Chapter 14 - Waves
• A wave is a rhythmic disturbance that
carries energy through matter
• Waves need a material (medium) to
travel through.
• This is why sound doesn’t travel
through a vacuum
• Wave Pulse – a single disturbance
• Continuous Wave – continuous
disturbance
2 Types of Waves
• Transverse – a wave
that moves
perpendicular to the
direction of movement.
Ex: light
• Longitudinal – a wave
that moves parallel to
the direction of the
wave.
Ex: sound
Anatomy of a Wave
Wavelength (λ) – distance
between two similar points
Wave Height – from top to
bottom of a wave
Crest – top of the wave
Trough – bottom of the wave
Amplitude (A) – distance
from equilibrium
Waves at Boundaries
• The waves that strikes a
boundary is called an
incident waves.
• When a wave strikes a
boundary some energy is
transmitted and some is
reflected backward
(reflected wave).
• Whether the reflected
wave is upright (erect) or
downward (inverted)
depends on the density of
the two mediums
Interference
Superposition - when
two waves meet at
the same place at the
same time.
Destructive interference
– superposition with
opposite amplitudes
Constructive
interference –
superposition with
same amplitudes.
The result is a wave
with larger amplitude.
Up To Now
• Waves need a material (medium) to travel
• 2 Types of Waves – Transverse and Longitudinal
• Wavelength (λ) – distance between two similar points
• Amplitude (A) – distance from equilibrium
• Waves at boundaries
– Rigid – almost all the energy is reflected back and inverted
– Less Rigid – some energy is reflected back on the same side,
some is transmitted through
• The velocity only depends on the medium
• Interference
Some Details
• The speed of a wave (velocity) = change in
distance/change in time
• The velocity only depends on the medium (ex. Light
slows down in a prism)
• The greater the amplitude the more energy the wave
has. Depends on how the wave is made not its speed.
• Energy = amplitude2
• Period (T) = time it takes the wave to return to the same
point (pendulum)
• Frequency (f) = number of oscillations (periods) a wave
makes each second. Measured in Hertz (Hz)
• f=1/T (inverse relationship)
• Both the period and the frequency depend on the waves
source not the medium or the waves speed.
V=λf
Velocity = (Wavelength)(Frequency)
How are things related?
• If λ decreases, f increases, v is the same,
a is the same
• If λ increases, f deceases, v is the same, a
is the same
Standing Waves
A wave appears to stand still
when the period of the
rope’s vibration equals the
time needed for the wave to
make one round.
Node – the point that doesn’t move
when two pulses meet. Created by
destructive interference
Antinode- the largest amplitude.
Created by constructive interference.
The 2 pulses will pass through each
other without changing shape or size.
Law of Reflection
• the angle of incidence is
equal to the angle of
reflection
Refraction
• the change in direction of
waves at the boundary
between two different
medium.