Transcript How do we know what stars are made of ?

Sunbeds and stars...
Ionization, excitation and line spectra
Incident
radiation
p
Hydrogen
Atom
e
Electron absorbs
energy and…
Ionisation!
p
e
Is able to completely
escape from the atom
Ionisation!
p
e
Energy = 0
Energy = -13.6eV
• Photons with a minimum energy of 13.6eV are
needed to ionise a hydrogen atom from it’s
ground state.
Lower frequency
radiation
p
Hydrogen
Atom
e
Electron absorbs
radiation and…
Excitation!
p
e
Is only able to move to
a higher energy state
within the atom
The electron in its excited state is unstable
and so it drops back, releasing the energy as
a photon.
-13.6eV
p
-3.6eV
e
One photon with a specific
amount of energy is released
in an electron transition
10eV
Ionisation and excitation
in a fluorescent tube
• High voltage - electrons bombard mercury atoms
• Excitation occurs - unstable electrons fall back
• Ionisation allows the current to flow
-
+
High Voltage
e
e
e
Mercury
e
Argon
High voltage
-
e
e
e
e
Phosphorous coating
Fluorescence
e
e
Argon
+
Spectral transitions in hydrogen
Ionisation
0eV
Electron transitions
Ground state
-13.6eV
Spectroscopy
Looking at the signatures of elements
Intensity
Wavelength of radiation emitted or absorbed