Chapter 14/25
Electromagnetic Waves
The Electromagnetic Spectrum
Figure 25-3
The Right-Hand Rule Applied to an Electromagnetic Wave
Figure 25-1
All Accelerating Charges Radiate Electromagnetic
Waves
Receiving Radio Waves - Resonance
Maxwell - Electromagnetic waves
All electromagnet waves travel at the
speed of light in a vacuum
Roses are Red, Violets are Violet
1 nanometer = 10 -9 meters
Ex: 600 nm = 6.00 x 10-7m
What is the speed of Light?
Speed of Light
• The speed of light can be defined as the speed it
takes light to travel one meter in 1/299,792,458
of a second.
• Presently, the speed of light has a fixed value of
299,792,458 m/s. or……..
• c = 3.00 × 108 m/s;
c=f λ
• Who measured the speed of light?
c=f λ or v=f λ
• A cell phone transmits at a frequency of
1.33 x 108 Hz. What is the wavelength of the
electromagnetic wave used by this phone?
• c=f λ
• 3.00 × 108 m/s = 1.33 x 108 Hz (λ)
• λ = 2.26 m
Galileo
One of the first attempts to measure the speed of
light. What do you think he discovered?
Conclusion: Light was really fast!!!!
Romer: Using the moons of Jupiter to
Determine the Speed of Light
c=f λ
• A television is tuned to a station broadcasting at
a frequency of 7.30 x 107 Hz. For best
reception, the rabbit-ear antenna used by the TV
should be adjusted to have a tip-to-tip length
equal to
one-third a wavelength of the broadcast signal.
Find the optimum length of the antenna.
• c=f λ
• 3.00 × 108 m/s = 7.30 x 107 Hz (λ)
• λ = 4.11 m
• So, 4.11/3 = 1.37 m
Speed of Light
Albert Michelson
Figure 25-7
Fizeau’s Experiment to Determine the Speed of Light
Doppler Radar
Microwaves
• A microwave oven produces electromagetic
waves with a wavelength of about 12 cm. What
are the frequency of such waves?
• c=f λ
• 3.00 × 108 m/s = (f) 0.12 m
• λ = 2.26 m
Doppler: Red Shift / Blue Shift
Which part of the Galaxy above will produce a
Red Shift and Which part will produce a Blue
Shift?
Top Blue, Middle Red, Bottom Red