Transcript WAVES - Mr. Hounslow's Physics Page

WAVES
THE ELECTROMAGNETIC
SPECTRUM
Waves are the result of a vibration
traveling from one location to another.
Waves are a method that enrgy uses to
travel from one location to another
velocity
Wave
Types of Waves
• Longitudinal or compression – vibrate
parallel to velocity. ex. Sound
• Transverse – vibrations perpendicular
to velocity. ex. Light and water waves
Crest
(Waves per Second)
Vertical displacement
λ
Frequency (f) in Hertz
Wavelength (λ) in meters
Amplitude
1 Hertz
1
second
Trough
2 Hertz
f
3 Hertz
Period and Frequency of Vibrations
• period – time (seconds) it takes
for 1 vibration (wave) to occur.
Unit: s
• frequency – number of
vibrations (waves) in a second
Unit: Hz or s-1
• f = 1/p AND p = 1/f
10Hz has a period of 1/10th of a
second
Period = 1/10 or 0.1
1 second
.1s .2s .3s .4s .5s .6s .7s .8s .9s 1s
f = 10 Hz
B I V
Gamma rays
G
10-10
Y
10-12
10-8
10-6
Ultraviolet
O
10-14
10-4
1020
1018
10-2
100
Infrared
102
Radio
TV, FM
1016
1014
1012
1010
108
AM
106
Frequency (f) in Hertz
High Energy
104
Microwave
X rays
1022
R
Wavelength (λ) in
meters
Low Energy
104
Electromagnetic Spectrum
Wave Uses
Relative Wavelength
What type of wave is it?
Use EM spectrum
1. λ = 2.90E-8 m
2. f = 6.35E6 Hz
3. λ = 7.01E-6 m
4. λ = 9.40E-14 m
5. f = 1.52E22 Hz
6. f = 3.99E8 Hz
7. λ = 8.34E-10 m
8. f = 2.76E10 Hz
Calculating frequency, wavelength, period and velocity
Symbol
Wavelength
λ
(Lambda)
Unit
Equation
Meters (m)
λ = v/f
Frequency
f
Hertz (Hz, s-1)
f = v/λ
f = 1/p
Period
p
s
1/f
velocity of light
v*
Meters per second (m/s)
v=fλ
c
Meters per second (m/s)
*Speed of light
(3.00E8)
v = velocity
c=fλ
Speed of Light
Speed of light (c) in a vacuum =
E8
3.00 meters per second (m/s)
In any other medium you have to
calculate velocity
v=fλ
Vacuum
Water
What is the wavelength?
What is the frequency?
What is the speed of the wave?
1) The wavelength of an x-ray is 4.32E-11 m. What is
its frequency?
3.00E8 m/s
E18 Hz
f = c/λ =
=
6.94
4.32E-11 m
2) Ultraviolet radiation from the sun has a frequency
of 2.49E16 Hz. What is its wavelength?
3.00E8 m/s
E-8 m
=
1.20
λ = c/f =
2.49E16 s-1
3) An infrared ray has a frequency of 1.01E10 Hz and a
wavelength of 2.95E-2 m. What is the speed of the
wave? 1.01E10 Hz x 2.95E-2 m =
2.98
E8
m/s
Radio Stations
Radio stations transmit their signal in megahertz (MHz)
1 megahertz = ? Hertz
106
98.5 MHz
1
x
106 Hz
E7
9.85
=
Hz
1 MHz
Radio Station’s Wavelength
What is the wavelength of these popular radio
stations?
1)
97.9 MHz (you have to convert to Hz first)
9.79E7 Hz
λ = c/f
3.06 m
2)
104.5 MHz
1.045E8 Hz
λ = c/f
2.87 m
3)
105.3
1.053E8 MHz
Hz
λ = c/f
2.85 m
How fast is the speed of light?
Going around the world 7.5 times a second
Interference
• Interference occurs when 2 waves
occupy the same space at the same
time.
• It can be “destructive” or
“constructive”, depending if the waves
are “in phase” or “out of phase”.
Interference
• Destructive
+
=
• Constructive
+
=
v=fλ
In a vacuum v = (c) speed of light
In any other medium you have to
calculate velocity
Faster =  f or ↓ λ
Slower = ↓f or  λ
Color Wavelengths
Color
λ
(m)
R
O
Y
G
B
I
V
7.00E-7 6.50E-7 6.00E-7 5.50E-7 4.70E-7 4.30E-7 4.00E-7
Baaaaaaa
!
Lambda!
B
A
C
D
2 Hertz
λ
f
3 Hertz
1 sec
1 sec
1 sec
1 sec
Period (time 1 swing)
Title
Period (time 1 swing) s
3
Title
No breaks!
0
String length (m)