersion

Question 11

Primary Colours

Answer 11

• the three colours that combine to make white light
• red
• green
• blue

Question 12

secondary colours

Answer 12

• when any two primary colours are combined
• red + green = yellow
• red + blue = magenta
• blue + green = cyan

Question 13

complementary colours

Answer 13

• primary and secondary colours that combine to give white light
• opposite from each other
• red + cyan = white
• green + magenta = white
• blue + yellow = white

Question 14

recombination

Answer 14

• opposite of dispersion

- creating white light by combining colours

Question 15

Electro Magnetic Waves

Answer 15

• Don’t need a medium to travel through
• cause electrical and magnetic disruption
• can travel in a vacuum
• travel at the speed of light c = 3 × 10^8 m/s
• display the phenomena of waves including polarisation as they are transverse

Question 16

Infrared

Answer 16

• all hot objects emit
• uses = thermograms (used to find missing persons, detects life)
  = remote controls

Question 17

Ultraviolet

Answer 17

• causes sunburn, cancer, production of vitamin D
• uses = photoelectric effect
  = darkening skin
• causes florescence in whitening products and vaseline
• cannot pass through glass

Question 18

Measuring IR and UV

Answer 18

• white light through quartz prism
• IR - thermometer just outside red end
• UV - vaseline just outside violet end

Question 19

Spectrometer

Answer 19

• used to examine spectra of light and calculate wavelength

Question 20

heavy base

Answer 20

• keeps it steady

- vernier scales on it

Question 21

Vernier scale

Answer 21

measures angle of deviation (for eq)

Question 22

turntable and levelling screws

Answer 22

allow grating to be positioned correctly

Question 23

collimator

Answer 23

• a slit through which light passes
• a convex lens 1 focal length away (II) which focuses light onto grating
• collimates light ( parallel light required for interference)

Question 24

telescope

Answer 24

• can be rotated to find each order

- associated angle read