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)