Conversations with the Earth Tom Burbine tburbine@framingham

Conversations with the EarthTom Burbinetburbine@framingham.edu

Quiz on Thursday • c = λ x f • E = h * f

Speed of light • Speed of light = 3 x 108 m/s • Usually given with the symbol c • Sped that all massless particles and waves travel

For light • c = wavelength x frequency • In vacuum, speed of light stays the same • So if wavelength goes up • Frequency does down • f = frequency • λ = wavelength • c = λ x f

Calculations • c = λ x f • So if the wavelength is 1 x 10-12 m • 3 x 108 m/s = 1 x 10-12 m * f • f = 3 x 108 m/s/1 x 10-12 m • f = 3 x 1020 s-1 = 3 x 1020 Hz

Calculations • c = λ x f • So if the frequency is 1 x 1015 Hz • 3 x 108 m/s = λ * 1 x 1015 Hz • λ = 3 x 108 m/s/1 x 1015 Hz • λ = 3 x 10-7 m

Energy of light • Energy is directly proportional to the frequency • E = h * f • h = Planck’s constant = 6.626 x 10-34 J∙s • since f = c/λ • Energy is inversely proportional to the wavelength • E = hc/λ

Higher the frequency, Higher the energy of the photon Higher the wavelength, Lower the energy of the photon

Calculations • What is the energy of a radio wave with a frequency of 1 x 107 Hz? • E = h * f • h = Planck’s constant = 6.626 x 10-34 J∙s • E = 6.626 x 10-34 J∙s * 1 x 107 • E = 6.626 x 10-27 J

Calculations • What is the energy of a gamma ray photon with wavelength of 1 x 10-15 m • E = hc/λ • h = Planck’s constant = 6.626 x 10-34 J∙s • E = 6.626 x 10-34 J∙s * 3 x 108 m/s / 1 x 10-15 m • E = 1.99 x 10-10 J

So why are some types of radiation dangerous? • Higher the energy, the farther the photons can penetrate • So gamma and X-rays can pass much more easily into your body • These high-energy photons can ionize atoms in cells • Ionization means removes electrons from an atom

More dangerous

http://www.arpansa.gov.au/images/basics/emr.jpg

ROYGBIV • ROYGBIV • Red – long wavelength • Violet – short wavelength

Any Questions?

Conversations with the Earth Tom Burbine tburbine@framingham