Ideas for Web Projects

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Ideas for Web Projects

• Biography of any scientist mentioned in the book
• High-energy Radiation (UV, X-ray, ?-ray)
• Noble Gases (properties, use, where can be found)
• Plate Tectonics (the concept, its history, modern
  view)
• The Fate of the Sun
• First Years of the Universe

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Lecture 12

• Electromagnetic Waves

• Types of electromagnetic waves
• Wave properties

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Electromagnetic Waves
A changing magnetic field generates an electric
current ? electromagnetic induction.
J.C.Maxwell proposed that a changing electric
field has an associated magnetic field.
Such a combined effect results in existence of
electromagnetic waves, which can travel
indefinitely in empty space (vacuum). Electromagne
tic waves travel with the speed of light.
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Light in Everyday Life

• Light is a form of energy, radiative energy

Light has color A prism split light into a
spectrum (rainbow of colors)
Light travels with a speed of c 300,000 km/s
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Rainbow
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Properties of Light
Light behaves as both a particle and a wave
Light particles are called photons, which can be
counted individually. Light is also an
electromagnetic wave
The wavelength is the distance between adjacent
peaks of the electric or magnetic field 1 nm
(nanometer) 109 m 1µm (micron) 106
m The frequency is the number of peaks that pass
by any point each second, measured in cycles per
second or Hertz (Hz). light demo
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Many Forms of Light
The spectrum of light is called the
electromagnetic spectrum
Different portions of the spectrum are called
Gamma rays - the shortest wavelength light X rays
- wavelengths shorter than ultraviolet The
ultraviolet light - beyond the blue end The
visible light - what we see with our eyes The
infrared light - beyond of the red end of
rainbow Radio waves - light with the longest
wavelengths
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Electromagnetic spectrum
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Electromagnetic spectrum
E energy ? frequency h Planck constant
E h ?
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Interaction of Light and Matter

• Emission (atomic spectra)
• Absorption
• Transmission (passing through)
• Reflection (scattering)

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Other Wave Properties
Refraction
Change in a wave direction produced by a change
in speed
Interference
Adding together of 2 or more waves of the same
kind that pass by the same point at the same time
Diffraction
Ability of waves to bend around the edge of an
obstacle Diffraction limit is the largest
resolving power of an optical system.
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Summary
Electromagnetic waves are fluctuations generated
by moving electric charges. Visible light is
only a small portion of the electromagnetic
spectrum. Basic properties of electromagnetic
waves include reflection, refraction,
interference, and diffraction.