Download Electromagnetic Waves Notes

Monday March 2
Tuesday March 3
Unit Question
What do we know about the universe? How do we know it?
Guiding Question /
Learning Target
How do we know what we know about the universe?
Warm-up
What is a mechanical wave?
Disturbance in matter that carries
energy through medium
Agenda
1. TEST
2. Herschel
3. Em Notes
Homework
STUDY GUIDE DUE NOW!
Test!
Turn in Math and any other
missing work for mechanical
waves.
Last Day!
(did you check no-name
folder?)
Study guide due!
Notes and calculators!
NO PHONES WHILE TESTS ARE OUT
Exploring the Visible Spectrum
• The Herschel Experiment
• William Herschel conducted first conducted this experiment in 1800
• He was a famous astronomer that discovered the planet Uranus
• Herschel Experiment Gizmo
• Record the temperatures on your worksheet
Herschel’s Experiment
• Herschel used a prism to create a rainbow.
• He placed thermometers in different parts of
the colors and beyond (where there was no
color), and recorded temperature changes
over time.
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Start. All temperatures in C
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22
1 Minute. All temperatures in C
22
23
25
22
2 Minutes. All temperatures in C
22
24
27
22
3 Minutes. All temperatures in C
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24
29
23
4 Minutes. All temperatures in C
24
25
31
24
5 Minutes. All temperatures in C
Change in temp?
• What is difference start to finish?
Herschel Experiment Questions
• What did you notice about your temperature readings? Are there any
trends?
• Where was the highest temperature increase?
• What do you notice about your temperature readings?
• As time increases temp increases
• As you go toward red, temp change increases
• Where was the highest temperature change?
• Beyond red
Herschel Experiment Questions
• What do you think exists beyond the red part of the spectrum?
• The highest temperature is beyond the red light
• There must be some kind of radiation we can’t see!
• This unknown radiation is called Infrared Radiation
• Before Herschel’s experiment scientists did not know about other
types of radiation
Stars and galaxies don’t emit only visible light. The
images below show the same region in space but
with a detector for different EM wavelengths.
These pictures
are of the crab
nebula, the
remnants of a
an exploded
star.
Light, Waves and
the Electromagnetic spectrum
Waves… a review
• Most waves are either longitudinal or transverse.
• But all electromagnetic waves are transverse.
Electromagnetic Waves
• Also known as EM waves
• Produced by the movement of electrically charged particles
• Can travel in a “vacuum”
• They do NOT need a medium
• Travel at the speed of
light = 300,000 km/s
Wave-particle Duality
• Light can behave like a wave or like a particle
• A “particle” of light is called a photon.
Electromagnetic Spectrum
The electromagnetic spectrum represents the range of
energy from low energy radio waves with long
wavelengths up to high energy gamma waves with
small wavelengths.
The longer the wavelength, the less the energy.
lowest
energy
Highest
Energy
Visible light is a small portion of this spectrum.
RedOrangeYellowGreenBlueIndigoViolet
ROY G BIV
Astronomers Study Light
• Light is made up of different colors
• Color Vision (web)
• Color Vision (local)
• What happens to the light that enters the prism?
• Do all the colors bend the same way?
• Does the light get bent only once?
The Visible Spectrum
Different Colors of Light
• All light travels at the same speed regardless of its color.
• 186,000 miles per second.
• That’s the length of your ruler in 1 nanosecond!
• The Sun emits most of its
electromagnetic energy in
the visible light part of the
spectrum— our eyes have
evolved to take advantage of
the available “VISIBLE” light.
• Visible light is the only EM
wave that our eyes can
detect.
• From R-L: The same flower with human vision,
only UV vision (bright = UV), simulated bee vision
(UV+G+B), simulated bird vision (tetrachromatcic:
UV+R+G+B). (Photos: (c) Dr Klaus Schmitt,
Weinheim, Germany, uvir.eu )
• Infra red image of a mouse – snakes can detect infra
red (heat) that humans cannot. Most IR images are
false-color to identify areas that are warmer (red) and
cooler (blue/green)
• IR is also part of thermal-imaging night vision
technologies.