Transcript Electromagnetic Waves

Electromagnetic Waves
AP Physics
Chapter 22
Vibration and Waves
22.1 Maxwell’s Equations
22.1 Maxwell’s Equations
After the work of Oerseted, Ampere and
Faraday
James Clark Maxwell – all
electric and magnetic
phenomena can be
described by four equations
Fundamental – even taking into account
relativity
Require Calculus
22.1
22.1 Maxwell’s Equations
1. Gauss’s Law – relates electric field to
electric charge
2. Magnetic field Law –
3. Faraday’s Law – electric field is produced
by magnetic field
4. Ampere’s Law – magnetic field produced
by an electric current, or changing electric
field
22.1
Vibration and Waves
22.2 Production of Electromagnetic Waves
22.2 Production of Electromagnetic Waves
How Electromagnetic Waves are Produced
EMR Production
The charged particle oscillate
As it travels one direction a current is
produced
This generates a magnetic field
When the direction changes, so does the
current and the magnetic field
22.2
22.2 Production of Electromagnetic Waves
Electric and magnetic fields are
perpendicular to each other
The fields alternate in
direction
These are
electromagnetic waves
Transverse
In general – accelerating electric charges
give rise to electromagnetic waves
22.2
Vibration and Waves
22.3 Electromagnetic Spectrum
S-93
A hamster is out driving his fancy hamster
wheel and yelling at a frequency of 1200 Hz.
He approaches an observer at 65 m/s. If the
observer runs away at 27 m/s, what is the
apparent frequency that the
observer hears? Assume that
the air temperature is 27.5oC.
22.3 Electromagnetic Spectrum
Electromagnetic Spectrum
22.3
22.3 Electromagnetic Spectrum
All EMR has a velocity of
in a Vacuum
Velocity decreases with increase in
optical density
The wave equation becomes
300, 000, 000
m
s
8 m
s
3x10
c f
Unlike Sound – energy depends on frequency
E  hf h  6.626 x10
34
J s
22.3
S-94
A mouse name Henry (French) plays a French
Horn. If the air temperature is 22oC
A. How long would the horn have to be to play
512 Hz as its fundamental frequency.
Assume that it acts like a closed tube.
B. What would be the velocity
and wavelength of that
frequency in the air?
C. What are the next two
harmonics that the French
horn would produce?
S-95
Next time you feel overweight, think of this cat.
He has big bones.
Good Luck on Your Test