Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine [e-mail]

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Introduction to Physical ScienceMonday,
Wednesday, ThursdayTom Burbinetomburbine_at_astr
o.umass.edu
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Quiz on Thursday

• Magnetism
• Waves
• Light
• c ?f
• E hf
• Electromagnetic spctrum
• Doppler shift

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Wave

• Something that vibrates in space and time
• Light acts as a wave
• Sound acts as a wave

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(No Transcript)
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Frequency

• The number of vibrations per unit time

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Light

• Light is a form of energy

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Light

• These are all forms of light
• Gamma rays
• X-rays
• Ultraviolet light
• Visible light
• Infrared light
• Radio waves

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Light

• Can act as a particle
• Can also act as a wave

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Particle aspect

• Particles called photons stream from the Sun and
  can be blocked by your body

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Photons

• Light is quantized
• Comes in discrete packets called photons

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Wave aspect
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Thomas Young Experiment

• http//micro.magnet.fsu.edu/primer/java/interferen
  ce/doubleslit/

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Characteristics of waves

• velocity wavelength x frequency
• Wavelength distance
• Frequency cycles per second hertz

3 x 108 m/s
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Speed of sound

• Speed of sound 340 m / s

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For light

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

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Calculations

• c ? 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

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Calculations

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

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Energy of light

• Energy is directly proportional to the frequency
• E h f
• h Plancks constant 6.626 x 10-34 J/s
• since f c/?
• Energy is inversely proportional to the
  wavelength
• E hc/?

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

• What is the energy of a radio wave with a
  frequency of 1 x 107 Hz?
• E h f
• h Plancks 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

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Calculations

• What is the energy of a gamma ray photon with
  wavelength of 1 x 10-15 m
• E hc/?
• h Plancks 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

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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 the body
• These high-energy photons can ionize atoms in
  cells
• Ionization means removes electrons from an atom

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More dangerous
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http//www.arpansa.gov.au/images/basics/emr.jpg
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ROYGBIV

• ROYGBIV
• Red long wavelength
• Violet short wavelength

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Doppler Shift

• If a light or sound source moves towards you, the
  wavelength you measure (hear) from the source
  decreases
• Frequency increases
• If a light or sound source moves away from you,
  the wavelength you measure (hear) from the source
  increases
• Frequency decreases

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• http//www.youtube.com/watch?v-t63xYSgmKEfeature
  related

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Doppler Shift
http//www.psi.edu/esquerdo/asp/shifts.jpg
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(No Transcript)
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• http//www.youtube.com/watch?va3RfULw7aAY

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Wavelength
http//www.psi.edu/esquerdo/asp/method.html
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Any Questions?