# Wave Notes I. WAVES—a disturbance that transfers energy through matter or space. A. Energy Transfers: If a rock is dropped into the water, the kinetic.

## Presentation on theme: "Wave Notes I. WAVES—a disturbance that transfers energy through matter or space. A. Energy Transfers: If a rock is dropped into the water, the kinetic."— Presentation transcript:

Wave Notes I. WAVES—a disturbance that transfers energy through matter or space. A. Energy Transfers: If a rock is dropped into the water, the kinetic energy (KE) is transferred to the water by causing the particles of water to move which causes the neighboring particles of water to move. In this way, energy is transferred from one place to another.

B. Examples of Energy Transfer:
1. A rolling bowling ball (moving matter) transfers energy from your hand to the pins. This is NOT a wave. 2. If the pins were lined up down the alley like dominos and the energy from your hand caused the first to move, the other pins would in turn fall. This IS a wave.

II. MEDIUMS—substance or region through which a wave is transmitted.
A medium transfers wave energy but has no overall motion itself. B. Energy is transmitted from one place to another but matter does NOT move between these places.

C. Examples: What is the medium/matter?
1. Waves that can only travel through matter are called mechanical waves. Ocean waves have water for a medium. Sound waves have air for a medium.

2. Electromagnetic waves do NOT require a medium
2. Electromagnetic waves do NOT require a medium! They can be transmitted through a vacuum (space). (Remember: Heat transfer—RADIATION.)

III. TWO TYPES OF WAVES Transverse—waves in which the motion of the medium is at right angles to the direction of the wave. Examples: 1. ocean waves 2. Light 3. A cork or a bobber on a fishing line moves up and down as a wave passes because the medium (water) is moving up and down as the energy is transferred. Motion Direction of Energy

B. Longitudinal or Compression—waves consist of a series of compressions and rarefactions.
Molecules of the medium move in the same direction or parallel to the direction of the wave. * Think of a slinky being pushed or pulled. Compression–a space in a medium in which molecules are crowded together Rarefaction–a space in the medium where there are fewer molecules Examples: Sound waves are longitudinal.

IV. THREE BASIC CHARACTERISTICS OF WAVES
A. Amplitude—maximum distance the molecules are displaced from their normal rest position Amplitude indicates the energy of the wave in a transverse wave.

B. Higher energy is indicated by a tightly compacted medium in a longitudinal wave.
C. Frequency—number of complete waves or cycles per unit of time UNIT = Hertz (Hz) = 1 wave/sec Example: If you move a jump rope up and down twice in 1 second the frequency would be 2 Hz.

λ↑ f↓ or λ↓ f↑ v = f λ V. SPEED OR VELOCITY OF WAVES (v = d/t)
A. Speed of a wave in a medium depends on the properties (phase, density) of that medium. The speed through a medium is constant. B. Amplitude has NO effect on speed. C. Speed (or velocity) is determined by the number of waves passing in 1 second the length of the wave. Velocity (v) = Frequency (f) x Wavelength (λ) D. Since speed (or velocity) is constant in a given medium: if wavelength increases, frequency decreases. (Inverse relationship) v = f λ λ↑ f↓ or λ↓ f↑

v = f λ Example Problems:
1. A sound wave has a frequency of 110 Hz and a wavelength of 3 meters. What is the speed? Given: f = 110 Hz Formula: v = f X λ Solve: 110 Hz X 3 m = 330 m/s λ = 3m v = 330 m/s 2. A wave is traveling at a speed of 12 m/s and its wavelength is 3 meters. Calculate the wave frequency. Given: Formula: Solve:

3. A wave is traveling at a speed of 18 m/s and its frequency is 3 Hz
3. A wave is traveling at a speed of 18 m/s and its frequency is 3 Hz. What is the wavelength? Given: Formula: Solve: 4. If a wave is traveling at a speed of 16 m/s and has a wavelength of 4 meters, what is the frequency of this wave? Given: Formula: Solve:

Interactions of Waves VI. Waves traveling in the same medium move at a constant speed and in a straight line. However, waves interact if the waves encounter a different medium, obstacle or another wave.

Reflection—is the bouncing back of a wave after it strikes a boundary that does NOT absorb the wave’s energy. The incoming wave is called an incident wave. The wave that is bounced back is called a reflective wave. The line perpendicular to the barrier is called the normal. The Law of Reflection states that the angle of incidence is equal to the angle of reflection.

2. Refraction—is the bending of a wave due to a change of speed as a wave passes at an angle from one medium to another.

3. Diffraction—is the bending of waves around the edge of a barrier or opening. It is a result of new series of waves being formed when the original waves strike the barrier of opening.

4. Interference—is a process that produces a new wave when two or more waves arrive at the same point at the same time. The two waves can combine in 2 different ways. Constructive interference—occurs when the crests of one wave meet the crests of the other. The two waves form together in a single wave with an amplitude that is the sum of the original waves. Destructive Interference—occurs when crests of one wave meet troughs of another. The amplitude is the difference between the amplitudes of the original waves.

Sound Waves VII. Sound—a form of energy that causes molecules of a medium to vibrate back and forth Series of compressions and rarefactions—longitudinal waves ***If there are no molecules, there is no sound.

1. SPEED of SOUND a. In air, speed of sound is around 340 m/s. b. Speed increases as temperature because the molecules of the air are moving faster and bump into each other more often. c. Sound is transmitted faster in solids than liquids because these materials are more elastic. (Elastic = can return to their original shape) Sound is slowest in air.

2. INTENSITY and LOUDNESS
Intensity of sound is determined by the amplitude of the sound wave. Intensity determines loudness of sound. Intensity is measured in unit called decibel.

3. FREQUENCY and PITCH Pitch depends on how fast the molecules of a medium vibrate which depends on the frequency of waves. The number of waves passing a point in a second is called cycles per second or Hertz (Hz). High Low

c. Human ear has a range of 20 Hz to 20,000 Hz.

d. The pitch (frequency) of a sound can change if the speed of the sound changes.
Example: Your voice sounds higher pitched when you inhale helium because the sound travels faster in the helium than air! Wind instruments can go “sharp” as the temperature increases because the speed of sound increases. The wavelength (length of air column) stays the same, so the frequency must change.

4. DOPPLER EFFECT Doppler Effect—a change in frequency and pitch of a sound due to motion of either the sound source or observer If source of sound moves toward observer, waves are generated from points that are closer and closer. Therefore, waves reach the observer sooner. The observer hears more waves/second, causing higher frequency (higher pitch). If source of sound moves away, waves reach observer later (fewer waves/second), causing lower frequency. Think about the following question? What does a fire truck siren sound like? Does it sound different when it is passing you by on the road?

5. QUALITY OF SOUND Timbre—quality of sound caused by blending of pitches Example: A tuning fork has a pure tone (one frequency). Voice, strings, air columns produce tones that are blends of pure tones that account for the difference in quality. This is why 2 different instruments can play the same pitch and sound different.

6. RESONANCE Every medium has its own frequency of vibration called natural frequency. Resonance—ability of an object to vibrate by absorbing energy in its natural frequency Examples: The vibrations of a sound board of a violin The note you get when you blow into a half full bottle of soda Singer breaking a glass

7. CONSTRUCTIVE and DESTRUCTIVE INTERFERENCE
Sound waves can combine constructively and destructively. When in phase the intensity of sound is increased. When out of phase, sound is softer and “dead spots” can occur. Beats—phenomenon caused by combination of 2 waves of slightly different frequencies. This causes intensity to vary.

Light Waves VIII. Light is both a wave and particles. This contradiction perplexed scientists for many, many years. The speed of light is 3 x 108 m/sec. Sound is fast (340 m/sec), but light is faster. Light can circle the earth 27 times in one second. Scientists now believe that nothing can go faster than light. Question: Why do you think you see a flash of lightning before you hear a clap of thunder?

Red → long waves to short waves → Violet
2. VISIBLE LIGHT What we call “visible light” is made up of many different colors. Each color has a different wavelength and a different frequency. A. A prism uses refraction to separate the different wavelengths (colors) of visible light. Red → long waves to short waves → Violet

B. Colors have different energies
B. Colors have different energies. You know that different flames give off different amounts of heat. Red flames are the coolest and blue flames are the hottest. As you move from red to blue, light GAINS energy. White light is made up of all colors—that is why a white flame is the hottest! Which color has the longest wavelength? Red Which color has the shortest wavelength? Violet Which color has the highest energy? Violet

C. Visible light is a very small part of the entire electromagnetic spectrum.
Radio waves—used to transmit radio and television signals. Microwaves—used to cook food and by cell phones. Infrared—invisible heat Visible (white) light Ultraviolet light—invisible wavelengths; part of sunlight burns your skin and can cause cancer. The ozone layer protects us from most of the sun’s ultraviolet light. X-rays—used in medicine and industry. Gamma rays—the most powerful and dangerous form of radiation. Emitted by nuclear reactions, they can break chemical and nuclear bonds.

3. LENSES and MIRRORS Lenses and mirrors work opposite of each other. If a concave lens reduces, then a concave mirror magnifies. A. Concave and Convex Concave looks like the sides have caved in. Convex—the middle is bigger than the ends.

B. Lenses—work by refraction, by the light bending when moving between two substances.
C. Mirrors—work by reflection, by the bounding of light off of a shiny surface. Images in mirrors always look twice as far away as the object.

Seismic Waves IX. The movement of Earth’s plates creates stress in the rock. When the stress in the rock builds up enough, the rock breaks or changes shape, releasing energy in the form of waves or vibrations. The waves produced by earthquakes are known as seismic waves. (The word seismic is Greek for EARTHQUAKE.)

4. Seismic waves include primary waves, secondary waves and surface waves.
Primary Waves—are longitudinal waves or P waves. They move faster than other seismic waves and so arrive at distant point before other seismic waves. Secondary Waves—are transverse waves or S waves. Secondary waves CANNOT travel through liquids. Since part of the earth is liquid, S waves do NOT travel directly through Earth and cannot be detected on the other side of Earth. Surface Waves—P and S waves can be transformed into surface waves at Earth’s surface. Surface waves are a combination of longitudinal and transverse waves. Even though surface waves travel more slowly than P or S waves, they produce the most severe ground movements.

5. Seismographs—detect and measure earthquake waves
5. Seismographs—detect and measure earthquake waves. A seismograph records the ground movements caused by seismic waves as they move through the Earth.

6. Tsunami—a seismic wave or tsunami is a devastating water wave generated by an undersea earthquake.

Sonar used to find sunken ship.
F/A-18 Hornet passing through the sound barrier. Photograph taken by Navy Ensign John Gay while aboard the carrier USS Constellation, 07/07/99. Your first baby picture was taken using sonar. Sonar used to find sunken ship.

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