Understanding Light and the Electromagnetic Spectrum: Properties, Sources, and Types, Papers of Astronomy

Download Understanding Light and the Electromagnetic Spectrum: Properties, Sources, and Types and more Papers Astronomy in PDF only on Docsity! 1 Light PSC 203 Overview
In this section:
What is light?
What is the EM Spectrum?
How is light created?
What can we learn from light? In-class activity
Discuss your answers in groups of 2
Think of as many examples light sources that you can think of.
List as many as you can on your paper.
Hold onto this list until the end of lecture for the rest of the in-class assignment. Light
What is it?
Your thoughts? What is light?
light is an electro-magnetic wave
electric and magnetic fields oscillate
carries energy as it travels What are waves?
If light is a wave we need to understand what a wave is. 2 Waves
all waves have three related properties
speed:
how fast the wave moves
wavelength:
the distance between peaks
frequency:
how often a peak passes by Speed
the speed of light is very fast
c = 300,000,000 m/s = 3 x 108 m/s
c = 671,000,000 mi/hr Wavelength
the distance between peaks
You can see the wavelength of an ocean wave
You can’t “see” the wavelength of light but it works the same way Frequency
how many peaks pass a fixed point during a set amount of time
most commonly measured in Hz (Hertz)
1 Hz = 1 wave peak per second Visible Light
We don’t see the “waves” in light because they are very small
Different wavelengths correspond to different colors
We can see the colors if we use a tool
In-class experiment 5 ??
A photon of which color of light carries the most energy?
a. Red.
b. Yellow.
c. Green.
d. Blue.
e. All photons have the same energy. Appearance
Objects “look” different depending on what type of light is used
Need special tools to see different types of light
We can get new information by looking at different types of light Object in various light Infrared
Shows heat levels
IR goes through dust and smoke X-rays
Emitted only by high energy processes
Can pass through lower density materials Ultraviolet
Emitted by medium-high energy sources
Flowers show highlighted portions near the pollen when viewed in UV (bees see UV light too)
Old bruises on human skin can sometimes be seen in UV but not visible 6 Radio
Emitted by cold hydrogen
Can pass through solid objects (like walls) Types of Spectra
Continuous, emission, absorption
It depends on how the light was generated
So how is light generated? Emission
the release of light from any material
light is a form of energy...
energy has to be transformed into light from some other form
sources are categorized by the original energy Incandescence
“light created from thermal energy”
object radiates its heat as light
Light is radiated at all wavelengths
Spectrum provides information about the temperature Temperature vs brightness
Total amount of light generated depends on temperature
Hotter object -> more light
Cooler object -> less light Temperature vs color
As an object heats, it appears to change color from red to white to blue
Peak wavelength depends on Temperature
T = (3 x 106 K nm)/λm 7 Incandescent examples
People radiate light because they have thermal energy …
Peak wavelength is in infrared
Brightness is fairly low Incandescent examples
Electric stoves radiate light because they have thermal energy …
Peak wavelength is in red orange yellow region of the visible spectrum
Brightness is moderate Incandescent examples
Blow torches radiate light because they have thermal energy …
Peak wavelength is in blue region of the visible spectrum
Brightness is high Other processes
Not all light is generated by heat Atomic Emission
“light created from atomic energy”
atom releases energy as light
Light is radiated at specific wavelengths
Spectrum provides information on the atoms