Mechanical waves require a material
medium to travel (air, water, ropes). These waves are divided into three
different types: transverse, Longitudinal, and
Electromagnetic waves do not require a
medium to travel (light, radio).
Matter waves are
produced by electrons and particles.
What is meant by transverse waves? transverse waves
cause the medium to move perpendicular to the
direction of the wave.
What is meant by Longitudinal waves ? Longitudinal waves
cause the medium to move parallel to the
direction of the wave.
What is meant by Surface waves? Surface waves are
both transverse waves and longitudinal waves mixed in one medium.
What is a pulse?
Pulse is a single vibration. By moving a rope once, a single vibration is
produced. Click on the image to produce a pulse.
What is a wave?
A wave is a series of pulses. By moving a rope regularly up and
down, a traveling or periodic
wave is produced.
What is meant by "wave period"? Any point on a transverse wave moves up and down in a repeating
The shortest time that a point takes to return to the initial position (one
vibration) is called period, T. In this
example, every vibration is marked with a short pause.
What is meant by "wave frequency"? The number of vibrations per second is called
frequency and is measured in hertz (Hz). Here's the equation for
frequency: f = 1 / T
What is meant by "wave amplitude"?
The amplitude of a wave is the distance
from a crest to where the wave is at equilibrium. The amplitude is used to
measure the energy transferred by the wave. The bigger the distance, the
greater the energy transferred.
What is meant by "wave length"? The wavelength
is the distance between two crests or two troughs.
What is meant by "wave phase"? Phase is used to describe the starting
points of two waves. If their crests start at the same time they are
called in phase if not they are called out of phase. If the difference
between the two crests is 180 degrees they are called completely out of
What is meant by "wave front"? Wave front is a line or a surface
perpendicular to the wave direction and on which all disturbances at every
point have the same phase.
What is meant by ray? A ray is a line which represents the
direction of travel of a wave and it is always at right angle to the wave
How the speed of a wave is related to its length
and frequency? By knowing the frequency of a wave and its wavelength, we can
find its velocity. Here is the equation for the velocity
of a wave:
Does the velocity of a wave depend on frequency
or wave length of the wave? No it does not. The velocity of a wave is only affected by the
properties of the medium. It is not possible to increase the speed of a wave
by increasing its wavelength. By doing this, the number of vibrations per
second decreases and therefore the velocity remains the same.
A radio wave has a frequency of 93.9 MHz (93.9 *
106 Hz). What is its period? f = 93.9 * 106
f = 1 / T
T = 1 / f
T = 1 / 93.9 x 106 Hz
T = 1.06 x 10-8 s
If the velocity of a radio wave is 300 000 000
m/s (light speed) and its wavelength is 3.0 m, what is the frequency of the
000 000/3.0=100,000,000 Hz
What happens to a wave when it moves form one
medium to another medium?
Once a wave (incident wave) has reached the end of a medium, part of the
energy is transferred to the medium that is immediately next to it
(transmitted wave) and part is reflected backward (reflected wave).
The energy transferred depends on the difference between the
mediums. If there is a significant difference, almost all the energy will be
reflected. If the mediums are similar, most of the energy will be
transferred. However, the reflected waves will be inverted if the medium
that comes next is more dense or it won't be inverted if the medium is less
What is meant by Collision of waves? When two waves traveling in opposite
directions through the same medium collide, the amplitude of the resulting
wave will be the sum of the two initial waves. This is called interference
and there are of two types:
What is meant by a constructive interference? Constructive interference is
when the amplitudes of the initial waves are in the same direction. The
resulting wave will be larger than the original waves. The highest
point of a constructive interference is called an antinode.
What is meant by Destructive
Destructive interference is when the
amplitudes of the initial waves are opposite. The amplitude of the resulting
wave will be zero. The point in the middle of a destructive interference is
called a node and it never moves.
What is meant by reflection of waves? When a wave hits a barrier, it will be reflected
depending on the direction of the barrier
(normal). The angle between the incident wave and the normal is the same as
the angle between the normal and the reflected wave.
What is meant by refraction? When a wave enters a different medium (more
shallow region) at an angle, the direction of waves changes. This change is
What is meant by diffraction? When a wave travels through a small hole in
a barrier, it bends around the edges. This is called diffraction.
What happen to the following wave properties if
it undergoes reflection, refraction and diffraction?
Test yourself 1. The velocity of a wave is 420 m/s. If the frequency
of the wave is 85 Hz, what is its wavelength?
2. If a wave with a wavelength of 5.0 m has a 3.0 * 10-3
a. what is its frequency?
b. what is its velocity?
3. What is the period of a sound wave that has a frequency of
(e.g. "2.4 * 10E-3")
4. If a wave with a frequency of 342 Hz and a velocity of 234
m/s is produced...
a. what is its wavelength?
b. how far is the wave after 3.6 s?
5. A traveling wave is produced on a rope. The wave travels
until it hits a wall and it is reflected. If the speed of the wave is 1.8 m/s
and it takes 10.4 s to reach the origin again, ...
a. how long is this rope?
b. what is the wavelength of the wave if it has a period of