November 18, 2013
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Transcript of November 18, 2013
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November 18, 2013
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Electromagnetic Radiation
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Objectives
• At the end of class, you will be able to:• List the forms of electromagnetic radiation• Find wavelength or frequency of
electromagnetic radiation
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Waves and Particles
• Particles are solid matter• Waves are movement in matter, like an ocean
wave or a wave at a football game
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Electromagnetic Radiation• Energy that travels through space as a wave
EXAMPLES:• Gamma rays• X-rays• Ultraviolet rays• Visible light• Infrared • Microwaves• Radiowaves
Electromagnetic spectrum
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• In a vacuum all electromagnetic radiation travels at the speed of light.
• This speed is c = 3.0 × 108 m/s
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Wavelength
• Symbol: λ (lambda) • Units: m (meter)• Distance between corresponding points on a
wave
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Frequency
• Symbol: ν (nu)• Units: s-1, Hz, 1/s• Number of waves that pass a point per second
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Each form of light has different wavelength and
frequency, but they all have the SAME SPEED
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• As wavelength ______________, frequency _______________.
• As wavelength ______________, frequency ________________.
increasesdecreases
decreasesincreases
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The big equation for EM radiation:
c = λν
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PRACTICE:• 1. What is the wavelength of electromagnetic radiation
with a frequency of 2.0 × 1015 Hz? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light?
• Use formula: c = λν• Identify known information:
c = 3.0 x 108 m/s ν = 2.0 × 1015 Hz• Plug known information into formula:
3.0 x 108 m/s = λ(2.0 × 1015 Hz)• Solve for λ
λ = (3.0 x 108 m/s)/(2.0 × 1015 Hz) λ = 1.5 × 10-7 m
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Ultraviolet light
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PRACTICE:• 2. What is the frequency of light with a wavelength of
4.5 × 10-7 m? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light?
• Use formula: c = λν• Identify known information:
c = 3.0 x 108 m/s λ = 4.5 × 10-7 m• Plug known information into formula:
3.0 x 108 m/s = (4.5 × 10-7 m) ν• Solve for ν
ν = (3.0 x 108 m/s)/(4.5 × 10-7 m) ν = 6.67 × 1014 Hz
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Visible light – Blue
Visible light – Blue
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PRACTICE:• 3. What is the wavelength of electromagnetic
radiation with a frequency of 5.85 × 1018 Hz? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light?
• Use formula: c = λν• Identify known information:
c= 3.0 x 108 m/s v = 5.85 x 1018 Hz • Plug known information into formula:
3.0 x 108 m/s = λ (5.85 x 1018 s-1)• Solve for ν ν = (3.0 x 108 m/s)/(5.85 x 1018 s-1) = ν = 5.13 x 10-11 m
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Gamma Rays (or X-rays) – The wavelengths overlap sometimes
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PRACTICE:
• 4. What is the frequency of light with a wavelength of 64 cm? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light?
• Hint: make sure all variables are in units of m! • 64 cm | 1m = 0.64 m 100 cm
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PRACTICE:
• 4. What is the frequency of light with a wavelength of 0.64 m? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light?
• Use formula: c = λν• Identify known information:
c= 3.0 x 108 m/s λ = 0.64 m• Plug known information into formula:
3.0 x 108 m/s = (0.64m) ν
• Solve for ν
ν = (3.0 x 108 m/s)/(0.64 m) = ν = 4.69 x 108 Hz
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Radio Waves
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Check:
• What is wavelength?• What is the unit for wavelength?• What is frequency?• What is the unit for frequency?• How can you find one if you know the other?