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7/28/2019 Chapter 1c Introducing Light and Seeing the Wave Nature of Light
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EE 515 Illumination Engineering Design
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Objectives:1. Appreciate the contribution of scientists in the
understanding of the wave nature of light.
2. Describe reflection, refraction, and diffraction oflight
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The Wave Nature of LightVisually evaluated radiant energy
Light is energy
Transmitted by radiationForm of energy to which eye is sensitive
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Sir Isaac Newton Proponent of the corpuscular theory of light.
All hot bodies emit elastic corpuscles, each having the
same, very high velocity and each having a sizedependent upon its color.
Corpuscles are minute particles that traveled instraight lines and could be reflected and refracted.
Also explained diffraction. Could not explain polarization of light.
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Christian Huygens (1670) Dutch astronomer
Described the bending of light as a fundamental
principle of wave motion Every point on an advancing wavefront behaves as a
secondary wavelets which are sent out radially.
The wavefront encountering an obstruction will sent
out a secondary wave in a direction different from thatof the incident wave.
Laws on reflection and refraction could be explainedby wave theory.
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Flowing water with obstructions
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Thomas Young Reinforced Huygens Theory with his famous
experiment on interference
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Jean Bernard Leon Foucalt Resolved the corpuscular and Huygens-Young wave
theory through the Foucalt Pendulum
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James Clerk Maxwell Noted Scottish physicist in his Treatise on Electricity
and Magnetism
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Heinrich Hertz German physicist, produced electromagnetic waves
experimentally in the microwave region of thespectrum.
Showed that they had the properties of light waves
Verified Maxwells theories were indeed valid anduniversally applicable to all electromagnetic radiation
Proved Maxwells inference that the commondenominator in all electromagnetic radiation is thevelocity of light
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Light: spectrum and color
Newton found that the white light from the Sun is composed
of light of different color, or spectrum (1670).
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Youngs Double-Slit Experiment indicated light behaved as a
wave (1801) The alternating black and bright bands appearing on the
screen is analogous to the water waves that pass through abarrier with two openings
Light has wavelike property
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Youngs Double-Slit Experiment indicated light behaved as a
wave (1801) The alternating black and bright bands appearing on the
screen is analogous to the water waves that pass through abarrier with two openings
Light has wavelike property
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The nature of light is electromagnetic radiation
In the 1860s, James ClerkMaxwell succeeded in describing allthe basic properties of electricity and magnetism in fourequations: the Maxwell equations ofelectromagnetism.
Maxwell showed that electric and magnetic field should travelspace in z/.z,
Light is Electromagnetic Radiation
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Light: Wavelength and Frequency
Example
FM radio, e.g., 103.5 MHz (WTOP station) => = 2.90 m
Visible light, e.g., red 700 nm => = 4.29 X 1014 Hz
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Visible light falls in the 400 to
700 nm range
In the order of decreasing
wavelength
Radio waves: 1 m
Microwave: 1 mm
Infrared radiation: 1 m
Visible light: 500 nm
Ultraviolet radiation: 100 nm X-rays: 1 nm
Gamma rays: 10-3 nm
Electromagnetic Spectrum
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A general rule:
The higher an objects temperature, the more intenselythe object emits electromagnetic radiation and theshorter the wavelength at which emits most strongly
Radiation depending on Temperature
The example of heated iron bar.As the temperature increases
The bar glows morebrightly
The color of the bar alsochanges
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A blackbody is a hypotheticalobject that is a perfect absorber ofelectromagnetic radiation at allwavelengths The radiation of a blackbody is
entirely the result of its temperature
A blackbody does not reflect any lightat all
Blackbody curve: the intensitiesof radiation emitted at variouswavelengths by a blackbody at a
given temperature The higher the temperature, the
shorter the peak wavelength
The higher the temperature, thehigher the intensity
Blackbody Radiation
Blackbody curve
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Hot and dense objects act like a blackbody
Stars, which are opaque gas ball, closely approximate the behavior ofblackbodies
The Suns radiation is remarkably close to that from a blackbody at atemperature of 5800 K
Blackbody Radiation
The Sun as a Blackbody
A human body at room temperature
emits most strongly at infrared light
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(Box 5-1, P97) Three Temperature ScalesTemperature in unit of Kelvin is
often used in physicsTK = TC +273TF = 1.8 (TC+32)
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Blackbody Radiation: Wiens Law
Wiens law states that the dominant wavelength atwhich a blackbody emits electromagnetic radiation isinversely proportional to the Kelvin temperature of theobject
For example
The Sun, max = 500 nm T = 5800 K
Human body at 37 degrees Celcius, or 310 Kelvinmax =
9.35 m = 9350 nm
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Blackbody radiation:
Stefan-Boltzmann Law The Stefan-Boltzmann law states that a blackbody radiates
electromagnetic waves with a total energy flux Fdirectly
proportional to the fourth power of the Kelvin temperature
Tof the object:
F= T4
F = energy flux, in joules per square meter of surface per
second = Stefan-Boltzmann constant = 5.67 X 10-8 W m-2 K-4
T = objects temperature, in kelvins
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Assignment: Devise an experiment which will show the following
concepts
1. Reflection
2. Refraction
3. Diffraction
4. Interference
format
http://localhost/var/www/apps/conversion/tmp/scratch_3/Experiments/Format.docxhttp://localhost/var/www/apps/conversion/tmp/scratch_3/Experiments/Format.docx