Toni atmosphere L6 Flashcards
(21 cards)
What are the two types of light scattering relevant to particles in aerosols
elastic scattering and inelastic scattering
What does elastic scattering involve
refraction, reflection and diffraction
What does elastic scattering lead to
Elastic scattering leads to a change in momentum of the light/ direction changes but not the energy
What does inelastic scattering involve
Absorption, fluorescence and Raman
What does inelastic scattering lead to
Inelastic scattering leads to a change in energy of the light
What does the size of the particle relative to the wavelength tell us
the size of the particle relative to the wavelength of light determines the dominant type of scattering
What does it mean is the particle size is much smaller relative to the wavelength
Describe using Rayleigh scattering
What does it mean if the particle size is comparable to the wavelength
describe using Mie theory
What does it mean if the particle size is much larger than the wavelength
Describe using geometric ray optics
What is the refractive index
The refractive index of a material is a measure of how much the speed of light is reduced when it passes through that material compared to its speed in a vacuum
How do we calculate the refractive index of a particle
N = n +ik
n is the real part - tells us how much light bends
k - complex part - controls how much light is absorbed
what is Rayleigh scattering
rayleigh scattering happens when light hits tiny particles, it makes the light scatter (bounces in different directions). The energy and the colour of the sight stays the same only the direction changes.
The light scattered in forward and backward direction is symmetric and independent of particle shape
when is Rayleigh scattering strongest
rayleigh scattering is strongest for shorter wavelengths. Which is why blue light gets scattered all around the sky making it look blue.
Scattered light is proportional to 1/wavelength ^4
What is Mie scattering
Mie scatter explains how medium sized particles scatter and absorb light
What is Mie theory
Mie theory predicts how much light is scattered and absorbed, and in which directions, when light hits a medium-sized particle
Describe the constraints for Mie theory
1) particles must be spherical
2) homogeneous - same material
3) plane wave light
4) monochromatic light
5) field is assumed to be time-harmonic
What does the size parameter tell us
It tells us how big the particle is compared to the light hitting it.
What is the scattering plane
The scattering plane is the flat 2D plane that contains:
The direction of the incoming light beam and the direction of the scattered light
What does it mean when θ = 0
forward scattering
What does it mean when θ=180
backward scattering
What does scattering look like in Mie theory
Not symmetrical like Rayleigh scattering. Mie scattering is often strongest in the forward direction.
It also includes side and backscattering, but forward scattering dominates, especially for larger particles.
