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The Nature of Light
Anatomy of a wave
What is a photon?
A particle representing a quantum of light
Carries energy proportional to the
radiation frequency
Has zero rest mass
Anatomy of a wave
Amplitude – Distance from peaks to middle of wave
Crest – Top of wave
Trough – Bottom of wave
Wavelength (m) – Distance between crests
Equal to one full cycle of the wave
Frequency (1/s or s-1) – How many wave cycles pass through a given point in a
time interval
Wave speed (how fast its going) = wavelength x frequency
V = λ x f
Speed of light (c) = 3.00 x 108 m/s C = λ x f
Depends on the medium it is traveling through
Anatomy of a wave
Rarefaction –
Stretching of the wave
Compression –
Shortening of the wave
Energy of a wave
ALL WAVES transport energy as they travel
Total Energy – ½spring constant x amplitude squared
E = ½k x A2
This means for a wave caused by simple harmonic motion, that
every particle in the wave will have the same total energy
This tells us that a waves total energy is proportional to the
amplitude squared
Therefore, if you double the waves amplitude, you get 4x the
energy
If you triple the amplitude, you get 9 times the energy
More wave properties
Intensity = power/area
Power = energy/time
Therefore, changing the amplitude of a
wave can change its energy
Intensity is proportional to A2
This can help us figure out how much
damage can be caused by an earthquake
Wave
Interference
Constructive Interference –
When two crests overlap to create on crest with
double the amplitude
Destructive Interference –
One crest and one trough with the same amplitude
overlap and cancel the wave
Wave Property Connections
Longer wavelength = Lower frequency, Lower energy
Shorter wavelength = Higher frequency, Higher energy
Electromagnetic Spectrum
Electromagnetic Spectrum
Electromagnetic Spectrum
Wavelength
Visible Spectrum
White light is refracted (bent) or passed through a prism
Separates the light by color – continuous spectrum
Different colors of light are separated by
their different wavelengths
Color Wavelength (nm)
Red 740-660
Orange 660-620
Yellow 620-580
Green 580-500
Blue 500-415
Violet 415-380
Spectrums
Two types of light spectrums
Continuous
Bright line
States there are mandatory energy levels for atoms
Different atoms have different energy levels, therefore give
off different light combinations
Fingerprint of all atoms, elements, compounds
The Hydrogen Atom
Bohr
Excited State (based off electron placement
around nucleus)
Proposed that an electron moves into an orbit or
higher energy level further from the nucleus when
an atom absorbs energy
Ground State
Electron returns here (home) after being excited
The Hydrogen Spectrum
The Hydrogen Spectrum
Lower energy levels are closer to the
nucleus
Lines converge at higher energies
Energy levels are closer together at higher
energies
Highest energy: n=∞
No longer in atom atom has been ionized
Absorption and Emission
Atoms emit photons
of certain energy and
lines of certain
frequencies
Electrons occupy
specific orbits
Hence, energy of the
atom is quantized
Or approximated
Light as a particle
Energy is released
as electrons fall into
lower energy levels
Energy is released
as ‘light’ from
electromagnetic
radiation
Energy of a photon
is proportional to
frequency
Energy of a photon
E = hf
E = energy of a photon
Units: J = Joule
h = planck’s constant
(6.63x10-34J*s)
f = frequency (1/s or s-1)
Electromagnetic Spectrum
Recap!
What is a photon?
A quantized packet of energy called light
When do atoms emit visible light?
When an electron falls from a higher energy level to
its ground state
What is the relationship between frequency,
wavelength, and energy?
Longer wavelength, lower frequency, lower energy
Shorter wavelength, higher frequency, higher energy
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