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This physical science state test review covers waves, including their classifications, properties, and behaviors, as well as an introduction to electromagnetic waves and their interaction with matter.
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Physical science state test review P.8.6.1-8
Waves • Rhythmic disturbances that carry energy without carrying matter are called waves • Often called vibrations • Analogy: a line of people passing a ball – only the ball moves & not the people • Two categories of waves: • Mechanical waves use matter to transfer energy • Electromagnetic waves transfer energy without using matter
Mechanical Waves • The matter in which mechanical waves travel through is called the medium • Mechanical waves can be: • Transverse waves: causes matter to move up & down or back & forth at right angles to the motion of the wave. • Ex. Water waves • Compressional / longitudinal waves: matter in the medium moves forward & backward in the same direction as the motion of the wave. • Rarefaction is when particles are farther apart & compressions is where particles are squeezed together • Ex. Sound waves: sound is caused by colliding air molecules • No sound in space
Wave Properties • Amplitude: Measures the distance a wave travels from its original position • Relates to the amount of energy a wave carries • Higher amplitude causes Brighter light & lower amplitude causes dim light • Higher amplitude causes louder sound & lower amplitude causes softer sound • Tsunami verses a ripple
Wave Properties • Wavelength: measures the distance between two identical points on a wave • Crest to crest, trough to trough, compression to compression • Frequency: measures how many waves pass a particular point over a specific amount of time • Measured in Hertz • Higher the frequency the higher the pitch of a sound
Wave Properties • Wave Velocity (speed): the distance a wave travels in a given amount of time • Waves move at different speeds through different mediums • Mechanical waves travel faster in solids than in liquids or gases because particles are closer together • Electromagnetic waves travel fastest in gases slowest in solids • Speed of sound waves through water are is 343 meters/second, but through glass it is 5,640m/s • Speed of light though air is 300 million miles/second
What are Electromagnetic Waves? • Form of energy that travels at the speed of light • uses electric and magnetic fields • Can travel through a vacuum • Type based on 2 Characteristics • Wavelength • Frequency • Electromagnetic Spectrum is a collection of EM waves of all known frequencies
The shorterthe wavelength, the higher the frequency • The longer the wavelength, the lower the frequency
The EM Spectrum • The only part of the EM spectrum that we can see is visible light.
The EM Spectrum • Other EM waves include: radio waves, microwaves, UV light, and x-rays. • In empty space, all of these waves travel at the same speed. This speed is referred to as the speed of light, and is about 300 million m/s. • Light travels through space, but also travels through some mediums.
What is Light • Light is electromagneticradiationthat we can see. • The particles of EM radiation are called photons. • The frequency of light waves depends on the amount of energy carried by a photon of light. • Light can travel through space and some matter.
What is Light • Light is either luminous or it is illuminated. • Luminous objects, such as the sun or a flame, emit or release light. • The moon does not emit light, it reflects it. So it is illuminated.
Behavior of Light Waves • The moon is lit because it reflects light from the sun. Reflectionis the bouncing of a wave off a surface. • A dark cave is dark because there is no light to reflect off any objects.
How does matter interact with light? When light interacts with matter, many common effects appear such as color, reflections, and rainbows. 3 Forms of interaction of light with matter: • Matter can transmit light • Matter can absorb light • Matter can reflect light
Transmission of Light • Matter that transmits light is transparent • Air • Water • Glass • Objects can easily be seen through these transparent materials. • Translucent materials transmit light but do not let the light straight through.
Transmission of Light • When light is translucent, it isscattered in many different directions. • As a result, you can see light through translucent materials, but objects look distorted, or fuzzy.
Absorption of Light • Absorption is the transfer of light energy to matter. Opaquematerials do not let light pass through them. • Instead, they either reflect or absorb light. • When light enters a material but does not leave it, the light is absorbed.
Reflection of Light • Reflection is when light bounces off of an object. • Light bounces at an angle equal to the angle at which it hit the surface. • The Law of Reflection states that when a wave is reflected from a surface, the angle of reflection is equalto the angle of incidence.
Reflection of Light • What happens to a light wave, like a flashlight, when it interacts with a pane of glass?
Reflection of Light Write a sentence describing how the Law of Reflection applies here.
Refraction of Light • We know that light can speed up or slow down and it travels from one medium to another. When that happens, light can actually change its direction. • Refraction is the change of direction of a wave as it passes from one medium to another. • Example: from water to glass to air.
Using Mirrors • Any surface that reflects light and forms images is a mirror. The type of image depends on whether the reflecting surface is flat or curved. • Plane Mirrors • “Plane” means flat, so a plane mirror has a flat reflecting surface.
The diagram only shows a few rays, but there is an infinite number of rays involved. • The image formed is the same size as the object, but it is a virtual image. • Your brain perceives the object to be in the place where the object is not. Plane Mirrors
Not all mirrors are flat. Mirrors that curve inward are called concave. • A concave mirror is shaped like the inside of a bowl. • This type of mirror forms either real or virtual images, depending on where the object is placed relative to the focal point. • The focal point is the point in front of the mirror where the reflected rays meet. • Concave mirrors are used behind car headlights. Concave Mirrors
A convex mirror, diverging mirror, or fish eye mirror is a curvedmirror in which the reflective surface bulges toward the light source. • Convex mirrors reflect light outwards, therefore they are not used to focus light. ... The image is smaller than the object, but gets larger as the object approaches the mirror. Convex Mirrors
Matter Scatter Light can pass through a transparent medium, and that medium can also change thepropertiesof the light. Light travelsfaster in a vacuum and slows when it travels through a medium, like water. Light only travels three-fourths as fast in water.
Refraction of Light • Light changes direction when it leaves the water, making the straw look broken. • It changes direction because the speed of the light changes as it travels through air, water, and glass.
Scattering of Light • You can’t see a beam of light shining through clear air. But if a beam of light shines through fog, thelight scattersin many directions. Some of that light enters your eye, and you can see the beam.
Why do we use Lenses? • A lens is a transparentobject that has at least one curved side that causes light to change direction. • Most light passes through the lens because it is a transparent material.
Using Lenses Thegreaterthe curve of the lens, the more light refracts. The direction of the refraction depends on whether the lens is curved inward, or outward (concave or convex).
A convex lens, like a magnifying glass, is thicker in the middle than the edges. The curve of the lens refracts the light inward and converges the light rays. So the magnifying glass make objects appear larger. Convex Lens
Light rays that pass through a concave lens, diverge, or spread out. A concave lens is thinner at its center than at its edges. Light enters, refracts, and diverges (or spreads out). • You see virtual images that are smaller than the actual object. Concave lenses are used to correct short-sightedness (myopia). They help to focus the image on the retina, making it clearer. Concave Lens
Prisms • As white light passes through a glass, called a prism, each wavelength of visible light refracts as it enters and again when it leaves. • Because each color refracts at a different angle, the colors are separated and spread out in the color spectrum. • ROYGBIV
How do rainbows appear? Rainbows form when water droplets act like prisms and refract light. Each wavelength of light refracts as it enters the droplet of water and again as it leaves it. The effects is the separate colors that we see in the form of a rainbow.
Other Wave Interactions with Matter • Diffraction is the change in direction of a wave when it travels around an object , or spreads out after it travels through an opening.
What is Sound • Sounds you hear are produced by sound waves. • Sound waves are longitudinal (compression) waves that can only travel through matter. Remember, light can travel through space and matter.
Where does sound come from? • Every sound comes from a vibration. • A vibration is a rapid, back and forth movement that can occur in all states of matter: solids, liquids, and gases.
Where does sound come from? • When you pull on a guitar string, you transfer energy to the string. • When you let go, the string snaps back and vibrates. • The vibrating guitar string collides with air moleculesand transfers energy to them. • This causes a disturbance in the air that carries energy outward from the guitar string as a sound wave.
How does sound travel? • Sound waves must travel through a medium: a solid, liquid, or a gas. You mostly hear sound waves through air, but they can also travel through water, wood, metal, and brick.
How we hear sound? • Sound is a compression wave which travels through the air through a series of compressions and rarefactions. • If you touch a speaker, you can feel it vibrateas it produces sound. With each vibration, the speaker pushes air particles forward leading to sound. The speaker moves forward and back with each compression and rarefaction.
Anatomy of a sound wave • In a longitudinal (compression) wave, the matter in the wave moves back and forth parallelto the direction of the wave
Compression or Longitudinal wave On a compression wave the area squeezed together is called the compression. The areas spread out are called the rarefaction. The wavelength is the distance from the center of one compression to the center of the nextcompression.
Energy of Sound Waves • Amplitude is a measurement of the energy of sound. • The energy of a sound wave depends on the amount of energy that caused the original vibration. • As the energy of a sound wave increases, the amplitude increases.
Intensity of Sound • The unit decibel (dB) describes theintensity and loudness of sound. A loud sound can make an eardrum vibrate so hard that it tears.
Frequency of Sound • Frequencyof sound is the number of wavelengths that passa point each second. • Measured inHertz (Hz). 1 Hz = 1 wave/second. • Pitch is the perception of a high or low sound. • Human ear can detect sounds 20-20,000 Hz. Beyond 20,000 Hz is called ultrasonic. .
Resonance • when one object vibrating at the samenatural frequency of a second object forces that second object into vibrational motion. • The word resonance comes from Latin and means to "resound" - to sound out together with a loud sound. • Resonance is a common cause of sound production in musical instruments.
Resonance Resonance can shatter a glass when a sound frequency is applied to the glass that is equal to the frequency of the glass when it vibrates https://www.youtube.com/watch?v=BE827gwnnk4
Overtone-higher frequency at which objects vibrate. Sound InterferenceWhen sound waves overlap, interact, and combine to form a new wave. Fundamental- the lowest frequency at which a material naturally vibrates. Objects vibrate at both a fundamental and and overtones. The interference of these waves produces sound.
