Sound, Light, Electromagnetic
Spectrum and Mirrors
Sound
 Sound waves are
compressional waves.
 Two regions: compressions
and rarefactions
 Sound travels faster in liquids
and solids than in gases.
 Why? The molecules in liquids
and solids are closer
together.
Sound
 Humans hear sound waves in a limited frequency
range.
 20 Hz-20,000 Hz
 Other ranges: dolphins 70 Hz-150,000Hz
 Dogs 40 Hz-46,000 Hz
 Infrasound-any sound lower than 20 Hz
 Ultrasound- any sound higher than 20,000Hz
 Ultrasound imaging is used in medicine
 Sonar- is a system that uses reflected sound waves to
determine distances & location of objects
 Bats use sonar to navigate in flight & locate food
Ultrasound imaging used in
medicine-echoes of very
high frequency ultrasound
waves between 1million-15
million Hz are used to
produce computerized
images called sonograms.
Bats use sonar to navigate in
flight & locate food

Loudness is determined by…





the amount of energy in the wave
As the energy ↑, the amplitude of the wave will ↑
Your distance from the source the sound waves
Intensity of a sound describes its loudness
Intensity is measured in decibels(dB)
The Doppler Effect
 The observed change pitch or wave frequency due to
a moving wave source.
 You hear the high pitch of the siren of the
approaching ambulance, and notice that its pitch
drops suddenly as the ambulance passes you. That is
called the Doppler effect.
 Pg 331 Figure 9
Doppler Effect
The sound is louder due
to wave compressions
The sound is lower due to
wave rarefactions.
Electromagnetic Waves
 Electromagnetic
waves are made by
vibrating electric
charges and can
travel through space
where matter is not
present.
 Electromagnetic
waves do not require
a medium.
The Electromagnetic Spectrum
 Gamma rays –short wavelengths and high frequency- very
powerful and dangerous
 Radio waves-long wavelengths & low frequency
The Nature of Light:
Wave-Particle duality
 Light can be modeled as a wave
 Light waves which are electromagnetic waves consists of
changing electric & magnetic fields
 Light waves may reflect when they meet a mirror, refract when
they pass through a lens, or diffract when they pass through a
narrow opening.
 Light can be modeled as a stream of particles
 Photons- are a particle of light/bundle of energy
The speed of light depends on the
medium!
 Speed of light (c) = 3 x 108 m/s (in a vacuum)
 Light is the fastest signal in the universe
 Nothing can travel faster than the speed of light.
 When light travels through different media, it slows
down.
The speed of light depends on
the medium!
Medium
Vacuum
Air
Ice
Water
Quartz
Glass
Diamond
Speed of light (x 108
m/s)
2.997925
2.997047
2.29
2.25
2.05
1.97
1.24
Mirrors
 Flat mirrors form virtual
images by reflection.
 When you look into a mirror,
you see an image of yourself
behind the mirror.
 Virtual image is an image
that forms at a point from
which light rays appear to
come but do not actually
come
 Real image is an image of an
object formed by many light
rays coming together in a
specific location.
Types of Mirrors
 Curved mirrors can distort
images
 Since the surface is not flat,
the line perpendicular to the
mirror (normal) points in
diff. directions for diff. parts
of the mirror.
 Mirrors that bulge out are
called convex mirrors
 Mirrors that are indented
are called concave mirrors
 Concave mirrors create real
images.