Light is a wave or electric and magnetic energy
The speed of light is 186,000 mi/s = 300,000 km/s
Energy = hf = hc/f = frequencyh = Planck's constant= wavelength
Highest energy (E)Highest frequency (f)Shortest Wavelength ()
Lowest energyLowest frequency
Longest Wavelength
c = f x
c = speed of light
Atoms are comprised of a nucleus and electrons (in orbits -> would appear as a swarm or cloud)
protons = positive charge; neutrons = no charge; electrons = negative charge
The nucleus is extremely tiny; atoms are empty space!
This atom is blown up a trillion times = 1012 = 1,000,000,000,000
= 4.5 football fields = 450 yards = 1350 feet = ¼ mile
Atoms are defined by atomic number = number of protons
hydrogen = 1; helium = 2; carbon = 6
The number of electrons is equal to the number of protons.
A given atom does not always have the same number of neutrons (or mass). These different “flavors” of a given atoms are called isotopes.
The electron(s) are allowed only in permitted orbits; unlike planets in a solar system.
The locations (sizes), and therefore energies, of these orbits are unique to each atom
The hydrogen atom
Energy is measured in eV, or electron volts
Light (photon) is electromagnetic energy
Since only permitted electron orbits (energies), there are only permitted photon energies that interact with the atom.
The photon energy equals the energy difference of the electron orbits
(not shown)
(true colors)
Energy = 12.8 – 10.2 = 2.6 eV
Just to drive the point home…
Note in right most panel that the electron slipped back down. This is the process of emission.
absorption process
emission process
A solid object emits a continuous spectrum
A “perfect” object emits a blackbody continuous spectrum
The shape and total energy depend upon only one quantity = temperature
LAW 1
Blackbody Radiation
max = 3,000,000
T nanometer
Etotal = constant x T 4 J/s/m2
Etotal = area under BB curve
T = absolute temperature
Absolute temperature measures the internal kinetic energy of an object. This is the energy from all the motions of the atoms.
LAW 2
A heated gas emits a emission spectrum
The spectral lines depend upon the type of atoms.
Each atom has its unique spectral “fingerprint”
LAW 3
A “cool” gas in front of a hot source yields an absorption spectrum
The spectral lines depend upon the type of atoms.
Stars have absorption spectra.
Stellar spectrum showing hydrogen absorption.