Waves
With Discussions on Sound and Light
What are waves? Key Point
• A wave is a disturbance in a medium that
transfers energy. There are two kinds of
waves, transverse and longitudinal. In a
transverse wave the particles move in a
direction perpendicular to wave motion. In
a Longitudinal wave the particles move in a
parallel direction to wave motion. All waves
have three features, wavelength (distance
between same point on neighboring waves),
amplitude (height of a wave), and
frequency (number of waves passing in a
certain time). Waves can be reflected
(bounced off an object) or refracted (bent
when changing mediums).
Two Kind of Waves
• Transverse • Longitudinal
• Particles in the • Particles in the
medium move up medium move back
and down and forth parallel to
perpendicular to the the direction of
direction of wave wave motion.
motion. • Two basic parts
• Two basic parts • Compression – part of
• Crest – high point of a the medium where
wave. particles are close
• Trough – low point of together.
a wave. • Rarefaction – part of
a medium where
particles are far
apart.
Two Kinds of Waves - Pictures
Wave Features
• Amplitude
• When a wave moves through a medium, the particles of the
medium are moved from their rest position. The distance
these particles are moved is called the amplitude of the
wave.
• Wavelength
• All waves have a certain length. The distance from the crest
of one wave to the crest of the next wave is the wavelength.
Wavelength can be measured using the same point on any
two waves. Wavelength is a measure of distance.
• Frequency
• A certain number of waves pass a point in a given amount of
time. The number of complete waves per unit of time is called
the frequency. Frequency is measured in waves per second.
The unit of frequency is the Hertz (Hz) = 1 wave / sec.
• Speed
• Wave speed = frequency x wavelength
Reflection
• Definitions
• Incident Wave – Wave that strikes a
barrier
• Normal – Line at right angles to a barrier.
• Reflected Wave – Wave that bounces
back from a barrier.
• Reflection – Bouncing back of a wave
after striking a barrier.
• Thoughts
• Think of watching waves at a beach, or an
echo.
Reflection Key Point
• Law of Reflection
• States that the angle of incidence is equal to
the angle of reflection.
• In other words…
• All waves carry energy, when a wave strikes
a barrier some energy is absorbed while the
remaining energy is bounced back, or
reflected. The angle at which a wave strikes
the barrier, the angle of incidence is the
same as the angle at which the reflected
wave leaves the barrier. These angles are
measured from the normal, a line
perpendicular to the barrier.
• Notice the green
wave with angle I.
• The red reflected
wave has angle R.
• The normal is the
grey dashed line.
Refraction Key Point
• Waves travel in straight lines through a medium,
when a wave enters a new medium at an angle
the wave is bent or refracted. There are three
ways a wave will refract:
• When a wave moves at an angle from a less dense
medium to a more dense medium, it is bent towards
the normal.
• When a wave moves at an angle from a more dense
medium to a less dense medium, it is bent away
from the normal.
• When a wave moves from one medium to another
medium along the normal, it is not bent.