WAVES
WAVES

AND
E NERGY
Waves and Energy

Wave – a traveling disturbance that carries
energy from one place to another

Waves do not carry matter; waves carry
energy

Vibration – movement that follows the same
path over and over again

Wave – movement of energy from a vibrating
source outward
Medium

The matter or substance through which a
wave is transmitted

Ex. Water – medium for ocean waves

Air – medium for sound
M ECHANICAL

waves that require a medium

Ex. Sound and water waves
WAVES
E LECTROMAGNETIC

Wave that consists of
electric and magnetic
fields

Do not require a
medium

Ex. Light,
microwaves, x-rays
WAVE
C HARACTERISTICS

Amplitude

Wavelength

Frequency
OF
WAVES
Amplitude

Greatest distance from normal resting
position to top (crest) of the wave

Indicates the amount of energy carried by
the wave
Wavelength

Distance between two crests or two troughs
(lowest point)

Usually measured in meters or centimeters

Symbol for wavelength is lambda λ
Frequency

Frequency – the number of complete waves
or complete cycles per unit time

Unit: Hertz (Hz) = 1 wave/second
T YPES

Transverse waves

Longitudinal Waves

OF WAVES
AKA compressional wave
T RANSVERSE


WAVES
A wave in which the motion of
the medium is at right angles to
the direction of the wave

Movement of particles is up
and down – vertical

Movement of the wave is
horizontal
Ex Waves on a rope, water
waves, light, electromagnetic
waves
L ONGITUDINAL WAVES

AKA compressional wave

Wave in which the motion of the medium is
parallel to the direction of the wave


A series of compressions and rarefactions

Rarefaction – space in the medium in which
there are fewer particles
Ex Sound waves
S PEED
OF
WAVES
 Speed = frequency x wavelength

Speed of a wave is constant
within the same given medium

If frequency is increased then
wavelength must decrease for
constant speed to be maintained
The speed of a wave depends upon
the medium

The density of the medium
affects the speed of
mechanical waves
o
The more dense a medium , the
slower light waves travel but
the faster sound waves travel.
Elasticity of the medium
affects the speed of waves

Elasticity – ability of a
medium to return quickly to
its original shape after being
disturbed

The more elastic – the faster
the wave
WAVE I NTERACTIONS

Reflection

Refraction

Diffraction

Interference

Standing waves

Resonance
R EFLECTION

Bouncing back of waves upon reaching
another surface

Echo

Mirror image
L AW

OF
R EFLECTION
The angle of incidence (i) is equal to the angle of
reflection (r)

Ray – line drawn in the direction of motion of a
wave

Incidental ray – incoming ray (incoming wave)

Reflected ray – ray (wave) that bounces off
barrier

Angle of incidence (i) – angle formed by the
incident ray and the normal

Angle of reflection (r)- angle formed by the
reflected ray and the normal

Normal – line drawn perpendicular to barrier
Refraction

The speed of a wave changes as the wave travels
from one medium to another

Refraction – the bending of waves due to a change in
speed

Refraction occurs because waves move at different
speeds in different mediums

If wave slows down it is bent to the normal

If it speeds up, it is bent away from the normal
D IFFRACTION

The bending of waves around the edge of an
obstacle or through a narrow opening
I NTERFERENCE

Interaction of waves that occur at the same place at
the same time; the wave combine to make a single
wave

Constructive interference – crest meets crest; the
amplitudes add together creating a larger amplitude

Destructive interference – crest meets trough; the
amplitudes subtract from one another creating a
smaller amplitude
E XAMPLE OF DESTRUCTIVE
I NTERFERENCE
S TANDING WAVES


Wave that does not appear to be moving; occurs at the
natural frequency of the material

Nodes – points at which destructive interference results in no
energy displacement

Antinodes – points at which constructive interference causes
maximum energy displacement
Resonance frequency – frequency at which a standing
wave occurs
R ESONANCE

The ability of an object to vibrate by
absorbing energy at its natural frequency

Video

Video 2
P OLARIZATION

Alignment of vibrations in a
transverse wave

Usually by filtering out waves
of other directions

Polarizing filters – transmit only
light waves that vibrate in the
same plane

Polarized sun glasses

Reduce glare