physics unit 5 waves – light & sound - fcps · pdf fileexamples: gamma radiation,...
TRANSCRIPT
Physics Unit 5 Waves –
Light & Sound
Chapter 11-15
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)
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
Compressional (Longitudinal)•
Matter moves in the same direction as (along with) the wave front
compression
rarefaction
λ
Example: sound
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)
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
Frequency Comparisons•
Transverse •
Longitudinal
High frequency-purple light
Low frequency-red light
High frequency-High pitch
low frequency-low pitch
Amplitude Comparisons•
Transverse
High amplitude-bright light
Low amplitude-dim light
•
Longitudinal
High amplitude-loud
low amplitude-quiet
Transverse vs. Longitudinal
Check upWhich has a
longer λ?-A
Which has higher frequency?
-BWhich has higher
amplitude?-both same
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.
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
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
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
Refraction
This pencil appears to be bent because light traveling from the pencil to your eye is bent at the surface of the water.
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.
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.’
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.)
Name that interference
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
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.
Electromagnetic Spectrum•
Transverse waves that go in order of increasing frequencies (decreasing wavelengths)
•
some wave frequencies overlap
8._______
7._______
6._______
5._______
4._______
3._______
2._______
1._______
9._______ frequency10._______ wavelength
11._______ frequency12._______ wavelength
13._______ _______ _______ _______ _______ _______
Electromagnetic Spectrum
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
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
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
Interference
•
Sometimes wave run into each other. When this occurs, the waves combine to form a new wave.
Constructive Interference
•
If the waves add together in phase, they build on one another. A larger amplitude wave results.
Destructive Interference
•
If the waves add together out of phase, they cancel one another out. A smaller amplitude wave results.
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.”
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