Download ppt - Light and Reflection Light and Reflection. Characterization of Light Light has both a wavelike and particle like nature. Light has both a wavelike and

Light and Light and ReflectionReflection

Characterization of LightCharacterization of Light Light has both a wavelike and particle Light has both a wavelike and particle

like nature.like nature.

Electromagnetic wave theoryElectromagnetic wave theory: Light is a : Light is a wave composed of oscillating electric and wave composed of oscillating electric and magnetic fields (magnetic fields (electromagnetic waveelectromagnetic wave).).

These waves propagate transversely at These waves propagate transversely at right angles to each other.right angles to each other.

Oscillating Oscillating Magnetic Magnetic FieldField

Oscillating Oscillating Electric FieldElectric Field

Characterization of LightCharacterization of Light

All electromagnetic waves travel All electromagnetic waves travel at the speed of light (c). at the speed of light (c).

Electromagnetic waves vary Electromagnetic waves vary depending on frequency and depending on frequency and wavelength.wavelength.

These differences account for the These differences account for the broad range in the broad range in the electromagnetic spectrum.electromagnetic spectrum.


The speed of light in The speed of light in a vacuum = a vacuum =

2.99792458 x 102.99792458 x 108 8 m/sm/sThe speed of light in The speed of light in air = 2.99709 x 10air = 2.99709 x 108 8

m/sm/sWe use 3 x 10We use 3 x 108 8 m/sm/s

Electromagnetic Electromagnetic SpectrumSpectrum

The same relationship between The same relationship between frequency, wavelength, and speed frequency, wavelength, and speed that exists in sound waves or that exists in sound waves or objects undergoing SHM also holds objects undergoing SHM also holds true for electromagnetic waves. true for electromagnetic waves.


νν = = f f λλ

c = c = f f λλ

Huygen’s PrincipleHuygen’s Principle

Electromagnetic waves travel in Electromagnetic waves travel in wave fronts.wave fronts.

Wave fronts are made up of many Wave fronts are made up of many wavelets, each containing a “point wavelets, each containing a “point source”. If you make a line tangent source”. If you make a line tangent to each point source, you have to each point source, you have identified a new wave front.identified a new wave front.


Characterization of LightCharacterization of Light Huygens Huygens Principle can Principle can describe waves describe waves interacting with interacting with matter matter (diffraction) or (diffraction) or waves moving in a waves moving in a straight line.straight line.

The The perpendicular perpendicular direction in which direction in which the wave front is the wave front is moving is referred moving is referred to as ato as a “ray”.“ray”.

Wave front motion as it moves Wave front motion as it moves around an objectaround an object


Light becomes more spread out and Light becomes more spread out and there is less light available per unit there is less light available per unit area.area.

Inverse relationship between brightness and Inverse relationship between brightness and distancedistance..

Brightness decreases by the square of Brightness decreases by the square of the distance from the source.the distance from the source.

ex. There is ¼ as much light falling on a ex. There is ¼ as much light falling on a particular spot 2 m away than there is light falling particular spot 2 m away than there is light falling

on the same spot that is 1 m away.on the same spot that is 1 m away. (fig 14-4 pg. 525)(fig 14-4 pg. 525)


Waves can be approximated as rays.Waves can be approximated as rays. Brightness of light decreases by the Brightness of light decreases by the

square of the distance from the square of the distance from the source.source.

ReflectionReflection Refers to the turning Refers to the turning

back of an back of an electromagnetic electromagnetic wave (light ray) at wave (light ray) at the surface of a the surface of a substance.substance.

Depending on how Depending on how smooth the smooth the reflecting surface is, reflecting surface is, the reflection will the reflection will either beeither be diffuse diffuse oror specularspecular..

Reflections off flat Reflections off flat surfaces follow 2 surfaces follow 2 simple rules:simple rules: angle in angle in ((incidenceincidence) ) equals angle outequals angle out ((reflectionreflection))

angles angles measured from measured from the surfacethe surface “normal”.“normal”.

ReflectionReflection

Using the basic rules of reflection, Using the basic rules of reflection, we can createwe can create virtual imagesvirtual images..

Virtual images are images formed Virtual images are images formed by light rays that appear to by light rays that appear to intersect.intersect.

ex. Looking in a mirrorex. Looking in a mirror

Image location can be predicted Image location can be predicted withwith “ray diagrams”.“ray diagrams”.



Ray diagram of mirror image (full Ray diagram of mirror image (full length mirror)length mirror)