How a receiving material responds to an interaction with light depends on 2 things: Frequency of the incoming light Natural frequency of the object being hit

If incoming frequency matches natural

frequency, resonance occurs!

If incoming frequency matches natural

frequency, resonance occurs!

Individual atoms! Atoms of different elements hold onto their

electrons with different amounts of strength. We will represent this as “spring strength.”

The resonance that occurs can cause light to be re-

emitted!

The resonance that occurs can cause light to be re-

emitted!

Different frequencies of light hit identical atoms

No match, little vibration…

Good match, large vibration!

Light of same frequency hits different atoms

No match, little vibration…

Good match, large vibration!

Light can interact with matter in several ways.

Can you think of them and give an example of each???

Will the interaction result in transparency or opacity?

Reflection off of the surface (Opaque)

Reflection off of the surface (Opaque)

Absorption resulting in energy lost to heat

(Opaque)

Absorption resulting in energy lost to heat

(Opaque)

Absorption and re-emission resulting in delayed transmission

(Transparent)

Absorption and re-emission resulting in delayed transmission

(Transparent)

Reflection off of the surfaceReflection off of the surface

Shiny Surface

Atoms

Incoming light

Reflected Light

Excited atom

vibrates and

immediately re-emits

light

Metals are shiny because the light that shines on them forces free electrons into vibration. These electrons emit their own light as a reflection.

Reflection off of the surfaceReflection off of the surface

Absorption and re-emission resulting in delayed transmission (Transparent)

Absorption and re-emission resulting in delayed transmission (Transparent)

Incoming light

Transmitted light

Atom absorbs

light, vibrates,

and re-emits

Delay from repeated

absorption and re-emission makes light slower in

medium

Transparent material (glass)

Absorption resulting in energy lost to heat (Opaque)

Absorption resulting in energy lost to heat (Opaque)

Incoming light

Light hits atom at

matching frequency

and vibrates a

lot!

Energized atom

begins bumping into other atoms and

causes temperatur

e of material to

rise.

Visible light can get through glass windows

Glass blocks infrared and UV waves causing the glass to warm up.

Absorption and re-emission resulting in delayed transmission (Transparent)

Absorption and re-emission resulting in delayed transmission (Transparent)

Absorption resulting in energy lost to heat (Opaque)

Absorption resulting in energy lost to heat (Opaque)

Luckily our atmosphere is mostly opaque to UV light due to scattering.

Clouds still transmit some UV light, hence sunburn on a cloudy day.

Sand and water can reflect UV light, so you can get a tan even when under your umbrella!

Light is slower than when in a vacuum in all other media! In water- 75% c In Glass- 67% c In Diamond- 40% c

Depends on the index of refraction (n)

vcn

n1