E M Spectrum Snell S Law And Ray Diagrams

WAVES: SOUND & LIGHT

WAVES: SOUND & LIGHT

Waves carry energy from one place to another

Waves carry energy from one place to another

NATURE OF WAVESNATURE OF WAVES

Waves (Def.) – A wave is a disturbance that transfers energy.

Medium – Substance or region through which a wave is transmitted.

Speed of Waves – Depends on the properties of the medium.

Waves (Def.) – A wave is a disturbance that transfers energy.

Medium – Substance or region through which a wave is transmitted.

Speed of Waves – Depends on the properties of the medium.

LIGHT: What Is It?

LIGHT: What Is It?

Light EnergyAtoms

As atoms absorb energy, electrons jump out to a higher energy level.

Electrons release light when falling down to the lower energy level.

Photons - bundles/packets of energy released when the electrons fall.

Light: Stream of Photons

Light EnergyAtoms

As atoms absorb energy, electrons jump out to a higher energy level.

Electrons release light when falling down to the lower energy level.

Photons - bundles/packets of energy released when the electrons fall.

Light: Stream of Photons

© 2000 Microsoft Clip Gallery


Electromagnetic Waves

Electromagnetic Waves

Speed in Vacuum300,000 km/sec186,000 mi/sec

Speed in Other MaterialsSlower in Air, Water, Glass

Speed in Vacuum300,000 km/sec186,000 mi/sec

Speed in Other MaterialsSlower in Air, Water, Glass


Transverse Waves

Transverse Waves

Energy is perpendicular to direction of motion

Moving photon creates electric & magnetic fieldLight has BOTH Electric & Magnetic

fields at right angles!

Energy is perpendicular to direction of motion

Moving photon creates electric & magnetic fieldLight has BOTH Electric & Magnetic

fields at right angles!


Electromagnetic Spectrum





Visible Spectrum – Light we can seeRoy G. Biv – Acronym for Red, Orange,

Yellow, Green, Blue, Indigo, & Violet.Largest to Smallest Wavelength.

Visible Spectrum – Light we can seeRoy G. Biv – Acronym for Red, Orange,

Yellow, Green, Blue, Indigo, & Violet.Largest to Smallest Wavelength.



Invisible SpectrumRadio Waves

Def. – Longest wavelength & lowest frequency.

Uses – Radio & T.V. broadcasting.

Invisible SpectrumRadio Waves

Def. – Longest wavelength & lowest frequency.

Uses – Radio & T.V. broadcasting.


Modulating Radio Waves

Modulating Radio Waves

Modulation - variation of amplitude or frequency when waves are broadcastAM – amplitude modulation

Carries audio for T.V. BroadcastsLonger wavelength so can bend around hills

FM – frequency modulation Carries video for T.V. Broadcasts

Modulation - variation of amplitude or frequency when waves are broadcastAM – amplitude modulation

Carries audio for T.V. BroadcastsLonger wavelength so can bend around hills

FM – frequency modulation Carries video for T.V. Broadcasts


Short Wavelength Microwave

Short Wavelength Microwave

Invisible Spectrum (Cont.)Infrared Rays

Def – Light rays with longer wavelength than red light.

Uses: Cooking, Medicine, T.V. remote controls

Invisible Spectrum (Cont.)Infrared Rays

Def – Light rays with longer wavelength than red light.

Uses: Cooking, Medicine, T.V. remote controls



Invisible spectrum (cont.).Ultraviolet rays.

Def. – EM waves with frequencies slightly higher than visible light

Uses: food processing & hospitals to kill germs’ cells

Helps your body use vitamin D.

Invisible spectrum (cont.).Ultraviolet rays.

Def. – EM waves with frequencies slightly higher than visible light

Uses: food processing & hospitals to kill germs’ cells

Helps your body use vitamin D.



Invisible Spectrum (Cont.)X-Rays

Def. - EM waves that are shorter than UV rays.

Uses: Medicine – Bones absorb x-rays; soft tissue does not.

Lead absorbs X-rays.

Invisible Spectrum (Cont.)X-Rays

Def. - EM waves that are shorter than UV rays.

Uses: Medicine – Bones absorb x-rays; soft tissue does not.

Lead absorbs X-rays.



Invisible spectrum (cont.)Gamma rays

Def. Highest frequency EM waves; Shortest wavelength. They come from outer space.

Uses: cancer treatment.

Invisible spectrum (cont.)Gamma rays

Def. Highest frequency EM waves; Shortest wavelength. They come from outer space.

Uses: cancer treatment.

LIGHT: Particles or Waves?LIGHT: Particles or Waves?

Wave Model of LightExplains most properties of light

Particle Theory of LightPhotoelectric Effect – Photons of

light produce free electrons

Wave Model of LightExplains most properties of light

Particle Theory of LightPhotoelectric Effect – Photons of

light produce free electrons


LIGHT: Refraction of Light

LIGHT: Refraction of Light

Refraction – Bending of light due to a change in speed. Index of Refraction – Amount by which a

material refracts light.Prisms – Glass that bends light. Different

frequencies are bent different amounts & light is broken out into different colors.

Refraction – Bending of light due to a change in speed. Index of Refraction – Amount by which a

material refracts light.Prisms – Glass that bends light. Different

frequencies are bent different amounts & light is broken out into different colors.

Color of LightColor of LightTransparent Objects:

Light transmitted because of no scatteringColor transmitted is color you see. All other

colors are absorbed.Translucent:

Light is scattered and transmitted some.Opaque:

Light is either reflected or absorbed. Color of opaque objects is color it reflects.

Transparent Objects: Light transmitted because of no scatteringColor transmitted is color you see. All other

colors are absorbed.Translucent:

Light is scattered and transmitted some.Opaque:

Light is either reflected or absorbed. Color of opaque objects is color it reflects.


Color of Light (Cont.)

Color of Light (Cont.)

Color of ObjectsWhite light is the presence of ALL the

colors of the visible spectrum.Black objects absorb ALL the colors

and no light is reflected back.

Color of ObjectsWhite light is the presence of ALL the

colors of the visible spectrum.Black objects absorb ALL the colors

and no light is reflected back.


How You SeeHow You See

Retina – Lens refracts light to converge on the

retina. Nerves transmit the imageRods –

Nerve cells in the retina. Very sensitive to light & dark

Cones – Nerve cells help to see light/color

Retina – Lens refracts light to converge on the

retina. Nerves transmit the imageRods –

Nerve cells in the retina. Very sensitive to light & dark

Cones – Nerve cells help to see light/color


Refraction (Cont.)Refraction (Cont.)

Geometry Refresher

A

B

C

parallel lines

given A:

Electrical Component

Magnetic Component

Electromagnetic Wave

In optics ignore magnetic component

Wavelength and Frequency

Wavelength: Distance between adjacent troughs or crests

nm (10-9 m)

Frequency: Number of times cycle repeats per second

f Hz (sec-1)

Speed = Frequency X Wavelength

v = f

Speed of light in vacuum, C = 3 x 108 m/sec

Index of refraction, = nCV

Speed is slower in matter

E.g. glass: = n3 X 10

8

2 X 108 = 1.5

AirNew Medium

Speed = C

Speed = V

medium 1medium 2

n1

n2

angle ofincidence

angle ofrefraction

REFRACTION

Snell’s Law: n1sinn2sin

Snell’s Lawn1 sin = n2 sin

n1 = 1.00

30o

n2 = 1.50

?o

19.47o

Willebrord van Roijen Snell1580 - 1626

Professor of Mathematics University of Leiden, Netherlands

lower n higher n

Ray bends toward normal

Which way do the rays bend in refraction?

higher n lower n

Ray bends away from normal

Atmospheric Refraction and Mirages

Atmospheric Refraction and Mirages

A mirage can be observed when the air above the ground is warmer than the air at higher elevations

The rays in path B are directed toward the ground and then bent by refraction

The observer sees both an upright and an inverted image

A mirage can be observed when the air above the ground is warmer than the air at higher elevations

The rays in path B are directed toward the ground and then bent by refraction

The observer sees both an upright and an inverted image

Reflection and Refraction

refracted ray

reflected ray

n

n’

i r

n’ > n

incident ray

i = r

Light is reflected as well as refracted at surfaces.

Reflection Reflection

Reflection – Bouncing back of light wavesRegular reflection – mirrors smooth

surfaces scatter light very little. Images are clear & exact.

Diffuse reflection – reflected light is scattered due to an irregular surface.

Reflection – Bouncing back of light wavesRegular reflection – mirrors smooth

surfaces scatter light very little. Images are clear & exact.

Diffuse reflection – reflected light is scattered due to an irregular surface.

Reflection VocabularyReflection Vocabulary

Enlarged – Image is larger than actual object.

Reduced –Image is smaller than object.

Upright –Image is right side up.

Inverted – Image is upside down.

Enlarged – Image is larger than actual object.

Reduced –Image is smaller than object.

Upright –Image is right side up.

Inverted – Image is upside down.

Reflection VocabularyReflection VocabularyFocal Point – Point where reflected or

refracted rays meet & image is formedFocal Length – Distance between

center of mirror/lens and focal point

Focal Point – Point where reflected or refracted rays meet & image is formed

Focal Length – Distance between center of mirror/lens and focal point

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

NotationsNotations The distance from the object to the lens is denoted by Do

The distance from the image to the lens is denoted by Di

The lateral magnification of the lens is the ratio of the image height (h ’) to the object height (h)Denoted by M (=h’/h)

The distance from the object to the lens is denoted by Do

The distance from the image to the lens is denoted by Di

The lateral magnification of the lens is the ratio of the image height (h ’) to the object height (h)Denoted by M (=h’/h)



Types of Images for Mirrors and LensesTypes of Images for Mirrors and Lenses

A real image is one in which light actually passes through the image pointReal images can be displayed on screens

A virtual image is one in which the light does not pass through the image pointThe light appears to come (diverge) from

that pointVirtual images cannot be displayed on

screens

A real image is one in which light actually passes through the image pointReal images can be displayed on screens

A virtual image is one in which the light does not pass through the image pointThe light appears to come (diverge) from

that pointVirtual images cannot be displayed on

screens

Flat MirrorFlat Mirror

Simplest possible mirror Properties of the image

can be determined by geometry

One ray starts at P, follows path PQ and reflects back on itself

A second ray follows path PR and reflects according to the Law of Reflection

Simplest possible mirror Properties of the image

can be determined by geometry

One ray starts at P, follows path PQ and reflects back on itself

A second ray follows path PR and reflects according to the Law of Reflection

Di=Do

Properties of the Image Formed by a Flat MirrorProperties of the Image Formed by a Flat Mirror

The image is as far behind the mirror as the object is in frontDi = Do

The image is unmagnified, M=1The image is virtualThe image is upright

It has the same orientation as the objectThere is an apparent left-right reversal

in the image

The image is as far behind the mirror as the object is in frontDi = Do

The image is unmagnified, M=1The image is virtualThe image is upright

It has the same orientation as the objectThere is an apparent left-right reversal

in the image

Application – Day and Night Settings on Car

Mirrors

Application – Day and Night Settings on Car

Mirrors

With the daytime setting, the bright beam of reflected light is directed into the driver’s eyes

With the nighttime setting, the dim beam (D) of reflected light is directed into the driver’s eyes, while the bright beam goes elsewhere

With the daytime setting, the bright beam of reflected light is directed into the driver’s eyes

With the nighttime setting, the dim beam (D) of reflected light is directed into the driver’s eyes, while the bright beam goes elsewhere

Spherical MirrorsSpherical Mirrors

A spherical mirror has the shape of a segment of a sphere

A concave spherical mirror has the silvered surface of the mirror on the inner, or concave, side of the curve

A convex spherical mirror has the silvered surface of the mirror on the outer, or convex, side of the curve

A spherical mirror has the shape of a segment of a sphere

A concave spherical mirror has the silvered surface of the mirror on the inner, or concave, side of the curve

A convex spherical mirror has the silvered surface of the mirror on the outer, or convex, side of the curve

LIGHT & ITS USES: MirrorsLIGHT & ITS USES: Mirrors

Convex MirrorA convex mirror is sometimes

called a diverging mirrorCurves outwardReduces images.

Use: Rear view mirrors, store security…

Convex MirrorA convex mirror is sometimes

called a diverging mirrorCurves outwardReduces images.

Use: Rear view mirrors, store security…

CAUTION! Objects are closer than they appear!

Concave Mirror, Do > FConcave Mirror, Do > F

The image is realThe image is invertedThe image is smaller than the object

The image is realThe image is invertedThe image is smaller than the object

Concave Mirror, Do < FConcave Mirror, Do < F

The image is virtualThe image is uprightThe image is larger than the object

The image is virtualThe image is uprightThe image is larger than the object

Convex MirrorConvex Mirror

The image is virtualThe image is uprightThe image is smaller than the object

The image is virtualThe image is uprightThe image is smaller than the object

Drawing A Ray DiagramDrawing A Ray Diagram To make the ray diagram, you need to know

The position of the object The position of the center of curvature

Three rays are drawn They all start from the same position on the object

The intersection of any two of the rays at a point locates the image The third ray serves as a check of the construction

A ray diagram can be used to determine the position and size of an image

To make the ray diagram, you need to know The position of the object The position of the center of curvature

Three rays are drawn They all start from the same position on the object

The intersection of any two of the rays at a point locates the image The third ray serves as a check of the construction

A ray diagram can be used to determine the position and size of an image



Sign Conventions for Lenses

Sign Conventions for Lenses

Quantity Positive When

Negative When

Object location (Do)

Object is in front of surface

Object is in back of surface

Image location (Di)

Image is in back of surface (real)

Image is in front of surface (virtual)

Image height (h’)

Image is upright

Image is inverted

Focal Length (f)(1/2 Radius of Curvature, C)

Converging Lens

Diverging Lens

Focal Length of a Converging LensFocal Length of a Converging Lens

The parallel rays pass through the lens and converge at the focal point F

The parallel rays can come from the left or right of the lens

f is positive

The parallel rays pass through the lens and converge at the focal point F

The parallel rays can come from the left or right of the lens

f is positive

Focal Length of a Diverging Lens

Focal Length of a Diverging Lens

The parallel rays diverge after passing through the diverging lens

The focal point is the point where the rays appear to have originated

f is negative

The parallel rays diverge after passing through the diverging lens

The focal point is the point where the rays appear to have originated

f is negative

LIGHT & ITS USES: Lenses


Convex Lenses Thicker in the center than edges. Lens that converges (brings together)

light rays. Forms real images and virtual images

depending on position of the object

Convex Lenses Thicker in the center than edges. Lens that converges (brings together)

light rays. Forms real images and virtual images

depending on position of the object



Convex Lenses Ray Tracing

Two rays usually define an imageRay #1: Light ray comes from top of

object; travels parallel to optic axis; bends thru focal point.


Two rays usually define an imageRay #1: Light ray comes from top of

object; travels parallel to optic axis; bends thru focal point.

Focal Point

Lens

Object

© 2000 D. L. Power




Two rays define an imageRay 2: Light ray comes from top of

object & travels through center of lens.


Two rays define an imageRay 2: Light ray comes from top of

object & travels through center of lens.

Ray #1

Ray #2

© 2000 D. L. Power



Concave Lenses – Lens that is thicker at the edges and

thinner in the center. Diverges light rays All images are upright and reduced.

Concave Lenses – Lens that is thicker at the edges and

thinner in the center. Diverges light rays All images are upright and reduced.

© 2000 D. L. Power

How You See

How You See

Near Sighted – Eyeball is too long and image focuses in front of the retina

Far Sighted – Eyeball is too short so image is focused behind the retina.

Near Sighted – Eyeball is too long and image focuses in front of the retina

Far Sighted – Eyeball is too short so image is focused behind the retina.



LIGHT & USES: LensesLIGHT & USES: Lenses

Concave Lenses – Vision – Eye is a convex lens.

Nearsightedness – Concave lenses expand focal lengths

Farsightedness – Convex lenses shortens the focal length.

Concave Lenses – Vision – Eye is a convex lens.

Nearsightedness – Concave lenses expand focal lengths

Farsightedness – Convex lenses shortens the focal length.

LIGHT & USES: Optical Instruments

LIGHT & USES: Optical Instruments

CamerasTelescopesMicroscopes

CamerasTelescopesMicroscopes


© 2000 Microsoft Clip Gallery © 2000 Microsoft Clip Gallery

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E M Spectrum Snell S Law And Ray Diagrams

Education