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Light and Electrons. 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. - PowerPoint PPT Presentation
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I. Parts of LightLight is a form of electromagnetic energyActs as a wave that vibrates an electric and magnetic field
Wave Has a wavelength, frequency and amplitude
A. Wavelength λ
amplitude
B. Frequency ν How often the wave vibrates
Measured in cycles/sec Hertz (Hz) s-1
Wavelength is inversely related to the frequency
Length of one complete vibration
c = λ ν
c = speed of light (3 x 108 m/s)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 = λ ν3 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 = λ ν3 x 108 m/s = (623 x 10-9 m) v v = 4.82 x 1014 s-1
Almost never changesAlmost never changes!
C. Visible spectrum R O Y G B I V
Long wavelengthLow frequency
Short wavelengthHigh frequency
II. Light as a Particle
A. Max Planck Light is released in small units quantaEnergy of these units is related to frequency of light
E = hv E = energy of quantum (J)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 = λ ν3 x 108 m/s = 236 x 10-9 m (v)v = 1.27 x 1015 sec-1
E = h vE = 6.63 x 10-34 J-s ( 1.27 x 1015)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
e-
Different metals require different wavelengths
Einstein believed that light acted as a particle photon
Photon gives all of its energy to the metal, (it disappears) which releases KE as the moving electron
The photon is the “packet of energy” described by Planck
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?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 gramsv = velocity (m/s)