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Sound and Light.notebook
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January 08, 2018
Sound & Light
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January 08, 2018
Waves
A repeating disturbance or movement that transfers energy through matter or space
Ex: ocean waves, earthquakes, ripples in a pond
Waves transfer energy, not matter
Demo
What creates a wave?
Vibrations: movement up/down or side to sideExamples: vocal cord, tuning fork, pendulum, string instruments
Types of Waves: (2 types)
1. Mechanical Waves :
waves that travel through a medium (solid, liquid, gas)
2. Electromagnetic Waves
waves that do not require a medium to travel through
Mechanical & Electromagnetic waves can be either: > Transverse: matter in the medium moves back and forth at right
angles to the direction that the wave travels
> Compressional: matter in the medium moves back and forth along the same direction that the wave travels
Sound is a mechanical compressional wave.
Light is an electromagnetic transverse wave
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Anatomy of a Wave
Waves can differ in how much energy they transfer and in how fast they travel.
‐Crests (high points)
‐Troughs (low points)
‐Compressions (medium is close together)
‐Rarefactions (medium is farther apart)
Wavelength:
Distance between one point on a wave and the nearest point just like it
Unit: meters (m)
Frequency:
the number of wavelengths that pass a fixed point each second
unit: Hertz (Hz)
Frequency (F) = number of wavelengths/ time
Period:
the amount of time it takes one wavelength to pass a point
unit: seconds (s)
as frequency increases, period decreases
Amplitude
the maximum distance a wave causes the particles to move from the rest position
larger amplitude, more energy transferred
Unit: Meters (m)
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Wave Relationships
Wavelength and Frequency
as frequency increases, wavelength decreases.
Wave Velocity:
the speed of a wave depends on the medium it is traveling through.
sound travels faster in liquids and solids, while light travels slower in liquids and solids
Velocity of wave (m/s) = frequency (Hz) x Wavelength (m)
What is the velocity of a sound wave that has a wavelength of 2.0 m and a frequency of 170.5 Hz?
The lowestpitched sounds humans can hear have a frequency of 20.0 Hz. What is the wavelength of these sound waves if their velocity is 340.0 m/s ?
It takes a wave 14s to pass by a given point. What is the frequency of the wave? (Look back at the frequency equation).
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SoundCompressional wave
series of compressions and rarefactions
Interference:
When two or more waves overlap and combine to form a new wave
two types
1. Constructive Interference
two or more waves add together
when two compressions overlap
2. Destructive Interference
waves subtract from each other as they overlap
when a compression and a rarefaction overlap
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Intensity and Loudness
Intensity:
the amount of energy transferred by a sound wave through a certain area each second
as sound waves travel away from the source of the sound, the intensity of the waves spread out
measured in decibels (dB)
Loudness:
The human perception of sound intensity
Demo:
What happens to the loudness of the sound during constructive and destructive interference?
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Pitch & Frequency
Frequency (Hz)
the number of wavelengths that pass a point each second
Pitch
human perception of frequency
a healthy human ear can hear sound waves with frequencies form about 20 (Hz) to 20,000 (Hz)
Describe how pitch changes as frequency changes
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Resonance
the process by which an object is made to vibrate by absorbing energy at its natural frequency
all objects have their own natural frequencies of vibration (ex: striking a bell, or glass)
an object vibrates more strongly as it continues to absorb energy at its natural frequency (ex: glass vibrating to the point of shattering)
Demo
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Speed of Sound
the speed of a sound wave depends on the medium (solid, liquid, gas)
sound waves travel slowest in gases and fastest in solids
the speed of a sound wave depends on the temperature of the medium
sound waves travel faster in higher temperatures
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Properties of Light
Interaction of Light and Matter
Objects can absorb, reflect, and transmit light
The type of matter in an object determines the amount of light it absorbs, reflects, and transmits
Opaque, translucent, transparent
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Refraction
bending light
caused by a change in speed of a wave when it passes from one material to another
if light is traveling at an angle to the boundary between the materials and the speed of light is different in the two materials, the wave will be bent, or refracted
Index of Refraction
indicates how much the speed of light is reduced in the material compared to its speed in empty space
the greater the change in speed of the wave, the more the light will be bent
Demo
https://www.youtube.com/watch?v=fD1544bM_c4
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Law of Reflection
the angle at which a light wave strikes a surface is the same as the angle at which it is reflected
Regular vs. Diffuse Reflection
smooth surfaces reflect light waves in one direction (Regular)
textured surfaces reflect light waves in many directions (Diffuse)
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Mirrors any surface that produces a regular reflection (pool of water, shiny spoon, ect)
can be flat, curved inward, curved outward
Real vs. Virtual Images
your brain assumes that light travels in a straight line. As a result, rays that enter your eyes seem to come from behind the mirror...making the image seem to come from behind the mirror
This is a virtual image
if light rays from an object pass through the location of the image, the image is called a real image
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Types of Mirrors:
Plane Mirror
flat, smooth
image appears upright and is a virtual image
Concave mirror
curved inward
image formed depends on the focal length
between one and two focal lengths: real, inverted and larger
closer than one focal length: virtual, upright, and larger
Convex mirror
curved outward
light rays diverge, so a virtual image is always formed
image is upright and smaller
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ColorThe color of an object depends on the wavelengths of light it reflects
White light is a blend of all colors of visible light
Example: When white light hits a "red" apple, the red light is reflected and the other colors are absorbed
We perceive different colors of light due to differing wavelengths
(Red= longest, lowest energy & Blue/Violet =shortest, highest energy)
Red, Green, and Blue cone cells in our eyes are sensitive to these colors
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PrismsDemo
Why are different colors of light separated out through a prism?
The prism refracts the light twiceonce when it enters the prism and again when it leaves the prism
Speed of light in a material depends on the wavelength of the light
Light waves with longer wavelengths are slowed less than light waves with shorter wavelengths...so...
Red wavelengths are bent the least, violet is bent the most..this difference in bending cause the colors of light to be separated
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Filters
transparent material that transmits one or more colors of light but absorbs all others
Example: Look at a blue object and a red object through a red filter
We can create any color light from three primary colors: Red, Green, and Blue
Try it out! Using your filters & a flashlight, mix together:
Red & Green:
Green & Blue:
Blue & Red:
Not the same for pigments...
Primary colors are Yellow, Cyan, and Magenta
That's why your printer ink cartridges are not Red, Green, and Blue
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WEIRD things our eyes "see" because of light & color...
http://www.eyetricks.com/rotatingdots.htm
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