Electromagnetic Waves

1
Electromagnetic Waves

• Maxwells Equations
• Plane waves
• Polarization

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Electromagnetic Waves
Chapter 34 Read Sections 1, 5, 6, 7, 8 Read
Sections 3, 4 lightly Dont read section 2
3
Reading Questions
Maxwells equations are a set of how many
equations?
1. Two 2. Three 3. Four 4. Five 5. Six
4
Reading Questions
Maxwells equations are a set of how many
equations?
1. Two 2. Three 3. Four 4. Five 5. Six
5
Reading Questions
Experimenter A creates a magnetic field in the
laboratory. Experimenter B moves relative to A.
Experimenter B sees
1. just the same magnetic field. 2. a magnetic
field of different strength. 3. a magnetic field
pointing the opposite direction. 4. just an
electric field. 5. both a magnetic and an
electric field.
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Electromagnetic Waves

• For the past five or six weeks we have been
  studying Electrostatics and Magnetostatics. We
  were able to study electrostatics without
  worrying about magnetism. They both were
  independent of the other. As you will recall the
  theory is called Electromagnetic Theory. Thus,
  the two must be related or interconnected. We
  got a feel for this when we studied
  electromagnetic induction. There we saw that a
  changing magnetic field could create an electric
  field. Now we will find out that the reverse is
  also true. A changing electric field creates a
  magnetic field.

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Electromagnetic Waves
relativity
Does Bill measure a magnetic field? Does Sharon
measure a magnetic field?
8
Reading Questions
Experimenter A creates a magnetic field in the
laboratory. Experimenter B moves relative to A.
Experimenter B sees
1. just the same magnetic field. 2. a magnetic
field of different strength. 3. a magnetic field
pointing the opposite direction. 4. just an
electric field. 5. both a magnetic and an
electric field.
9
Reading Questions
Experimenter A creates a magnetic field in the
laboratory. Experimenter B moves relative to A.
Experimenter B sees
1. just the same magnetic field. 2. a magnetic
field of different strength. 3. a magnetic field
pointing the opposite direction. 4. just an
electric field. 5. both a magnetic and an
electric field.
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Electromagnetic Waves

• Maxwells Equations so far

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Electromagnetic Waves

• Displacement Current

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Electromagnetic Waves

• Displacement Current

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Electromagnetic Waves

• Displacement Current

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Electromagnetic Waves

• Displacement Current

15
Electromagnetic Waves

• Maxwells Equations

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Electromagnetic Waves

• Maxwells Equations in free space

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Student Workbook
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Student Workbook
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Student Workbook
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Electromagnetic Waves

• Properties of Electromagnetic Waves
• What is the relationship Maxwell found for the
  speed of electromagnetic waves?
• What is the ratio of the electric field to the
  magnetic field?

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Electromagnetic Waves

• Properties of Electromagnetic Waves
• Below is a drawing of a plane electromagnetic
  wave. Discuss this in your group and make sure
  everyone understands the figure.

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Electromagnetic Waves

• Properties of Electromagnetic Wave

• What is the average energy for an electromagnetic
  wave?
• What is the average power for an electromagnetic
  wave?
• Does an electromagnetic wave have momentum?

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Electromagnetic Waves

• Electromagnetic Spectrum

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Electromagnetic Waves

• Pictures of different types of radiation

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Electromagnetic Waves

• Pictures of different types of radiation

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Electromagnetic Waves

• Mark the following on the figure.
• 1. My favorite radio station KISS 108 MHz (Not
  really, it is WCRB 105.9).
• What is the wavelength?
• 2. Where is the color red?
• What is the wavelength and frequency?
• 3. My dentists uses X-rays (0.8 nm) to check my
  teeth.
• What is the frequency?
• 4. When I was at MIT I used X band (9 GHz)
  microwaves to study superconductivity.
• What is the wavelength?

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Student Workbook
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Student Workbook
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Student Workbook
30
Class Questions
An electromagnetic wave is traveling in the
positive y-direction. The electric field at one
instant of time is shown at one position. The
magnetic field at this position points
1. In the positive x-direction. 2. In the
negative x-direction. 3. In the positive
y-direction. 4. In the negative y-direction. 5.
Away from the origin.
31
Class Questions
An electromagnetic wave is traveling in the
positive y-direction. The electric field at one
instant of time is shown at one position. The
magnetic field at this position points
1. In the positive x-direction. 2. In the
negative x-direction. 3. In the positive
y-direction. 4. In the negative y-direction. 5.
Away from the origin.
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Electromagnetic Waves

• Radiation Source

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Electromagnetic Waves

• Radiation Source

34
Electromagnetic Waves

• Polarization

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Electromagnetic Waves

• Polarization

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Electromagnetic Waves

• Polarization

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Electromagnetic Waves

• Polarization Two Examples

Mechanical stress
Digital displays
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Student Workbook
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Student Workbook
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Student Workbook
41
Class Questions
Unpolarized light of equal intensity is incident
on four pairs of polarizing filters. Rank in
order, from largest to smallest, the intensities
Ia to Id transmitted through the second polarizer
of each pair.
1. Ia Id gt Ib Ic 2. Ib Ic gt Ia Id 3.
Ib Ic gt Ia gt Id 4. Id gt Ia gt Ib gt Ic 5. Id
gt Ia gt Ib Ic
42
Class Questions
Unpolarized light of equal intensity is incident
on four pairs of polarizing filters. Rank in
order, from largest to smallest, the intensities
Ia to Id transmitted through the second polarizer
of each pair.
1. Ia Id gt Ib Ic 2. Ib Ic gt Ia Id 3.
Ib Ic gt Ia gt Id 4. Id gt Ia gt Ib gt Ic 5. Id
gt Ia gt Ib Ic
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Class Questions
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Electromagnetic Waves

• More pictures