Download Slide 1

I. Parts of Light
Light is a form of electromagnetic energy
Acts as a wave that vibrates an electric and magnetic field
Wave Has a wavelength, frequency and amplitude
A. Wavelength λ Length of one complete vibration
amplitude
B. Frequency ν How often the wave vibrates
Measured in cycles/sec
Hertz (Hz)
Wavelength is inversely related to the frequency
s-1
c=λν
c = speed of light (3 x 108 m/s) Almost never changes!
λ = wavelength (m)
ν = frequency in cycles/sec (s-1)
What is the wavelength of light with a frequency
of 1.23 x 1015 s-1?
c=λν
3 x 108 m/s = λ (1.23 x 1015 s-1)
λ = 2.43 x 10-7 m
About 243 nm
Determine the frequency of red light with a
wavelength of 623 nm.
(623 nm = 623 x 10-9 m)
c=λν
3 x 108 m/s = (623 x 10-9 m) v
v = 4.82 x 1014 s-1
C. Visible spectrum
R
O
Y
Long wavelength
Low frequency
G
B
I
V
Short wavelength
High frequency
II. Light as a Particle
A. Max Planck Light is released in small units quanta
Energy of these units is related to frequency of light
E = energy of quantum (J)
E = hv
v = frequency (s-1)
h = Planck’s constant
(6.63 x 10-34 J-s)
What is the energy of a photon with a wavelength of 236 nm?
c=λν
E=hv
3 x 108 m/s = 236 x 10-9 m (v)
E = 6.63 x 10-34 J-s ( 1.27 x 1015)
15
-1
v = 1.27 x 10 sec
E = 8.42 x 10-19 J
B. Photoelectric Effect
When light of a particular wavelength hits a metal,
electrons are released from the metal
eDifferent metals require different wavelengths
Einstein believed that light acted as a particle
photon
The photon is the “packet of energy” described by Planck
Photon gives all of its energy to the metal, (it disappears)
which releases KE as the moving electron
Energy of photon depends on the wavelength of light
Ephoton = hv
C. Matter Waves
It is assumed that light can act as a wave or a particle
Can a particle of matter act as a wave?
De Broglie
Moving matter can be shown to have wave
properties
(Shows diffraction and interference patterns like a wave)
Can determine the wavelength of the moving matter
λ=h
mv
m = mass in grams
v = velocity (m/s)