Waves are present everywhere. Whether we recognize it or not, we encounter waves
on a daily basis. We experience a variety of waves on daily basis including sound
waves, radio waves, microwaves, water waves, visible light waves, sine waves, stadium
waves, earthquake waves, cosine waves and waves on a string. Besides these waves
we also experience various other motions which are similar to those of waves and
are better referred as wavelike. These phenomena include the motion of a pendulum,
the motion of a mass suspended by a spring and the motion of a child on a swing.
Wave phenomena emerge in unexpected contexts. The flow of traffic along a road can
support a variety of wave-like disturbances as anybody who has experienced a slowly
moving traffic will know. The beat of your heart is regulated by spiral waves of
chemical activity that swirl across its surface. You control the movement of your
body through the action of electrochemical waves in your nervous system. Finally,
quantum physics has revealed that, on a small enough scale, everything around us
can only be described in terms of waves. The universe isn’t really mechanical in
nature. It’s made of fields of force. When a radio antenna makes a disturbance in
the electric and magnetic fields, those disturbances travel outward like ripples
of water in a pond. In other words, waves are fundamental to the way the universe
Wave Motion Definition:
A waves motion can be defined as a disturbance that travels through a medium from
one place to another. We consider the case of a slinky wave. When the slinky is
stretched from end to end and is held at rest, it assumes an equilibrium position
which is the position of rest. In order to induce a wave in slinky we first displace
a particle of slinky from its position of rest. Wherever we move the coil whether
upward or downward, forward or backward, it returns to its original position. But
this movement creates a disturbance. If the slinky was moved in a back and forth
direction then the disturbance observed in the slinky is called a slinky pulse.
A pulse is a single disturbance that moves through a medium form one place to another.
However, if the first coil of the slinky is continuously and periodically vibrated
in a back-and-forth manner, it induces a repeating disturbance that continues for
a longer duration. This disturbance is termed as a wave.
Frequency and Period of Wave:
The frequency of a wave refers to how often the particles of the medium vibrate
when a wave passes through the medium. In mathematical terms, the frequency is the
number of complete vibrational cycles of a medium per a given amount of time. The
unit of frequency is the Hertz (abbreviated Hz) where 1 Hz is equivalent to 1 cycle/second.
If a coil of slinky makes 2 vibrational cycles in one second, then the frequency
is 2 Hz. If a coil of slinky makes 3 vibrational cycles in one second, then the
frequency is 3 Hz. The period of a wave is the time for a particle on a medium to
make one complete vibrational cycle. Period, being a time, is measured in units
of time such as seconds, hours, days or years. The period of orbit for the Earth
around the Sun is approximately 365 days; it takes 365 days for the Earth to complete
Types of Wave Motion:
Waves come in various shapes and forms. Though the basic characteristics of wave
motion are same and present in all waves but they can be distinguished on the basis
of some distinguishing features.
Transverse Wave Motion:
The wave in which particles of the medium move in a direction perpendicular to the
direction of the wave is called a transverse wave. Now again if we consider the
case of a slinky then if it is stretched in a horizontal direction and a movement
is produced in the first coil by moving it up and down, energy is transported from
left to right. Since the movement of particles is perpendicular to the direction
of movemnt of wave so it is an example of traneverse wave.
Longitudinal Wave Motion:
The wave in which the particles move in a direction parallel to the direction of
the movement of the wave is called a longitudinal wave. As discussed in the last
case, in a slinky, once a disturbance is produced, the energy is transported from
left to right. The particles of the medium move in a direction parallel to that
of the pulse. Hence, such waves are longitudinal waves.
Waves can also be categorized on the basis of their capability of transferring energy
through a vacuum.
Electromagnetic wave Motion:
Waves which are capable of transmitting energy through a vacuum and are produced
by the vibration of charged particles are called electromagnetic waves. Light waves
are an example of these waves. Electromagnetic waves are produced on Sun and travel
to Earth through vacuum. These waves are responsible for the existence of life on
Mechanical Wave Motion:
Those waves which cannot transmit their energy through a vacuum and require a medium
for same are called mechanical waves. Various examples include sound waves, water
waves, slinky waves etc.
Equation of Wave Motion:
The wave motion equation can be expressed as
Speed = Wavelength • Frequency
It states the mathematical relationship between the speed (v) of a wave and its
wavelength () and frequency (f). Using the symbols v, λ , and f, the equation can
be rewritten as v = f • λ
Wave Motion is an important topic in the Physics syllabus of the IIT JEE. The topic
usually fetches around 5-6 questions on an average.