Waves Notes

Need a medium
: air, water, slinky, etc.
Waves
Mechanical Waves
No medium required
Electromagnetic
Waves
Light, radio, x­rays
Sound, Earthquakes, etc
Transverse:
Longitudinal:
Surface:
vE&M = speed of light c = 3.00x108 m/s
ALL WAVES
A
­A
E.M. waves
v = 3.0x108 m/s
Sound waves
v = 343 m/s (air)
λ
v
v = λf
1
v = 300,000,000 m/s
v = 343 m/s
What is the wavelength of Z­100? f = 100.3 MHz
λ = 2.99 m
What is the frequency of a car horn whose wavelength is 15 cm?
f = 2287 Hz
2
Flash (light)
Bang (sound)
1609 m (1 mile)
tflash
tbang
The frequency of the sound of thunder is 75 Hz. What is the wavelength?
Earthquake!
v = 7000 m/s
v = 3000 m/s
3
Wave Reflection and Transmition
Fixed End (wall)
Free End Interference
Constructive
Destructive
2
3
1
­1
2
4
­1
1
3
1
­1
2
4
What will happen?
5
Waves in strings
• More Tension = Faster Wave
• Denser String = Slower Wave
vstring = A
0.02 kg
Tension
FT
DL
Linear
=
Density
B
1 m
mstring
Lstring 0.35 kg
C
1.5 m
Tension in both ropes is 100 N.
How long will a pulse take to get from A to B?
How long will a pulse take to get from B to C?
Sketch the wave(s) after point B..
6
Standing Waves
I am only 1
2
of a wave...Blast!
Strings
L
L
L
What harmonic?
What must the frequency be?
2.0 m
DL = 0.0032 kg/m
6 kg
7
0.4 m
f = 55 Hz
What harmonic?
λ = ?
v = ?
If the tension is 70 N what is the mass of the string?
8
Tubes
v = 343 m/s
Both Ends Open
Don't forget me!
L
1st
2nd
3rd
The frequency of the sound in the pipe is 232 Hz. What is the fundamental frequency?
What is the length of the pipe?
9
15 cm
What harmonic?
What must be the frequency?
How far apart are the nodes?
10
One End Closed
Don't forget me!
1st
3rd
5th
What is the frequency of the sound in the pipe?
2.5 m
What is the pipe's fundamental frequency?
11
0.2 m
What harmonic?
What is the λ? The L?
What will be the fundamental frequency?
12
13