WHAT IS LIGHT

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Light
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• CHAPTER 10

Light Reflection and
Refraction
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Part 1

• What is light?
• History of light
• Light wave theory
• Light corpuscular theory
• Electromagnetic theory of light
• Quantum theory of light
• Electromagnetic Spectrum
• Dual nature of light
• How is light produce?

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What is light? Light is defined as the
electromagnetic radiation with wavelengths
between 380 and 750 nm which is visible to the
human eye.
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Historical background of Light

• Huygens Wave Theory of light (1678)
• Newton Corpuscular (particle) Theory (1704)
• Maxwell Electromagnetic Theory (1873)
• Plancks Quantum Theory (1900)

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Huygens Wave Theory of light

• Huygens believed in the wave-like nature of light
• and considered it to propagate as small spherical
  waves
• that add up to form a wavefront that afterwards
  acts as a
• source for new secondary waves.

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Corpuscular (particle) Theory

• Isaac Newton's perform prism experiments .
• He believed that light traveled as a shower of
  particles, each proceeding in a straight line
  until it was refracted, absorbed, reflected,
  diffracted or disturbed in some other manner.

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Page 160 Electromagnetic Theory
(Maxwell)
light consists of electromagnetic oscillations
perpendicular to the direction of travel of the
wave motion.
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Page 160
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Plancks Quantum Theory

• Energy of the EM radiation is quantized
  (Discrete)
• energy of light is proportional to the frequency

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Quantum Based numerical

• Calculate the energy of a photon of radiation
  that has a wavelength of 3.3 µm.
• Solution 2
• Ehc?6.62610-34Js2.998108ms-13.310-6m6.01
  0-20J

alculate the energy of a photon of radiation
whose frequency is 5.0010 14Hz. Solution
1 Ehf6.62610-34Js5.001014s-13.3110-19J The
energy is 3.3110-19J.
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Electro magnetic spectrum
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Releasing of photon
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Page 160
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Faster than light travel???

• According to Einsteins general theory of
  relativity, as an object moves faster, its mass
  increases, while its length contracts. At the
  speed of light, such an object has an infinite
  mass, while its length is zero an
  impossibility. Thus, no object can reach the
  speed of light.

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