Waves
A wave is a disturbance in a medium that
carries energy without a net movement of
particles.
•
Transfers energy.
•
Usually involves a periodic, repetitive movement.
•
Does not result in a net movement of the medium or
particles in the medium (mechanical wave).
Some waves do not need matter (called a
“medium”) to be able to move (for example,
through space).
These are called electromagnetic waves (or
EM waves).
Some waves MUST have a medium in order
to move. These are called mechanical
waves.
waves
Transverse
Longitudinal
Transverse Waves
Waves in which the particles
in the medium moves at right
angles to the direction of the
wave.
• Longitudinal
Wave:
waves in which particles in the
medium moves in parallel to the
direction of movement of the
wave.
Examples of transverse waves:
Water waves (ripples of gravity waves, not
sound through water)
Light waves
S-wave earthquake waves
Stringed instruments
Torsion wave
The high point of a transverse wave is a crest.
The low part is a trough.
.
Examples of longitudinal waves:
Sound waves
P-type earthquake waves
Parts of longitudinal waves:
Compression: where the
particles are close together.
Rarefaction: where the particles
are spread apart.
Waves transfer energy and information from
one place to another, but they do not
transfer material.
Wave Properties
Amplitude is the maximum displacement (change in position) from
the undisturbed position.
Wavelength (λ) is the distance in metres from any point on the
wave to an exactly similar point.
Frequency is the number of waves that pass a
point in one second. This depends on how fast
the waves is vibrating.
The frequency is usually expressed in hertz (Hz)
cycle (wave) per second.
Example:
Four waves pass a point in one second. The
A wave takes two seconds to pass a point. The
The higher the frequency, the more energy in
the wave.
10 waves going past in 1 second = 10 Hz
1,000 waves go past in 1 second = 1,000 Hz
1 million waves going past = 1 million Hz
Wave speed depends on the medium that the wave is
travelling through:
distance wave travels = wave speed × time
(d = v × t )
Example: A water wave travels at 5 cm/s. In 4 s it travels d = 5 cm/s × 4 s = 20
The wave equation relates the wavelength and frequency to
For all waves: wave speed = frequency × wavelength
(v = f λ where f is in Hz, λ is in m, v is in m/s).
Example: Water waves with wavelength λ = 10 cm and frequency f = 4 Hz have a
cm/s.
Examples:
1. A sound wave has a frequency of 10,000
Hz and a wavelength 0f 0.033 m. What is the
speed of the wave?
Examples:
2. A radio wave of speed 300000 km/s has a
frequency of 600 MHz. What is its
wavelength?
Examples:
3. What is the frequency of an ultrasound
wave of speed 1500 m/s and wavelength
0.05 m?
Label the wave:
A
B
C
D
Describe the motion of the particles in the
medium for each type of wave. How does this
motion compare to the direction the wave
travels?
a.transverse wave
b. longitudinal wave.
c.What do waves transfer?
Nature of wave:
Reflection: When waves bounce off a surface.
If the surface is flat, the angle at which the wave
hits the surface will be the same as the angle at
which it leaves the surface
(angle in = angle out).
This is the law of reflection.
Refraction: Waves can bend.
This happens when a wave enters a new
medium and its SPEED CHANGES.
The amount of bending depends on the
medium it is entering.
Diffraction: The bending of waves AROUND an object.
The amount of bending depends on the size of the obstacle
and the size of the waves.