Transcript electromagnetic waves

Intro to light - Flame Test
• Can be used to identify elements.
• Energy (heat) is used to excite
electrons in an atom.
• Electrons temporarily move from ground
state (where they prefer to be) to
excited state (a high energy level).
• As electron returns to ground state,
atom emits energy in the form of light.
Photon
Gulp!!!
Shake!!
Burp!!
Electromagnetic Radiation
(light)
• Produced by changing electric and magnetic
fields
• Can be thought of as both a particle and a
wave (wave-particle duality)
• Does NOT require a medium
• Transverse
HOMEWORK
Mechanical
waves
Electromagnetic
waves
Read pgs. 500, 532, 533
Electromagnetic Waves
Homework Assignment:
•Read pg. 500, 532, 533
•Make a double bubble map to compare
and contrast electromagnetic waves to
mechanical waves.
Light as a Wave
•
When we treat light as a wave, it has
the properties of any other wave:
1. Wavelength
2. Frequency
3. Speed
•
Speed = Wavelength x Frequency
These properties are related just like
they are with mechanical waves.
What is the formula?
Electromagnetic RADiation
• The Sun is the source of EM radiation
on Earth
• Speed remains the same: all EM waves
travel at the speed of light:
3.00 x
8
10
m/s
Practice Problems
1.
What is the wavelength of an electromagnetic
wave that has a frequency of 4.03x1014 Hz?
2. What is the frequency of an electromagnetic
wave that has a wavelength of 3 m?
Electromagnetic
Spectrum
• When we think of light as a wave, we discover
that electromagnetic radiation (light) can
come in many forms. These forms depend on
the wavelength and frequency of the light.
• Electromagnetic waves of different
frequency/wavelength fall onto different
places on the electromagnetic spectrum.
Electromagnetic
Spectrum
Left to Right: wavelength decreases, frequency increases
Electromagnetic Spectrum
Radio Waves
• Used in radio and television
transmission.
microWaves
• Used in microwave appliances
• Radar waves are also
a form of microwaves
Infared waves
• Show the amount of thermal energy
(heat) a particular object has.
• Heat or Night Vision
Visible Light waves
• Waves our eyes are capable of seeing
R
O
Y
G
B
I
V
Ultraviolet Waves
• First potentially harmful form of EM
radiation
• Overexposure can lead to skin cancer
X-Rays
• Used in the medical field to look inside
the human body
Gamma Rays
• Highest energy form of EM radiation
• Hardest radiation to be protected from
• Used in treatment of cancer (radiation
treatment)
What is giving off radiation?
• By studying and displaying the em
radiation given off by stars, scientists can
determine the chemical composition of
those stars among other things.
Spectrum/Spectra
Spectrum  to made a display out of something
In astronomy, we display radiation using
spectroscopes (bend light to see various
wavelengths being emitted)
Each element produces a set of characteristic
emission lines
•
From spectral lines astronomers can determine not only the element, but
the temperature and density of that element in the star. The spectral line
also can tell us about any magnetic field of the star. The width of the line
can tell us how fast the material is moving. We can learn about winds in
stars from this. If the lines shift back and forth we can learn that the star
may be orbiting another star. We can estimate the mass and size of the star
from this. If the lines grow and fade in strength we can learn about the
physical changes in the star. Spectral information can also tell us about
material around stars. This material may be falling onto the star from a
doughnut-shaped disk around the star called an accretion disk. These disks
often form around a neutron star or black hole. The light from the stuff
between the stars allows astronomers to study the interstellar medium
(ISM). This tells us what type of stuff fills the space between the stars.
Space is not empty! There is lots of gas and dust between the stars.
Spectroscopy is one of the fundamental tools which scientists use to study
the Universe.
Spectra
Discrete
Continuous
A luminous solid or liquid
emits a continuous
spectrum of all
wavelengths. It has no
lines in it.
Emission
When hot gas is
emitted its own
light
Absorbtion
When light from a
brigher source is
shone through it
Signatures of elements
Sun Spectrum