Transcript Astronomy 1010

Ideas for Web Projects
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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
Lecture 12
Electromagnetic Waves
• Types of electromagnetic waves
• Wave properties
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).
Electromagnetic waves travel with the speed of light.
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
Rainbow
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) = 10–9 m
1μm (micron) = 10–6 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
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
Electromagnetic spectrum
Electromagnetic spectrum
E=h
E = energy  = frequency h = Planck constant
Interaction of Light and Matter
• Emission (atomic spectra)
• Absorption
• Transmission (passing through)
• Reflection (scattering)
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.
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.