Topic 5: Waves and the Particle
nature of light
Created @3 December 2025 07:35
Tags Notes
Basic Waves
Wave motion is a means of moving energy from place to place. For example: the
electromagnetic waves from the sun carry the energy to the Earth for the survival of living
things. The energy from sound reaches our eardrums to vibrate. Waves that move energy
from place to place without the transfer of matter are called progressive waves. Vibrating
objects act as a source of waves. For example, a vibrating tuning fork sets the air close to
it into oscillation, and a sound wave spreads out from the fork. In this article, two main
groups of waves are explained.
A. Transverse Waves
A transverse wave is one in which vibrations of the particles in the wave are at right
angles to the direction in which the energy of the wave is travelling.
Figure 1 shows a transverse wave moving along a rope. The particles of the rope
vibrate up and down, while the energy travels at right angles to this, from A to B.
There is no transfer of matter from A to B. Examples of transverse waves include
surface water waves and secondary seismic waves (S-waves).
Topic 5: Waves and the Particle nature of light 1
, Figure 1: A Transverse Wave
B. Longitudinal Waves
A longitudinal wave is one in which the direction of the vibrations of the particles in
the wave is along the direction in which the energy of the wave is travelling. Figure
2 shows a longitudinal wave moving along a stretched spring. The coils of the spring
vibrate along the length of the spring, while energy travels along the same line, from A
to B. Note that the spring itself does not move from A to B.
Examples of longitudinal waves include sound waves and primary seismic waves (P-
waves). In transverse waves, the ‘particles’ of the wave oscillate in a line at right
angles to the direction of travel. Light waves are an example of longitudinal waves.
Figure 2: Longitudinal Wave
C. Polarisation
Polarisation is the production of waves oscillating in one plane with respect to the line
of oscillation from a source of randomly oscillating waves. The different types of
oscillation of waves are illustrated in Figure 3.
Topic 5: Waves and the Particle nature of light 2
, Figure 3: Oscillation of Waves
Polarisation is done by passing the wave through a grid so that only the waves that can
fit through the slits continue through. Polarising of a light wave is illustrated in the
following figure.
Figure 4: Polarisation of Light Waves
Let us understand the process of polarisation of a light wave. Polaroid is a material
made of plastic. Long molecules of quinine iodo sulphate are lined up so that the light
wave oscillating in one particular direction can pass through. When an unpolarized
beam of light is directed at the polaroid, as shown in Figure 4, a beam of vertically
polarized light waves is transmitted. Two pieces of polaroid that have molecules
aligned at 90° to each other will not allow any light through.
D. Summary
Waves, which move energy from place to place without the transfer of matter, are
called progressive waves.
Two main groups of waves are longitudinal waves and transverse waves.
A transverse wave is one in which vibrations of the particles in the wave are at
right angles to the direction in which the energy of the wave is travelling.
Topic 5: Waves and the Particle nature of light 3
, A longitudinal wave is one in which the direction of the vibrations of the
particles in the wave is along the direction in which the energy of the wave is
travelling.
Polarisation is the production of waves oscillating in one plane with respect to
the line of oscillation from a source of randomly oscillating waves.
Progressive Waves
A. Displacement
The displacement of a particle on a wave is its distance in a specified direction
from its position.
A transverse wave is represented by plotting displacement on the y-axis and
distance (x) along the wave in the direction of energy travel, on the x-axis. Even
though, for a longitudinal wave, the displacement of the particles is along the
direction of the energy travel, the displacement is plotted on the y-axis and
distance along the x-axis. The graph for representing both transverse and
longitudinal waves is the same in shape as represented by the figure below. Wave
properties of waves can be determined by these graphs.
Figure 1: Wave Properties
B. Amplitude
The amplitude of the wave motion is defined as the maximum displacement of a
particle in the wave. Amplitude of a wave is shown in Figure 1.
C. Wavelength
Topic 5: Waves and the Particle nature of light 4
nature of light
Created @3 December 2025 07:35
Tags Notes
Basic Waves
Wave motion is a means of moving energy from place to place. For example: the
electromagnetic waves from the sun carry the energy to the Earth for the survival of living
things. The energy from sound reaches our eardrums to vibrate. Waves that move energy
from place to place without the transfer of matter are called progressive waves. Vibrating
objects act as a source of waves. For example, a vibrating tuning fork sets the air close to
it into oscillation, and a sound wave spreads out from the fork. In this article, two main
groups of waves are explained.
A. Transverse Waves
A transverse wave is one in which vibrations of the particles in the wave are at right
angles to the direction in which the energy of the wave is travelling.
Figure 1 shows a transverse wave moving along a rope. The particles of the rope
vibrate up and down, while the energy travels at right angles to this, from A to B.
There is no transfer of matter from A to B. Examples of transverse waves include
surface water waves and secondary seismic waves (S-waves).
Topic 5: Waves and the Particle nature of light 1
, Figure 1: A Transverse Wave
B. Longitudinal Waves
A longitudinal wave is one in which the direction of the vibrations of the particles in
the wave is along the direction in which the energy of the wave is travelling. Figure
2 shows a longitudinal wave moving along a stretched spring. The coils of the spring
vibrate along the length of the spring, while energy travels along the same line, from A
to B. Note that the spring itself does not move from A to B.
Examples of longitudinal waves include sound waves and primary seismic waves (P-
waves). In transverse waves, the ‘particles’ of the wave oscillate in a line at right
angles to the direction of travel. Light waves are an example of longitudinal waves.
Figure 2: Longitudinal Wave
C. Polarisation
Polarisation is the production of waves oscillating in one plane with respect to the line
of oscillation from a source of randomly oscillating waves. The different types of
oscillation of waves are illustrated in Figure 3.
Topic 5: Waves and the Particle nature of light 2
, Figure 3: Oscillation of Waves
Polarisation is done by passing the wave through a grid so that only the waves that can
fit through the slits continue through. Polarising of a light wave is illustrated in the
following figure.
Figure 4: Polarisation of Light Waves
Let us understand the process of polarisation of a light wave. Polaroid is a material
made of plastic. Long molecules of quinine iodo sulphate are lined up so that the light
wave oscillating in one particular direction can pass through. When an unpolarized
beam of light is directed at the polaroid, as shown in Figure 4, a beam of vertically
polarized light waves is transmitted. Two pieces of polaroid that have molecules
aligned at 90° to each other will not allow any light through.
D. Summary
Waves, which move energy from place to place without the transfer of matter, are
called progressive waves.
Two main groups of waves are longitudinal waves and transverse waves.
A transverse wave is one in which vibrations of the particles in the wave are at
right angles to the direction in which the energy of the wave is travelling.
Topic 5: Waves and the Particle nature of light 3
, A longitudinal wave is one in which the direction of the vibrations of the
particles in the wave is along the direction in which the energy of the wave is
travelling.
Polarisation is the production of waves oscillating in one plane with respect to
the line of oscillation from a source of randomly oscillating waves.
Progressive Waves
A. Displacement
The displacement of a particle on a wave is its distance in a specified direction
from its position.
A transverse wave is represented by plotting displacement on the y-axis and
distance (x) along the wave in the direction of energy travel, on the x-axis. Even
though, for a longitudinal wave, the displacement of the particles is along the
direction of the energy travel, the displacement is plotted on the y-axis and
distance along the x-axis. The graph for representing both transverse and
longitudinal waves is the same in shape as represented by the figure below. Wave
properties of waves can be determined by these graphs.
Figure 1: Wave Properties
B. Amplitude
The amplitude of the wave motion is defined as the maximum displacement of a
particle in the wave. Amplitude of a wave is shown in Figure 1.
C. Wavelength
Topic 5: Waves and the Particle nature of light 4
