Principle(s) Investigated: Chemical Elements, Atomic Structure, Wave Characteristics,
Electromagnetic Radiation, Light Characteristics, Kirchkoff’s Law’s, Emission
spectra, Continuous Spectra, Absorption Spectra
Earth Science 1.e Students know the Sun is a typical star and
is powered by nuclear reactions, primarily the fusion of hydrogen to form
Chemistry 4.f Students
know there is no temperature lower than 0 Kelvin.
Chemistry 1. J Students
know that spectral lines are the result of transitions of electrons between
energy levels and that these lines correspond to photons with a frequency related to the
energy spacing between levels by using Planck's relationship (E = hv).
Physics 4.e Students
know radio waves, light, and X-rays are different wavelength bands in the
spectrum of electromagnetic waves whose speed in a vacuum is approximately
3×108 m/s (186,000 miles/second).
Physics 4.f Students know how to identify
the characteristic properties of waves: interference (beats), diffraction,
refraction, Doppler effect, and polarization.
paperwork, cutouts of absorption spectra for several elements, 3 unknown star
Procedure: Using the
recently gained knowledge of absorption and emission spectra the students
analyze three unknown stars’ absorption spectra by comparing several elements’
spectra and determining which elements are contained in the star based on identical
Student prior knowledge: Basic understanding of atomic
structure regarding electron energy levels, basic understanding of light and
electromagnetic radiation, basic understanding of wave characteristics,
absorption spectra, emission spectra, continuous spectra, black body
Light and Electromagnetic Radiation:
radiation is energy in the form of a wave.
Light is the visible part of the EMR spectrum. When light travels through a prism, it is
split and changes direction due to refraction. Most objects we see have reflected light –
if we turn off the lights we can’t see them.
Glowing objects are emitting light.
If you turn off the lights you still see them glow. All objects emit
light, but we only see them if they’re hot enough.
The light from a star is usually concentrated in a rather
narrow range of wavelengths.
The spectrum of a star’s light is approximately a thermal
spectrum called a black body spectrum.
A perfect black body emitter would not reflect any radiation.
Thus the name “black body”.
Two characteristics of black body radiation are (1) it is a continuous
spectrum (at least some radiation at every wavelength) and (2) the wavelength
of maximum emission depends on the body’s temperature.
Three Types of Spectra: Continuous, Emission, and Absorption:
The continuous spectrum:
At least some radiation at every wavelength – no absorption or
Solids – hot filament of an electric light
Liquids – molten iron
Gas – inside stars
When electrons are pushed by a
photon to a higher energy level, then fall back down, they emit a photon. The wavelength of the photon is determined
by the difference in energy of the two states. These emitted photons form the elements
emission spectra. Each element has a unique
Hydrogen emission spectra
Iron emission spectra
When light from a glowing object
(black body radiator) passes through a cooler gas which absorbs some of the
wavelengths (specific photons that cause that particular elements electron to
jump to an excited energy level).
The elements of the cooler gas absorb exactly the same wavelengths they would
emit if they were in the form of a glowing gas. Scientists can determine what elements are
in the cooler gas by analyzing the absorption lines.
Kirchhoff’s Laws of Radiation
1 - A solid, liquid, or dense gas excited to emit light will
radiate at all wavelengths and thus produce a continuous spectrum.
2 - A low-density
gas excited to emit light will do so at specific wavelengths and thus produce
an emission spectrum.
3 - If light
comprising a continuous spectrum passes through a cool, low-density gas, the
result will be an absorption spectrum.
4. Inner, dense
layers of a star produce a continuous (blackbody) spectrum. Cooler surface layers absorb light at
specific frequencies. Spectra of
stars are absorption spectra.
In basic terms, we
can look at starlight and, using the unique emission spectra for elements, determine
which elements are present in the star by the fact that they absorb the exact
same pattern as they emit, and we can use these patters as a key.
Questions & Answers:
are the emission spectra and absorption spectra patters identical (except in
the opposite manner)? Because they
are both related to the element either absorbing energy (a photon) and
electrons jumping to a higher energy level or releasing energy (the photon)
after returning from an excited state.
The emission spectra shows the presence of the photon emitted, the
absorption spectra shows the absence of the photo absorbed.
the elements we are identifying in the photosphere or the core of the star? They are in the photosphere which is
the “cooler gas” that is absorbing the photons from the inner core into the
does the intensity of light increase dramatically with only a slight change
in temperature (see graph with Black Body Radiation)? Because it follows the inverse square law.
1 – Neon sign is an
example of electrons emitting light in an excited state
2 – Hot metalwork from
a blacksmith. The
yellow-orange glow is the visible part of the thermal radiation emitted due to the high temperature.
– Why the sky is blue. Rayleigh
scattering is the elastic scattering of light or other electromagnetic radiation
by particles much smaller than the wavelength of the light. Rayleigh
scattering of sunlight in the atmosphere causes diffuse sky radiation which
is the reason for the blue color of the sky and the yellow tone of the sun
Include a photograph of you or students performing the
experiment/demonstration, and a close-up, easy to interpret photograph of the
activity --these can be included later.
Videos: Include links to videos posted on the web
that relate to your activity. These can be videos you have made or ones
others have made.