chapter 1c introducing light and seeing the wave nature of light

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

chapter 1c introducing light and seeing the wave nature of light

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