Download ELECTROMAGNETIC SPECTRUM

SPECTROSCOPY AND DOPPLER WAVE
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All radiant energy travels through the
vacuum of space in a straight line at the rate
of 300, 000 kilometers.
1 day = 26 billion kilometers.
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Photon
A quantum of visible light. (Quantum –
smallest quantity of energy)
A photon has neither mass nor electrical
charge.
A photon possesses energy and momentum.
A photon can exert pressure on matter.
(Radiation pressure)
Responsible for “pushing” material away
from a comet to produce its tail.
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Spectroscopy – study of the properties of
light that depend on wavelength.
Newton’s study on prism initiated this study.
Also defined as the study of spectra,
especially to determine the chemical
composition of substances and the physical
properties of molecules, ions and atoms.
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Spectroscope
Instrument for studying spectra; an
instrument for dispersing light usually light in
the visible range, into a spectrum in order to
measure it.
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Three types of spectrum:
1. Continuous spectrum
2. Dark-line spectrum
(Absorption spectrum)
3. Bright-line spectrum
(Emission spectrum)
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1. Continuous spectrum
Is produced by an incandescent solid, liquid or
gas under high pressure.
Consists of an uninterrupted band of color.
E.g. Common light bulb
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2. Dark-line spectrum (Absorption
spectrum)
Is produced when “white” light is passed
through a comparatively cool gas under low
pressure.
Gas absorbs selected wave length of light so
the spectrum that is produced appears as a
continuous spectrum, but with a series of
dark lines.
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3. Bright-line spectrum (Emission
spectrum)
It is a series of bright lines of particular
wavelengths, depending on the gas that
produces them.
These bright lines appear in the exact
location as the dark lines that are produced
by this gas in a dark-line spectrum
(absorption).
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Most stars have dark line spectra.
Each element produces a unique set of
spectral lines.
Each spectrum acts as a “finger print” of a
star and is used to identify the element
present.
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Spectrum of a star (sun) explained in an
overly simplified manner:
Central region – high pressure and high
temperature – continuous spectrum.
Outer region – low pressure and low
temperature – dark-line spectrum.
Dark lines in the spectrum are absorbed
light.
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The spectrum of the sun contains thousands
of dark lines.
Over 60 elements have been identified by
matching those lines with those of elements
known on Earth.
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TWO FACTORS CONCERNING A RADIATING
BODY
1. If the temperature of a radiating surface is
increased, the total amount of energy emitted is
increased.
*Stefan Boltzman Law
The energy radiated by a body is directly
proportional to the fourth power of its absolute
temperature.
E.g. Star – Temperature doubled – energy
emitted times 2 raise to 4 (16 times more
energy.)
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TWO FACTORS CONCERNING A
RADIATING BODY
2. As the temperature of an object increases,
a larger proportion of its energy is radiated at
shorter wavelengths.
E.g. Heated Metal rod
Red – longer wavelength – hot
Blue – shorter wavelength – hotter
Red stars – hot
Blue stars - hotter
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Doppler effect
Explained by Christian Doppler in 1842.
change in frequency because of motion: a
perceived change in the frequency of a wave
as the distance between the source and the
observer changes.
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When a light source is moving away, its light
appears redder than it actually is.
The reason for it is that the wavelength is
stretched.
Objects approaching have their wavelength
waves shifted toward blue (shorter
wavelength).
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Case analysis:
If a source of light is approached you at a very
high speed (near the speed of light),
It would appear blue.
If you move with a speed of light the color of
a stationary light source will appear blue.
By using the Doppler effect
It reveals weather Earth is approaching or
receding from a star or another celestial body.
 The amount of shift allows to recalculate the
rate at which the relative movement is
occurring.
 Larger Doppler shifts indicate higher velocities.
 It is generally measured in from dark lines in the
spectra of stars by comparing them with a
standard spectrum produced in the laboratory.
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