e m spectrum snell s law and ray diagrams
TRANSCRIPT
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WAVES: SOUND & LIGHT
WAVES: SOUND & LIGHT
Waves carry energy from one place to another
Waves carry energy from one place to another
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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.
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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
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© 2000 Microsoft Clip Gallery
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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
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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!
© 2000 Microsoft Clip Gallery
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Electromagnetic Spectrum
Electromagnetic Spectrum
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Electromagnetic Spectrum
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.
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Electromagnetic Spectrum
Electromagnetic Spectrum
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.
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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
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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
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Electromagnetic Spectrum
Electromagnetic Spectrum
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.
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Electromagnetic Spectrum
Electromagnetic Spectrum
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.
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Electromagnetic Spectrum
Electromagnetic Spectrum
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.
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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
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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.
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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.
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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.
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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
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Refraction (Cont.)Refraction (Cont.)
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Geometry Refresher
A
B
C
parallel lines
given A:
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Electrical Component
Magnetic Component
Electromagnetic Wave
In optics ignore magnetic component
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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
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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
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medium 1medium 2
n1
n2
angle ofincidence
angle ofrefraction
REFRACTION
Snell’s Law: n1sinn2sin
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Snell’s Lawn1 sin = n2 sin
n1 = 1.00
30o
n2 = 1.50
?o
19.47o
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Willebrord van Roijen Snell1580 - 1626
Professor of Mathematics University of Leiden, Netherlands
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lower n higher n
Ray bends toward normal
Which way do the rays bend in refraction?
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higher n lower n
Ray bends away from normal
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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
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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.
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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.
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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.
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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
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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)
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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
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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
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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
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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
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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
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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!
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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
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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
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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
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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
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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
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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
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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
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LIGHT & ITS USES: Lenses
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
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LIGHT & ITS USES: Lenses
LIGHT & ITS USES: Lenses
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.
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.
Focal Point
Lens
Object
© 2000 D. L. Power
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LIGHT & ITS USES: Lenses
LIGHT & ITS USES: Lenses
Convex Lenses Ray Tracing
Two rays define an imageRay 2: Light ray comes from top of
object & travels through center of lens.
Convex Lenses Ray Tracing
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
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LIGHT & ITS USES: Lenses
LIGHT & ITS USES: Lenses
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
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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.
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© 2000 Microsoft Clip Gallery
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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.
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LIGHT & USES: Optical Instruments
LIGHT & USES: Optical Instruments
CamerasTelescopesMicroscopes
CamerasTelescopesMicroscopes
© 2000 Microsoft Clip Gallery
© 2000 Microsoft Clip Gallery © 2000 Microsoft Clip Gallery