Chapter 14: Light and Reflection The Sombrero Galaxy (nasaimages)
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Transcript of Chapter 14: Light and Reflection The Sombrero Galaxy (nasaimages)
Chapter 14: Light and Reflection
The Sombrero Galaxy
(www.nasaimages.org)
Electromagnetic Waves
• What’s comes to mind when you think of the word light?
• Generally people only think about sources that produce light that is visible to humans
What is light?
• Light waves are electromagnetic waves– Remember that electromagnetic waves do not
need a medium to propagate
• Electromagnetic Wave: A transverse wave consisting of oscillating electric and magnetic fields at right angles to each other.
EM Waves
There’s more than what the eye can see
• Not all light is visible to the human eye
• The complete electromagnetic spectrum contains many different types of radiation
The electromagnetic spectrum
Remembering the Spectrum
• Rabbits Mate In Very Unusual Expensive Gardens• Red Martians Invaded Venus Using X-Ray Guns• From Longest Wavelength to Shortest Wavelength:
Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray, Gamma Ray
Why can’t we see the other parts of the EM spectrum?
• The Sun’s surface is brightest in the portion of the spectrum that is visible to humans
http://apollo.lsc.vsc.edu/classes/met130/notes/chapter2/plank_e_sun.html
Does the Sun emit more than visible light radiation?
X Rays
Infrared
White Light
Microwave/Radio
UltravioletUltraviolet
http://sohowww.nascom.nasa.gov/
The Milky Way
Galaxy M101 Across the Spectrum
All EM waves travel at the speed of light
• Speed of light in a vacuum: c= 3.00 x 108 m/s
• Speed of light = frequency x wavelength
fc
Brightness
• Brightness at any point is the power per unit area at that point (like sound intensity)
• Brightness decreases by the square of the distance from the source– i.e. if you move an object twice as far away
from a light source, one-fourth as much light falls on it
How bright?
• Let’s pretend that a person is looking at a candle that is 1 m away from her. If the candle were move to a distance of 3 m away, how would the brightness change?– The candle would be 1/9 as bright
Section 14.2: Flat Mirrors
• Reflection: The turning back of an electromagnetic wave at the surface of a substance
Enceladus(Moon of Saturn)
• Reflects ~ 99% of EM waves
Iapetus (Moon of Saturn)
• Light regions: Reflect 50-60% of EM Waves
• Dark Regions: Reflect 2-5% of EM Waves
Reflection
• The texture of a surface affects how it reflects light
• Diffuse Reflection: Rough, textured surfaces reflect light in many different directions
• Specular Reflection: Smooth, shiny surfaces (i.e. water) reflect light in one direction
Specular vs Diffuse Reflection
Specular Reflection Diffuse Reflection
•When the book says reflection, it means specular reflection
Basic Reflection
• Angle of Incidence (θ) = Angle of Reflection (θ’)
Angles
Angle of Incidence: (θ) The angle between the incoming light ray and the line perpendicular to the surface
Angle of Reflection: (θ’) The angle between the reflected light ray and the line perpendicular to the surface
Flat Mirrors
• Flat Mirrors are the simplest type of mirror
• When an object is placed in front of a flat mirror, light rays will spread out from the object and reflect from the mirror’s surface
• Virtual Image: An image formed by light rays that only appear to intersect
Flat (Plane) Mirror Images
• The image produced is upright
• The image is the same size as the object (i.e., the magnification is m = 1)
• The image is the same distance from the mirror as the object appears to be (i.e., the image distance = the object distance)
• The image is a virtual image