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Light and the Electromagnetic Spectrum

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Light and the Electromagnetic Spectrum ... The Electromagnetic Spectrum The electromagnetic spectrum represents the range of energy from low energy, ... – PowerPoint PPT presentation

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Title: Light and the Electromagnetic Spectrum


1
Light and the Electromagnetic Spectrum
2
Light Phenomenon
  • Isaac Newton (1642-1727) believed light consisted
    of particles
  • By 1900 most scientists believed that light
    behaved as a wave.

3
The Electromagnetic Spectrum
  • The electromagnetic spectrum represents the
    range of energy from low energy, low frequency
    radio waves with long wavelengths up to high
    energy, high frequency gamma waves with small
    wavelengths.

4
  • Visible light is a small portion of this
    spectrum. This is the only part of this energy
    range that our eyes can detect. What we see is a
    rainbow of colors.
  • RedOrangeYellowGreenBlueIndigoViolet
  • ROY G BIV

5
Frequency Ranges
  • Wavelengths
  • 104 101 1 10-2 10-5 10-6 10-8 10-10
    10-12
  • Frequencies (cycles per sec)
  • 3 x 106 3 x 1010 3 x 1014 3 x 1016
    3 x1018 3 x10 22

6
Frequency Ranges of Visible Light
  • Red light has a frequency of roughly
  • 4.3 1014 Hz, and a wavelength of about 7.0
    107 m (700nm).
  • Violet light, at the other end of the visible
    range, has nearly double the frequency7.5 1014
    Hzand (since the speed of light is the same in
    either case) just over half the wavelength
  • 4.0 107 m (400nm).

7
  • The radiation to which our eyes are most
    sensitive has a wavelength near the middle of
    this range, at about
  • 5.5 x 10-7m (550 nm), in the yellow-green region
    of the spectrum.

8
  • It is no coincidence that this wavelength falls
    within the range of wavelengths at which the Sun
    emits most of its electromagnetic energyour eyes
    have evolved to take greatest advantage of the
    available light.

9
C f?
  • The frequency (f) of a wave is the number of
    waves to cross a point in 1 second (units are
    Hertz cycles/sec or sec-1)
  • ? is the wavelength- the distance from crest to
    crest on a wave

10
  • The product of wavelength and frequency always
    equals the speed of light.
  • C f?
  • Why does this make sense?
  • NOTE
  • c is a constant value 3.00 x 108 m/s

11
PROBLEMS
  • Calculate the wavelength of yellow light emitted
    from a sodium lamp if the frequency is
  • 5.10 x 1014 Hz (5.10 x 1014 s-1)
  • List the known info List the unknown
  • c 3.00 x 1010 cm/s wavelength (?) ? cm
  • Frequency (f) 5.10 x 1014 s-1
  • C f? ? c
  • f
  • ? 3.00 x 1010 cm/s 5.88 x 10-5 cm
  • 5.10 x 1014 s-1

12
YOUR TURN
  • 1- What is the wavelength of radiation with a
    frequency of 1.50 x 1013 s-1?
  • 2- What frequency is radiation with a wavelength
    of 5.00 x 10-6 cm? In what region of the
    electromagnetic spectrum is this radiation?
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