light as a wave: part 1 snc2d. what is a wave? a wave is a disturbance which carries energy from one...
TRANSCRIPT
What is a wave?
A wave is a disturbance which carries energy from one location to another.
The material the disturbance travels through is the medium.
The movement of the disturbance is referred to as propagation.
2 Types of Waves
A longitudinal wave is a wave in which the particles of the medium move in a direction parallel to the direction of propagation.
2 Types of Waves
A longitudinal wave is a wave in which the particles of the medium move in a direction parallel to the direction of propagation.
2 Types of Waves
A transverse wave is a wave in which the particles of the medium move in a direction perpendicular to the direction of propagation.
Snapshot of a Wave
The positions of maximum displacement are referred to as crests (positive displacement) and troughs (negative).
The maximum displacement is the amplitude.
Snapshot of a Wave
The distance between one crest and the next crest (or one trough and the next trough) is the
Snapshot of a Wave
The distance between one crest and the next crest (or one trough and the next trough) is the wavelength, represented by
Snapshot of a Wave
The distance between one crest and the next crest (or one trough and the next trough) is the wavelength, represented by .
Snapshot of a Wave
The time it takes one complete wavelength to pass a single point is the period, represented by
Snapshot of a Wave
The time it takes one complete wavelength to pass a single point is the period, represented by T.
Snapshot of a Wave
The number of complete wavelengths that pass a single point in one second is the frequency, represented by f.
Tf
1
Frequency
Frequency is measured in units of s-1 or Hertz (Hz).
“I do not think that the wireless waves I have discovered will have any practical application.”
Wave Speed
The speed of a wave is therefore:
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
fTt
dv
Wave Speed
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
Wave Speed
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
?
:
256
344
:
Unknown
Hzf
v
Givens
sm
Wave Speed
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
?
:
256
344
:
Unknown
Hzf
v
Givens
sm
Wave Speed
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
?
:
256
344
:
Unknown
Hzf
v
Givens
sm
Wave Speed
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
?
:
256
344
:
Unknown
Hzf
v
Givens
sm
Wave Speed
Practice Question: What is the wavelength of a wave with a speed of 344 m/s and a frequency of 256 Hz?
?
:
256
344
:
Unknown
Hzf
v
Givens
sm
m
HzSolve
f
vfvSelect
sm
34.1
256
344:
:
Light is an “EM” wave
Light is actually a transverse wave, but the perpendicular-to-propagation disturbance is not of particles of a medium but of the electric and magnetic (EM) fields
The Speed of Light
Because light waves do not need a medium, they can travel through a vacuum (empty space) and do so at the speed of light: c =
The Speed of Light
Because light waves do not need a medium, they can travel through a vacuum (empty space) and do so at the speed of light: c = 3.0 x 108 m/s.
Light-years
A light-year is the distance light would travel in 1 year.
Practice Question: How far (in m) is 1.0 light-years?
Light-years
A light-year is the distance light would travel in 1 year.
Practice Question: How far (in m) is 1.0 light-years?
yr
m
yr
d
d
h
h
s
s
m
1
105.9
1
365
1
24
1
min60
min1
60
1
100.3 158
The Speed(s) of Light
Light will travel slower in denser media (e.g. glass), but the speed in air is still effectively 3.0 x 108 m/s and
c f
or
fcand
c
f