Download Electromagnetic Induction and Electromagnetic Waves

Electromagnetic Induction and
Electromagnetic Waves
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
Learning Objectives:
 Identify circumstances under which changing
magnetic fields lead to induced currents
 Relate Lenz’s law and Faraday’s law to the
direction and size of induced currents
 Apply wave and photon models to the
electromagnetic spectrum
 Discuss the properties of different types of
electromagnetic waves
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 Electromagnetic Induction -Lab
Magnetic Flux
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Lenz’s Law
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Faraday’s Law - Lab
A changing magnetic
field induces an
electric field.
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A changing electric field
induces a magnetic
field.
Electromagnetic Waves
 The f is determined by the
oscillating frequency of
source charges.
 Magnitudes of E and B are
in a definite, constant ratio:
E=cB
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Electromagnetic Waves
 EM waves were predicted and their properties studied
theoretically before they were produced in the lab.
 We have seen that I→B and changing B→E-field
Contributors
 Maxwell, James Clark (1831-1879)
- symmetry between E and B
- E and B acting together → an EM wave that travels,
in a vacuum, at ___________________
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 Hertz, Heinrich (1857-1894)
- first production and observation of EM waves in lab
- LC (inductor & capacitor) circuit used to generate an AC
- found that energy could be transferred from this circuit
to a similar circuit several meters away
- transferred energy exhibited known wave behavior
(reflection, refraction, interference, diffraction, and
can be polarized!
 Marconi (1874-1937)
- first practical application of experimental results →
communication without wires
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Polarization - Lab
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Intensity of an Electromagnetic Wave
 The intensity of a plane wave (e.g. laser beam) does not
change with distance.
 If EM waves are emitted uniformly in all directions, then
I = Psource
4πr2
Example 25.7 Electric and magnetic fields of a cell phone!
Intensity depends on amplitudes of oscillating E and B fields.
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The Electromagnetic Spectrum
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The Photon Model of Electromagnetic Waves
Basic Postulates:
 EM waves consist of mass-less units called
photons.
 Each photon has energy
Ephoton  hf
where f is frequency of the wave and h is a
universal constant called Planck’s constant.
h  6.63 10 J  s
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 Superposition of a large number of photons
has the characteristics of a continuous
electromagnetic wave.
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Thermal Emission Spectrum
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Hunting with Thermal Radiation
Seeing Infrared!
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Summary
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Summary
© 2010 Pearson Education, Inc.