physics unit 5 waves – light & sound - fcps · pdf fileexamples: gamma radiation,...
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Physics Unit 5 Waves –
Light & Sound
Chapter 11-15
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Wave•
A rhythmic disturbance that transfers energy through matter and/or a vacuum
•
Material a wave travels through is called the medium
•
2 types of waves:1. Transverse2. Compressional (Longitudinal)
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Transverse•
Matter in the wave moves at right angles to the direction of the wave front
mid line (resting position)
Crest
Trough
amplitude
Wavelength
(λ)
Examples: gamma radiation, x-ray, UV, visible light, infrared, microwave, radio, TV, water
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Compressional (Longitudinal)•
Matter moves in the same direction as (along with) the wave front
compression
rarefaction
λ
Example: sound
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Transverse & Compressional•
Amplitude (A)
-determined by amount of energy•
Wavelength (λ)
-determined by the wave frequency•
Frequency (f)
-number of waves per second-measured in hertz (Hz)
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Transverse & Compressional•
Velocity (v)
-v = λf-varies based on temperature, what it is traveling thru-stays the same in a given medium
•
velocity of light (all transverse waves)-
300,000,000 m/s
•
velocity of sound (longitudinal waves)-330 m/s
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Frequency Comparisons•
Transverse •
Longitudinal
High frequency-purple light
Low frequency-red light
High frequency-High pitch
low frequency-low pitch
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Amplitude Comparisons•
Transverse
High amplitude-bright light
Low amplitude-dim light
•
Longitudinal
High amplitude-loud
low amplitude-quiet
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Transverse vs. Longitudinal
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Check upWhich has a
longer λ?-A
Which has higher frequency?
-BWhich has higher
amplitude?-both same
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Waves -
Inteference•
Since waves travel at fast speeds in straight lines, eventually they will run into something.
•
Sometimes they run into things.•
Sometimes they run into other waves.
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Types of Interference1.
Reflection: a wave strikes an object and bounces off
2.
Refraction: a wave strikes an object and passes through it. The speed and direction of the wave are changed
3.
Absorption: a wave strikes and object and the wave energy is converted into heat and the temperature of the object increases
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Law of Reflection•
The angle of incidence is always equal to the angle of reflection.
•
The law holds true even if the reflected surface is not flat. The images do become distorted with a convex or concave surface
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2. Refraction•
Refraction: A wave passes through an object or medium and its speed and direction change. (The wave bends)•
When a wave is slowed, it bends towards the normal line
•
When a wave speeds up, it bends away from the normal line•
Index of Refraction: The amount that a medium (air, water, glass) bends a wave
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Refraction
This pencil appears to be bent because light traveling from the pencil to your eye is bent at the surface of the water.
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Refraction
It is difficult to dive for coins in a pool or spear fish in a lake because the light traveling from the object to your eye is bent at the surface of the water, changing its apparent location.
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RefractionDiamond has a high index of refraction. Light is bend sharply as it passes through diamond. This is why we can often see many different colors coming off of a diamond. Some light is also reflected off the surface of the diamond. This is sometimes called ‘sparkle.’
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Refraction•PPerhaps
the most common example of
refraction is…Sunlight refracts through droplets of water in the atmosphere, separating white light into a rainbow of color. (Just like a prism.)
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Name that interference
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Interference Examples (Even other waves!!!)
•
Reflection: Fun house mirror, duck in water, echo
•
Refraction: fish in tank, pencil in water, Rainbow
•
Absorption: Dark colors get hotter than light colors
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3. Absorption•
If a wave strikes an object and does not reflect off the surface or pass through, it is absorbed.
•
Wave energy is converted into heat and the temperature of the object increases.
•
Dark colors absorb more energy than light colors.
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Electromagnetic Spectrum•
Transverse waves that go in order of increasing frequencies (decreasing wavelengths)
•
some wave frequencies overlap
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8._______
7._______
6._______
5._______
4._______
3._______
2._______
1._______
9._______ frequency10._______ wavelength
11._______ frequency12._______ wavelength
13._______ _______ _______ _______ _______ _______
Electromagnetic Spectrum
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8.Gamma
7.x-ray
6.ultraviolet
5.visible light
4.infrared
3.microwaves
2.Radio
1.TV
9.Low
frequency10.Long
wavelength
11.High frequency12.Short
wavelength
13.red
orange
yellow
green
blue
Indigo
violet
Electromagnetic Spectrum
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Refracted/Reflected light
•
Colors of light in order-Red 700 nm-Orange 630 nm-Yellow 580 nm-Green 530 nm-Blue 480 nm-Indigo 430 nm-Violet 380nm
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Exploring Electromagnetic Spectrum
-The nitrogen and salt water in the ocean reflect and refract the
color blue the most, hence our skies are blue.
-
The clouds are white because they reflect all the colors of the
rainbow which make white light
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Interference
•
Sometimes wave run into each other. When this occurs, the waves combine to form a new wave.
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Constructive Interference
•
If the waves add together in phase, they build on one another. A larger amplitude wave results.
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Destructive Interference
•
If the waves add together out of phase, they cancel one another out. A smaller amplitude wave results.
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Interference Beats
•
Sometimes waves combine that work their way into and out of phase. This causes alternating patterns of constructive and destructive interference called “beats.”
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Doppler Effect•
The apparent shift in frequency caused by the movement of the sound source or the movement of the observer.
•
When the waves get crunched together (in front of the moving sound) the frequency of the wave is increased and the sound is high in pitch.
•
When the waves get spread apart (behind the moving sound) the frequency of the wave is decreased and the sound is low in pitch.
Low pitch
Fly by…
High pitch