The Nature of LightThe Nature of Light

Light Can Act Like Waves orLight Can Act Like Waves or

In 1801 Thomas Young an English In 1801 Thomas Young an English scientist did an experiment.scientist did an experiment.– Double slit experimentDouble slit experiment

Passed a beam of light through two narrow Passed a beam of light through two narrow openings and projected it onto a screen.openings and projected it onto a screen.

He found the light produced a striped pattern He found the light produced a striped pattern which meant the light was constructively and which meant the light was constructively and destructively interfering.destructively interfering.

This meant that light is composed of waves.This meant that light is composed of waves.

But Light can Also Behave like a But Light can Also Behave like a ParticleParticle

Other observations indicated that light can also Other observations indicated that light can also act like a particle:act like a particle:– When light hits metal it knocks electrons off the When light hits metal it knocks electrons off the

surface.surface.– They found that red light cannot knock electrons off They found that red light cannot knock electrons off

metal no matter how bright it is.metal no matter how bright it is.– If light were a wave then the brighter light should have If light were a wave then the brighter light should have

more energy.more energy.– PhotonsPhotons , light particles contain certain amounts of , light particles contain certain amounts of

energy based on the frequency and wavelength of energy based on the frequency and wavelength of light.light.

– Blue light has a higher frequency and shorter wavelength thus Blue light has a higher frequency and shorter wavelength thus contains more energy than red light.contains more energy than red light.

Light Energy is Proportional to Light Energy is Proportional to FrequencyFrequency

The higher the frequency of light the more The higher the frequency of light the more energy.energy.The speed of light depends on the medium The speed of light depends on the medium it is traveling through.it is traveling through.

– Light travels the fastest through a vacuum.Light travels the fastest through a vacuum.3.0 x 103.0 x 1088 m/s m/s

Light slows down in denser mediums.Light slows down in denser mediums.

The Brightness of Light Depends The Brightness of Light Depends on Intensityon Intensity

IntensityIntensity– The quantity of light illuminating a surface.The quantity of light illuminating a surface.– Depends on the amount of light passing Depends on the amount of light passing

through a certain area or space.through a certain area or space.– Light spreads out in spherical wave fronts.Light spreads out in spherical wave fronts.– Light is more diffuse further from its source.Light is more diffuse further from its source.

Reflection and ColorReflection and ColorReflectionReflection– When light bounces off a surface.When light bounces off a surface.– Rough surfaces reflect light rays in many directions.Rough surfaces reflect light rays in many directions.

Diffuse reflectionDiffuse reflectionCauses a blurry image or no image.Causes a blurry image or no image.

Incident rayIncident ray– Ray hitting the surfaceRay hitting the surface

Reflected rayReflected ray– Ray bouncing off the surfaceRay bouncing off the surface

NormalNormal– An imaginary line that is perpendicular to the surface the light is An imaginary line that is perpendicular to the surface the light is

reflecting from.reflecting from.Angle of IncidenceAngle of Incidence– Angle between incident ray and the normal.Angle between incident ray and the normal.

Angle of reflectionAngle of reflection– Angle between the reflected ray and the normal.Angle between the reflected ray and the normal.

The angle of incidence equals the angle of reflection.The angle of incidence equals the angle of reflection.

Flat MirrorsFlat Mirrors

Plane mirrors (flat mirrors)Plane mirrors (flat mirrors)– Create virtual imagesCreate virtual images

Images you see from the apparent light path not Images you see from the apparent light path not the actual path.the actual path.

– Images are the same size as the object and Images are the same size as the object and they appear the same distance in the mirror they appear the same distance in the mirror as the object is in front of the mirror.as the object is in front of the mirror.

Curved MirrorsCurved Mirrors

Concave mirrors are curved inwardsConcave mirrors are curved inwards– Create real imagesCreate real images

Real images are produced when light is focused in front of Real images are produced when light is focused in front of the mirror.the mirror.

Can be projected onto a screen.Can be projected onto a screen.

Are usually inverted.Are usually inverted.

– Create virtual images Create virtual images When the object is between the focus and the mirror.When the object is between the focus and the mirror.

The image is larger than the object.The image is larger than the object.

These are magnifying mirrors.These are magnifying mirrors.

Curved MirrorsCurved Mirrors

Convex mirrors are curved outwardsConvex mirrors are curved outwards– Are diverging mirrorsAre diverging mirrors– Create virtual imagesCreate virtual images– Images are always smallerImages are always smaller– Panoramic mirrorsPanoramic mirrors

Security mirrorsSecurity mirrors

Side view mirrors on carsSide view mirrors on cars

Seeing ColorsSeeing ColorsThe frequency and wavelength of light determine The frequency and wavelength of light determine what color you will see.what color you will see.– When you optical receptors perceive a wavelength of When you optical receptors perceive a wavelength of

550 nm you see green light.550 nm you see green light.– The colors that you see are a result of surfaces The colors that you see are a result of surfaces

reflecting various wavelengths of light back to your reflecting various wavelengths of light back to your eyes.eyes.

– White lightWhite lightWhen all of the primary colors are being reflected back to When all of the primary colors are being reflected back to your eyes.your eyes.

– No light (or black)No light (or black)When all of the primary colors are being absorbed and no When all of the primary colors are being absorbed and no light is being reflected back to your eyes.light is being reflected back to your eyes.

Primary Colors

• The primary colors are – Red Blue Green

• Your eyes only have receptors for the frequency of light in these three ranges.

• Every other color you percieve is a combination of these three wavelengths in various proportions.

• Adding any two of these colors gives you the secondary colors or primary pigments

Primary Pigments

• Pigments are substances that absorb light.

• The primary pigments are:– Cyan Magenta Yellow

• These are also known as the subtractive colors.– Adding any of these two colors together give

you back the primary colors.

Refraction of LightRefraction of Light

RefractionRefractionWhen light waves bend in a medium due to the When light waves bend in a medium due to the change in density.change in density.

The angle of refraction is NOT equal to the angle The angle of refraction is NOT equal to the angle of reflection.of reflection.

The angle of incidence will be greater than the The angle of incidence will be greater than the angle of refraction if the medium the light is angle of refraction if the medium the light is traveling into is denser.traveling into is denser.

Refraction

RefractionRefraction

Refraction makes objects appear in Refraction makes objects appear in different positions from where they actually different positions from where they actually are.are.– These are virtual images.These are virtual images.– Refraction due to the atmosphere is known as Refraction due to the atmosphere is known as

a mirage.a mirage.– Heating air near the surface of the Earth on a Heating air near the surface of the Earth on a

hot day causes the air near the ground to be hot day causes the air near the ground to be less dense than the air above it.less dense than the air above it.

Internal ReflectionInternal Reflection

Total internal reflectionTotal internal reflection– Occurs when light is refracted so much that it Occurs when light is refracted so much that it

is reflected back into a substance.is reflected back into a substance.Critical angleCritical angle

– When the angle in which light rays meet the boundaries When the angle in which light rays meet the boundaries between the two mediums is so large that the boundary between the two mediums is so large that the boundary acts like a mirror and reflects all of the light back into the acts like a mirror and reflects all of the light back into the medium.medium.

Internal reflection is used in fiber optic cables.Internal reflection is used in fiber optic cables.

Total Internal Reflection

LensesLenses

A curved piece of glass or plastic that changes A curved piece of glass or plastic that changes the direction of light waves.the direction of light waves.– Light is refracted when it enters glass and then again Light is refracted when it enters glass and then again

when it leaves the glass.when it leaves the glass.– Converging lensesConverging lenses

Bend light inward and focus lightBend light inward and focus lightCreate virtual and real imagesCreate virtual and real imagesAlso called convex lensesAlso called convex lenses

– Diverging lensesDiverging lensesBend light outwardBend light outwardCreate virtual images onlyCreate virtual images onlyAlso called concave lensesAlso called concave lenses

Convex and Concave Lenses

Concave and Convex Lenses

Convex Lens ApplicationConvex Lens Application

MagnificationMagnification– When the image is a different size from actual When the image is a different size from actual

object.object.

MicroscopesMicroscopes

TelescopesTelescopes

Lens of the EyeLens of the Eye

Glasses or contact lensesGlasses or contact lenses

CamerasCameras

Near Sighted and Far SightedNear Sighted and Far Sighted

Near sightednessNear sightedness– Occurs when the eyeball is too long causing Occurs when the eyeball is too long causing

the image to be to far in front of the retina.the image to be to far in front of the retina.Diverging lenses move the image back so that the Diverging lenses move the image back so that the image appears on the retina.image appears on the retina.

Far sightedness Far sightedness – Occurs when the eyeball is to short and the Occurs when the eyeball is to short and the

image appears to far behind the retina. image appears to far behind the retina. – Convex lenses move the image upConvex lenses move the image up

Anatomy of the Human Eye

The Eye Uses a Convex Lens

Nearsightedness

Diverging Lenses Correct Nearsightedness

Farsightedness

Converging Lenses Correct Farsightedness

Dispersion and PrismsDispersion and Prisms

DispersionDispersion– When light is refracted in such a way that it When light is refracted in such a way that it

separates light into its individual color separates light into its individual color components.components.

– Prisms are triangular pieces of glass that Prisms are triangular pieces of glass that bend light.bend light.

The angled surface causes the difference The angled surface causes the difference wavelengths of light to separate because they wavelengths of light to separate because they bend at different angles.bend at different angles.Water droplets act like prisms and create Water droplets act like prisms and create rainbows.rainbows.