# Chapter 17 & 18 Waves.

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Chapter 17 & 18 Waves

Mechanical Waves Disturbance in matter that carries energy from one place to another Medium: what a wave travels through Can be a solid, liquid, or gas Created when source of energy causes vibration to travel through a medium

Transverse Waves Causes medium to vibrate at right angles to direction of wave Travels left to right Crest: highest point above rest position Rest: before wave Trough: lowest point below rest position

Longitudinal Waves Vibration of the medium is parallel to direction of wave Vibration is a back and forth motion Ex: slinky, P-wave (earthquakes)

Rarefaction: particles are more spread out
Compression: particles in a medium are spaced close together

Surface Waves Travels along a surface separating two media
Carries energy from left to right Ex: ocean waves

Properties of Mechanical Waves
Frequency and period Periodic motion: repeats at regular time intervals Period: time for one complete cycle Frequency: number of complete cycles in a given temperature Measured in hertz (Hz): cycles/second Equals frequency of vibrating source producing wave

Wavelength Distance b/w point on 1 wave and same point on next wave cycle Increasing frequency decreases wavelength

Wave Speed Speed (m/s) = wavelength (m) x frequency (Hz)
Speed can change if in a new medium Wavelength is inversely proportional to frequency Longer the wavelength, shorter the frequency Shorter the wavelength, longer the frequency

1. The musical note A above middle C has a frequency of 440 Hz
1. The musical note A above middle C has a frequency of 440 Hz. If the speed of sound is known to be 350 m/s, what is the wavelength of this note? 2. A certain FM radio station broadcasts electromagnetic waves at a frequency of 9.05 × 107 Hz. These radio waves travel at a speed of 3.00 × 108 m/s. What is the wavelength of these radio waves?

3. A wave with a frequency of 60
3. A wave with a frequency of 60.0 Hz travels through vulcanized rubber with a wavelength of 0.90 m. What is the speed of this wave? 4. A wave with a frequency of 60.0 Hz travels through steel with a wavelength of 85.5 m. What is the speed of this wave?

Amplitude Maximum displacement of the medium from its rest position
More the energy wave has, the greater its amplitude

Wave Behavior Reflection: wave bounces off a surface it cannot pass through Does not change speed or frequency of a wave Can flip wave upside down

Refraction: bending of a wave as it enters new medium at an angle
1 side moves more slowly than the other Changes wave direction

Diffraction: bending of wave as it moves around an obstacle or passes through a narrow opening
Increase if wavelength is large compared to size of opening/obstacle

Interference: 2 or more waves overlap and combine together
2 types: Constructive: increases amplitude 2 or more waves combine to make wave with a larger displacement Destructive: reduces amplitude Smaller displacement

Standing Waves Appears to stay in one place (does not seem to move)
Node: point that has no displacement from the rest position Destructive interference b/w incoming and reflected waves Antinode: point where a crest or trough occurs midway b/w 2 nodes Only forms if ½ or a multiple of half a wavelength fits exactly into length of a vibrating cord

Sound and Hearing Properties of sound waves: Longitudinal waves
Speed: varies in different media Travels faster in solids > liquids > gases Intensity: rate at which a wave’s energy flows through a given area Depends on wave’s amplitude and distance from sound source Measured in decibels (tenfold increase with every 10-decibel increase)

Loudness: physical response to intensity of sound
Increases as intensity increases Frequency: depends on how fast the source of the sound is vibrating Pitch: frequency of a sound as you perceive it Depends on wave’s frequency High  high pitch Low  low pitch

Ultrasound Sound at frequencies higher than most people hear
Used in sonar and imaging Sonar: determines distance to an object under water Name means “sound navigation and ranging” Imaging used in medical techniques

Doppler Effect Change in sound frequency caused by motion of the sound source, motion of listener, or both Higher as it gets closer Lower as it moves farther away

Electromagnetic Waves
Transverse waves of changing electric and magnetic fields (regenerate each other) Carry energy from place to place Electric field: exerts electric forces on charged particles

Wavelength and frequency: all waves vary
Speed = wavelength x frequency Wavelength is inversely proportional to its frequency

Electromagnetic Spectrum
Types of waves that make up the spectrum: Infrared, Radio, UV, X-Rays, and Gamma rays

Behavior of Light Transparent: transmits light (can pass through)
Translucent: scatters light (can see through material but objects not clear) Opaque: absorbs or reflects all light that strikes it (none passes through)

When light strikes a new medium, it can be reflected, absorbed, or transmitted
Reflection Smooth surface: clear, sharp image Rough surface: blurred or no image

Transmitted light Refraction: bending light wave can cause a mirage (false or distorted image)

Colors White light: made up of all colors of visible spectrum
Prism separates colors (dispersion) Shorter wavelengths refract more than longer wavelengths

Color of objects is color of light that reaches your eye
Depends on what object is made out of and color of light that strikes the object