Properties of Light
Properties of Light
• Effects of Materials on Light• Reflection• Refraction• Dispersion• Total Internal Reflection• Interference• Diffraction• Scattering of Light• Polarization
Effects of Materials on Light
Materials can be classified based on how it responds to light incident on them:1. Opaque materials – absorb light; do
not let light to pass through2. Transparent materials – allow light to
easily pass through them3. Translucent materials – allow light to
pass through but distorts the light during the passage
ReflectionLight follows the Law of Reflection: “The angle of incidence is equal to the angle of reflection.”
Light can bounce off materials in two ways:1. Diffuse reflection – reflected rays go in
different directions; happens in rough-textured or uneven surfaces
2. Regular/Specular reflection – reflected rays go in one directions; happens in smooth and shiny surfaces; image can be seen
RefractionLight bends/refracts when it changes speed.
This usually happens when the light travels from one medium to the next.
Simple rule of thumb in refraction:• If light slows down, it will refract towards
the normal line.• If light speeds up, it will refract away from
the normal line.
RefractionLight travels faster in air, slow in water and slower still in glass.The slower light is in a medium, the more it refracts/bends in it.The measure of how much light refracts in a medium is called index of refraction.
Medium Index of Refraction (n)
air 1.000293
water 1.3330
glass 1.490
diamond 2.419
RefractionLight follows the Law of Reflection: “The angle of incidence is equal to the angle of reflection.”
Light can bounce off materials in two ways:1. Diffuse reflection – reflected rays go in
different directions; happens in rough-textured or uneven surfaces
2. Regular/Specular reflection – reflected rays go in one directions; happens in smooth and shiny surfaces; image can be seen
RefractionLight follows the Law of Reflection: “The angle of incidence is equal to the angle of reflection.”
Light can bounce off materials in two ways:1. Diffuse reflection – reflected rays go in
different directions; happens in rough-textured or uneven surfaces
2. Regular/Specular reflection – reflected rays go in one directions; happens in smooth and shiny surfaces; image can be seen
DispersionThe process in which light is separated into its colors due to the differences in degrees of refraction.
How are rainbows formed?
Total Internal ReflectionWhen light is reflected completely at the boundary between two mediums
How do fiber optics work?
Why do diamonds sparkle so much?
DiffractionLight spreads out after passing through/by an opening /edge.The opening must be very narrow for diffraction of light to occur.
“Every cloud has a silver lining.”
InterferenceLight can superimpose and have either constructive interference or destructive interference.
Reflection
• Reflection - Light bounces off the surfaces like mirrors such that the angle of incidence is equal to the angle of reflection.
• Refraction - Refraction is defined as the bending of light as it passes through materials of different optical density
• Interference - When two light waves meet or coincide, it can create either constructive or destructive interference based on how the crests & troughs of the waves meet.
Wave Properties (Light)
• Diffraction - This is defined as the bending of light waves around obstacles in its path. Example, when a light wave passes through a barrier with a small opening, it acts as a single point source from where light emerges and spreads in all direction.
• Light has a dual nature.• Depending on the phenomenon or behavior in
question, light can be treated either as a wave or as a particle.
• To examine this wave-particle duality, we will examine two experimental proofs.
So, is light a wave or a particle?
• Conducted by Thomas Young in the early 1800’s• Provided an experimental basis for considering light as
a wave.
Light is a WAVE: Young’s Double-Slit Experiment
• The individual slits acted as individual sources which light passes through and spreads. (Isn’t this like water waves?)
• Light exhibits interference which is a wave property.
Key Points of Young’s Experiment
• Explained by Einstein during the early 1900’s
• Provided an experimental basis for considering light as a particle.
• Einstein earned a Nobel Prize for his explanation.
Light is a PARTICLE: The Photoelectric Effect
• Higher energy light knocks off electrons at higher energy.
• The number of ejected electrons is directly related to the intensity (brightness) of light. This means brighter lights emit more photons.
• Light is a particle since it is capable of ‘knocking off’ electrons. Further, unlike waves, increasing the brightness does not increase the energy of the knocked off electrons.
Key Points of Photoelectric effect
