L10(b) Interaction of light with matter

Question 1

what is scattering

Answer 1

scattering of light occurs when a beam of light is broken into several smaller, less intense beams of light by gases, aerosols or particulates in the atmosphere. dependent on (1) size of particle (2) distance between particles

Question 2

explain incoherent scattering

Answer 2

when spacing between particles is much greater than wvl of incident light

1. larger particle size
   eg. mist, clouds, fog
   - light scatters more forward direction of incident light
   - wvl independent
   - follows reflection/refraction of light in geopt
   - all wvl scattered equally
2. smaller particle size
   - light scatter in ALL direction
   - wvl dependent
   - short wvl scatter > long wvl

Question 3

explain coherent scattering

Answer 3

when particles are closer together as compared to wavelength of incident light

• involved with transmission of light through transparent material
• has constant phase difference
• wvl independent hence equal wvl scattering

Question 4

explain colour perception of skies and sunsets/rises

Answer 4

skies are blue because sunlight hits the atmosphere where the gases scatter the shorter wavelengths of blue light

sunsets/rises are red because they are lower in the sky and have to pass through more of the atmosphere to reach the eye, so more blue wavelength is lost, resulting in red observed

Question 5

what is dispersion

Answer 5

separation of white light into different spectrums of wavelengths after refraction

Question 6

explain dispersion

Answer 6

• different frequencies of EM radiation travel through a material at different VELOCITIES
• light of different wavelengths REFRACT by different amounts when passing one medium to another of different index
• shorter the wavelength (higher frequency) the more it’s refracted
• responsible for chromatic aberration

Question 7

explain dispersion and rainbow formation

Answer 7

rainbow forms when sun appears in the sky after rain

• MOISTURE in the atmos behaves like PRISMs, dispersing sun’s rays into seven colours
• red appears at top, violet at bottom
• light undergoes total internal reflection in tiny water molecules