Sound & Light
Chapter 15
1
Sound

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
Sound waves are
caused by vibrations,
and carry energy
through a medium.
Sound waves are
longitudinal waves.
Speed of sound
depends on the
medium.
2
Speed of Sound



Speed of sound at room
temperature is about
346 m/s.
An increase in
temperature increases
the speed of sound.
Sound waves travel
faster in liquids &
solids than gases.
3
Loudness determined by Intensity



Intensity of a sound wave
describes the rate at which
a sound wave transmits
energy through a given
area of the medium.
Loudness depends on the
intensity of the sound
wave.
The greater the intensity,
the louder the sound.
4
Relative Intensity


The relative intensity
of sounds is found by
comparing the intensity
of a sound with the
intensity of the quietest
sound a person can
hear.
Relative intensity is
measured in units
called decibels.
5
Pitch


The pitch of a sound is
related to the frequency
of sound waves.
High pitch correspond
to a high frequency,
and low pitch
corresponds to a low
frequency.
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What type of wave is sound?
A.
B.
C.
D.
longitudinal
seismic
surface
transverse
28
0
A.
B.
0
C.
0
D.
7
Human Hearing


Infrasound is sound
that has a frequency
below human hearing.
Ultrasound is sound
that has a frequency
above human hearing.
8
Musical Instruments


Fundamental frequency is
the frequency of a standing
wave which wavelength is
twice the length of a string
on an instrument.
Instruments vibrate at their
fundamental frequency and
whole-number multiples of
that frequency called
harmonics.
9
Instruments Amplify Sound


Vibrations from
plucking strings of an
instrument are called
forced vibrations.
The body of a guitar
vibrate at certain
specific frequencies
called natural
frequencies.
10
Resonance


Resonance is when an
instrument vibrates at
its natural frequency.
The natural frequency
of an object depends on
its:



Shape
Size
mass
11
Hearing




Sound passing through the
outer ear to the middle ear.
The middle ear consists of
the hammer, anvil &
stirrup.
The middle ear vibrates the
fluids in the cochlea.
The cochlea has tiny hairs
that are stimulated and
transmit the impulses to the
brain.
12
Application of Sound


Sonar is a system that
determines distance by
measuring the time it takes
for sound waves to be
reflected back from a
surface.
Ultrasound is a device that
uses the echoes of high
frequency ultrasound to
produce images of internal
organs.
13
Assignment:





Design an musical instrument from materials you
have at home.
Classify it as a woodwind, brass, percussion or string
instrument.
Be able to explain the theory behind the instrument
playing different tones.
Be able to present music and play it on the
instrument in a recognizable way.
Due Monday.
14
Light as a Wave




Light travels as
transverse waves.
Light does not require
a medium.
Light waves are called
electromagnetic waves.
The wave model is
supported because light
can reflect, refract and
diffract.
15
Light as a Particle



In the particle model,
light travel in photons.
Photons are considered
particles.
Photons don’t have
mass, they are bundles
of energy.
16
Frequency of Light



The amount of energy is
proportional to the frequency of
the corresponding
electromagnetic wave.
A photon with twice as much
energy corresponds to a wave
with twice the frequency is in the
ultraviolet range.
A photon with half as much
energy corresponds to a wave
with half as much frequency is in
the infrared range.
17
Speed of Light



Light travels at the
speed of 300,000 km/s.
Light travels fastest in
a vacuum and slower in
any medium.
Nothing travels faster
than light in our
universe.
18
Intensity of Light



The brightness of light
depends on the intensity of
the light.
Intensity depends on the
amount of light that passes
through a certain area of
space.
Light spreads out from the
source. The farther from
the light source, the
dimmer the light.
19
Electromagnetic Spectrum




Electromagnetic spectrum
consist of light of all possible
energies, frequencies and
wavelengths.
Ultraviolet light has higher
energy and shorter wavelengths
than purple light.
X-rays has higher energy and
shorter wavelengths.
Gamma rays has the highest
energy and shortest wavelengths.
20
Electromagnetic Spectrum continued




Infrared waves has
wavelengths slightly
longer than red light.
Microwaves are used
for cooking.
Radio waves have the
longest wavelengths.
Radar is used to
determine location.
21
Reflection and Color



Reflection occurs as
light hits a barrier and
bounces off of the
barrier.
The incidence ray is
the incoming light
waves.
The reflected ray is the
light waves that bounce
off of the barrier.
22
Reflection (continued)



The angle of incidence is
defined by the angle
between the normal and the
incidence ray.
The angle of reflection is
defined by the angle
between the normal and the
reflected ray.
The law of reflection states
that the angle of incidence
is always equal to the angle
of reflection.
23
Types of Reflection


Smooth reflection
occurs when the light
waves hit a smooth
surface.
Diffuse reflection
occurs when the light
waves hit a rough
surface and the light
waves are scattered.
24
Types of Mirrors



Concave mirrors are
mirrors that curve inward.
These type of mirrors can
produce virtual & real
images.
Convex mirrors are mirrors
that bulge outward. These
type of mirrors can produce
virtual images.
Plane mirrors produce
virtual images.
25
Type of Images


Real images are
inverted images formed
where rays of light
meet.
Virtual images are
upright images formed
where rays of light
appear to meet or come
from.
26
Colors



The color we see is the
light being reflected
from the object.
Additive primary
colors are red, green &
blue.
Subtractive primary
colors are yellow, cyan
and magenta.
27
Colors and Pigments


If all colors are
reflected, you see white
light.
If all colors are
absorbed, you see
black.
28
Refraction


Refraction happens
when light waves
changes speed as it
goes through different
mediums.
As light waves change
speed the waves bend.
29
Effects of Refraction


Refraction makes
objects appear to be in
different positions.
Refractions in the
atmosphere creates
mirages.
30
Snell’s Law

Snell's Law Snell's law
(also known as Descartes'
law or the law of
refraction), is a formula
used to describe the
relationship between the
angles of incidence and
refraction, when referring
to light or other waves,
passing through a boundary
between two different
media, such as air and
glass.
31
Total Internal Reflection


If the angle at which light
rays meet the boundary
between two mediums
becomes small enough, the
rays will be reflected as if
the boundary were a
mirror.
This angle is called the
critical angle, and this type
of reflection is called total
internal reflection.
32
Lenses



A lens is a curved piece
of glass.
Lenses can magnify
images.
Magnification is any
change in the size of an
image compared with
the size of the object.
33
Type of Lenses


Converging lens bends
the light inward that
produces a virtual or
real image. (convex
lens)
Diverging lens bends
the light outward and
can produce only a
virtual image. (concave
lens)
34
Prisms



Prism is a triangular
shaped piece of glass
that refracts light.
Prism disperse light.
Dispersion is the
separation of light into
separate colors because
of the differences in
wave speed.
35