PHYSICS - Chapter 16

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PHYSICS - Chapter 16

• SOUTHERN BOONE COUNTY HIGH SCHOOL
• LIGHT
• Bill Palmer

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LIGHT-fundamentals 16.1

• Light is the visible part of the electromagnetic
  spectrum.
• The electromagnetic spectrum runs from long Radio
  and TV waves to short x-rays and gamma-rays.
• Light is defined as the electromagnetic rays that
  stimulate the retina of the human eye.

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LIGHT-fundamentals 16.1

• AM waves
• TV Waves and FM Waves
• Microwaves
• Infrared
• Visible Light
• Ultraviolet
• X-Rays
• Gamma Rays

TYPES OF ELECTROMAGNETIC WAVES
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LIGHT-fundamentals 16.1
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LIGHT-fundamentals 16.1
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LIGHT-fundamentals 16.1

• Electromagnetic waves have frequency and
  wavelength
• Frequencythe number of oscillations measured in
  hertz
• WavelengthThe shortest distance between points
  where a wave pattern repeats itself (meters)

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LIGHT-fundamentals 16.1
WAVELENGTH
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LIGHT-fundamentals 16.1

• Electromagnetic Waves are measured by their
  wavelength
• Radio waves 1 x 10 4 meters
• Gamma waves 1 x 10 14 meters

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LIGHT-fundamentals 16.1

• Light Wavelengths
• Red 7 x10 7 m
• Violet 4 x 10 7 m

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LIGHT-fundamentals 16.1 Roy G. Biv

• RED
• ORANGE
• YELLOW
• GREEN
• BLUE
• INDIGO
• VIOLET

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LIGHT-fundamentals 16.1

• Light travels in a straight line in a vacuum.
• Ray Model of light describes how light travels in
  a straight line.
• Good for optics but ignores the wave nature of
  light.

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LIGHT-fundamentals 16.1

• Speed of Light-originally thought to be
  instantaneous
• Roemer (Danish) measured speed of light from Io
  (moon of Jupiter)
• Compared time when Io emerged from Jupiters
  orbit
• 14 sec. Difference when Earth was moving toward
  Jupiter then when moving away

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LIGHT-fundamentals 16.1
Ole Roemer
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LIGHT-fundamentals 16.1
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LIGHT-fundamentals 16.1

• Roemer found that speed of light could be
  measured.
• Measurements slightly off by todays standard.
• Michelson measured time it took light to travel
  between two mountains in CA.
• 2.997996 .00004 x 108 m/s
• Today we use 3.00 x 108 m/s as speed of light

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LIGHT-fundamentals 16.1

• Speed of light is is a universal value and is
  represented by c.
• Speed is equal to the product of frequency and
  wavelength
• ? lambda wavelength
• C ?f

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LIGHT-fundamentals 16.1

• What is the frequency of yellow light,
• ? 556 nanometers?
• C ? f
• f c / ?
• F 3.00 x 108 m/s / 556 x 109 m
• .00539 x1017 Hz
• 5.40 x 1014 Hz

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LIGHT-fundamentals 16.1

• Complete Problems 2, 3, 4 and 5 page 376
• Note there are 3.28 ft/m (number 2)
• Note 1 femtosecond 10 15 seconds (3a)
• Answers on page 799

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LIGHT-fundamentals 16.1

• Sources of Light
• Luminous Body emits light waves (sun)
• Illuminated Body reflects light waves (moon)
• Luminous Flux is rate at which a luminous body
  emits light (P)

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LIGHT-fundamentals 16.1

• Typical 100-watt light bulb emits 1750 lm
• Illuminance (E) rate at which light falls on a
  surface
• Measured in lumens / meter2 or lux (lx)

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LIGHT-fundamentals 16.1

• Inverse Square Law If the distance a surface is
  moved from a point of light is doubled, the
  illuminance is reduced by a factor of four.
• This is an inverse square relationship
• This is why a flash in photography effectiveness
  falls off rapidly.

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LIGHT-fundamentals 16.1
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LIGHT-fundamentals 16.1

• Candela (cd) is a measure of the intensity of
  light.
• Describes the amount of light that falls on a 1
  m2 of a sphere 1 m in diameter.
• For a brighter light, you must get closer or use
  a brighter bulb. (well, duh!)

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LIGHT-fundamentals 16.1

• Illuminance E (lux lx)
• E P / 4p d 2
• P luminous flux (lumen - lm)

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LIGHT-fundamentals 16.1

• Q What is the illumination on your desktop if it
  is lighted by a 1750-lm lamp that is 2.5 m above
  your desk?
• A E P / 4p d 2
• 1750 lm / 4 p (2.5 m)2
• 22.3 lm/m2 22.3 lx

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LIGHT-fundamentals 16.1

• Complete problems 6, 7, 9 page 381
• Answers on page 799
• Turn in seven problems(35 pts)

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LIGHT-fundamentals 16.2

• Transparent-Transmit light waves w/o distortion
• Translucent-Transmit light waves w/ distortion
• Opaque-Does not transmit light

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LIGHT-fundamentals 16.2

• Color
• Spectrum-ordered arrangement of colors from
  violet to red (Newton)

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LIGHT-fundamentals 16.2

• Color by addition-making white light by adding
  the correct amounts of red, green, and blue light
  (color TV tube)
• Red, Green, and Blue are the PRIMARY Colors of
  light

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LIGHT-fundamentals 16.2
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LIGHT-fundamentals 16.2

• Red Green Yellow
• Blue Green Cyan
• Red Blue Magenta
• Yellow, Cyan, and Magenta are the secondary colors

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LIGHT-fundamentals 16.2
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LIGHT-fundamentals 16.2

• Yellow Blue White
• So, Yellow is Complimentary to Blue
• Cyan and Red are Complimentary
• Magenta and Green are Complimentary

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LIGHT-fundamentals 16.2

• Dyesabsorb certain wavelengths and reflects
  others.
• If white light hits a tomatoblue and green are
  absorbed and red is reflected.
• Pigments are similar to dyes but are larger
  molecules.

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LIGHT-fundamentals 16.2
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LIGHT-fundamentals 16.2

• Soap Bubbles and oil slicks are thin film.
• Think of spectrum-like colors
• Formed by constructive and destructive
  interference of light waves thin-film
  interference

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LIGHT-fundamentals 16.2
SOAP BUBBLE
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LIGHT-fundamentals 16.2
OIL FILM
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LIGHT-fundamentals 16.2

• Polarized light-only allows waves that are
  vibrating in the same plane to pass through.

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LIGHT-fundamentals 16.2
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Light-Chapter 17

• REFLECTION AND REFRACTION
• Southern Boone County HS
• Bill Palmer

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Light-Chapter 17

• Rainbows
• Look at the following pictures of rainbows and
  see what conclusions you can form.

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Light-Chapter 17

• Rainbows

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Light-Chapter 17

• Rainbows

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Light-Chapter 17

• Rainbows

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Light-Chapter 17

• Did you catch the following
• The sun must be shining for a rainbow.
• There must be rain for a rainbow.
• The sky is brighter inside the rainbow.
• In the secondary rainbow, the order of the colors
  are reversed.
• These occur because the light is reflected and
  refracted to form the rainbow.

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Light-Chapter 17

• REFLECTION-Angle of incidence is equal to the
  angle of reflection.
• A regular reflection comes from a smooth
  mirror-like surface.
• A diffuse reflection comes from a rough surface
  like paper. The irregularities in the paper are
  giant compared to the wavelength of lignt.

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Light-Chapter 17
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Light-Chapter 17

• Refraction-When a beam of light passes from one
  object to an object of a different density.
• If light goes from air to glass at an angle it is
  bent.

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Light-Chapter 17
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Light-Chapter 17

• Snells Law The ratio of the sine of the angle
  of incidence to the sine of the angle of
  refraction is a constant.
• N sine q I / sine qr

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Light-Chapter 17

• Indices of Refraction of various materials have
  been calculated in the lab.
• Vacuum 1.00
• Air 1.0003
• Water 1.33
• Ethanol 1.36
• Crown Glass 1.52
• Quartz 1.54
• Flint Glass 1.61 Chart on page 397

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Light-Chapter 17

• A light beam in air hits a sheet of crown glass
  at an angle of 30.00. At what angle is it
  reflected?
• Known
• qi 30.00
• ni 1.00 (1.0003 rounded to sig fig)
• nr 1.52

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Light-Chapter 17

• ni (sin qi) nr (sin qr)
• sin qr ni / nr (sin qi)
• sin qr (1.00/1.52) (.500)
• sin qr .329
• sin qr 19.20

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Light-Chapter 17

• Problems 1-4, page 400. Work Provided
• Problems 5-8, page 402, Work Provided
• Problems 31-43, page 411-412. Answers Provided.