Waves Unit
Waves
Waves Carry Energy
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A model for waves
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Think about the ripples made when you jump into water.
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The water molecules that make up the water pass the energy
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The water molecules transport the energy in a water wave by colliding with the
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Mechanical Waves
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The matter through which a mechanical wave travels is called a medium.
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Examples
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Students passing the object
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A mechanical wave travels as energy is transferred from one particle to another in the medium.
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Examples:
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Without the medium for energy to travel through you would not hear sound.
Transverse Waves
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As the energy moves through a transverse wave the matter does not move.
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The waves have peaks and valleys at regular intervals.
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High points of the wave = __________________________
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Low points of the wave = ___________________________
Compressional Waves
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In a compressional wave, matter in the medium moves forward and backwards in the same
direction that the wave travels.
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Compressional waves carry only energy forward along the spring.
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The area in which the wave is stretched apart is called rarefaction
Sound Waves
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Sound waves are compressional waves
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Examples of sound waves:
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Talking
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Music coming out of the speaker
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What do these examples have in common?
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Making Sound Waves
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How do vibrating objects make sounds waves?
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Drum Example:
1. When you hit the drum it starts vibrating up and down.
2. _________________________________________________________________
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3. When the drumhead moves downward, the molecules have more room to
spread farther apart – rarefaction
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Wave Properties
Amplitude
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The amplitude is ½ the distance between the crest and the trough
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In ____________________________, the amplitude is greater when the particles of the
medium are squeezed closer together in the compression.
Amplitude and energy
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Example:
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Electromagnetic waves that make up bright light have greater amplitudes than
the waves that make up dim light.
Sound waves
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Soft sounds= lower amplitude = less energy
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Greater amplitude = more energy
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Lower amplitudes = ____________________________
Wavelength
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For a compressional wave= wavelength is the distance between the centers of one
compression to the center of the next compression, or the center of one rarefaction to
the center of the next rarefaction.
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Electromagnetic waves that range from kilometers to no less the diameter of an atom.
Frequency
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Frequency of a wave is the number of wavelengths that pass a given point in one second
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The faster the vibration is, the higher the frequency of the wave that is produced.
Color and pitch
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The frequency and wavelength determine the color of visible light.
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The pitch is the highness or lowness of a sound.
Wave Speed
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Mechanical waves (compressional and transverse) and electromagnetic waves move at
different speeds through different materials.
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Mechanical Waves
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Which types of materials do mechanical waves travel best:
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Liquids
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Electromagnetic Waves
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Unlike mechanical waves, electromagnetic waves travel faster in a medium in
which atoms are more spread out or not present.
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Which types of materials do electromagnetic waves travel best:
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Open space(no matter)
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Liquids
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Wave Behavior
Type of wave behaviors
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Reflection
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Refraction
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Reflection
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Reflection occurs when a wave strikes a shiny object or surface and bounces off.
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An echo bounces off walls, ceiling, furniture, and people.
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A reflection occurs when light waves bounce smooth, shinny surface.
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Uneven surface = unclear image
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When light hits a smooth shiny surface, it is reflected at the same angle that it comes in.
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Angle of reflection is the angle at which light is reflected off an object.
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Refraction
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Refraction occurs when the speed of the wave changes as it passes from one substance
to another.
Refraction and wave speed
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The larger the change in speed is the larger the change in direction.
Colors from refraction
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Absorption of light
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Why do objects have color?
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Why does grass look green or a rose looks red?
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When a mixture of light waves strike an object that is not transparent, the object
absorbs some of the light waves.
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The Nature of Electromagnetic Waves
Transferring Energy
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A wave transfer energy from one place to another without transferring energy
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The sun is ____________________ miles away. How do the sun’s rays get to Earth if
there is no matter to travel through?
• Electromagnetic waves
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An electromagnetic wave is a wave that can travel through empty space and is produced
by charged particles that are in motion.
Forces and Fields
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An electromagnetic wave is made of two parts:
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A magnetic field
Electromagnetic waves
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Electromagnetic waves are produced by making charged particles, such as electrons,
move back and forth causing them to vibrate.
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A charged particle that is in motion is also surrounded by a magnetic field.
How the Electromagnetic waves are created
1. ________________________________________________________________________
2. It produces changing electric and magnetic fields that move away from the vibrating
charge in many directions.
3. These changing fields traveling in many directions from an electromagnetic wave.
Electromagnetic Wave - Wavelength and frequency
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The frequency of an electromagnetic wave is the number of wavelengths that pass by a
point in one second.
Radiant energy
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What happens if an electromagnetic wave strikes another charged particles?
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The electric field of the wave exerts a force on the particle causing it to move
The Electromagnetic Spectrum
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All the waves in the electromagnetic spectrum are produced by electric charges that are
moving or vibrating.
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The faster charges vibrate, the higher the energy of the electromagnetic wave.
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The difference between analog and digital signals
Analog vs. Digital
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Analog and digital signals are used to transmit information, usually through electric
signals.
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In analog technology, information is translated into electric pulses of varying amplitude.
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In digital technology, translation of information is into binary format (zero or one)
where each bit is representative of two distinct amplitudes.
Analog
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Technology - The analog sound wave replicates the original sound wave
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Examples – human voice, analog electric devices
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Memory - Stored in the form of wave signal
Digital
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Data Transmission- No interference when sending signals
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Examples- Computers, CDs, DVDs, and other digital electronic devices.
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Memory- Stored in the form of binary bit
Advantages of digital signals
1. Signals do not get interference
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3. __________________ can be encrypted so that only the intended receiver can decode it
( secure telephone etc.)
What are some ways that you talk to your friends?
Digital ways of communication
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There are two primary ways in which information is shared digitally:
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Using Radio Waves
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Radio waves are used to send and receive information over long distances.
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Advantages of radio waves:
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Do not interact with humans
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Objects that use radio waves to send information:
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Cell phones
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Computers
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Radio
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……plus many more
Using fiber optics
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A fiber-optic cable is made up of 100 or more incredibly thin strands of glass or plastic
known as optical fibers.
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Hook your computer up to a laser, which would convert electrical information
from the computer into a series of light pulses.
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Fire the laser down the fiber-optic cable. After traveling down the cable at the
speed of light, the light beams would emerge at the other end.
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Advantages of fiber optics
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Less signal degradation
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Uses less power
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