Ch 17 & 18 notes WAVES & Electromagnetic spectrum

What is a Wave? Waves-rhythmic disturbances that carry energy through matter/space Medium-material through which a wave can travel & transfer energy –*solid, liquid, gas, or combination

3 major types of waves 1. compressional aka Longitudinal 2. Transverse 3. Surface

Longitudinal Waves (aka compressional) - matter vibrates in same direction as the wave Propagation (travels), parallel (compression or push-and-pull waves) Ex: Primary earthquake waves & sound waves

Compression-area where particles in a medium are spaced close together Compression-area where particles in a medium are spaced close together Rarefaction-area where particles in a medium are spread out Rarefaction-area where particles in a medium are spread out

Transverse Wave -media move at right angle to direction of wave propagation Transverse Wave -media move at right angle to direction of wave propagation Wavelength Crest Wavelength Crest Amplitude Amplitude _ _ _ _ _ _ _ _ _ _ _ _ _ _ _rest point (equilibrium) _ _ Amplitude AmplitudeTrough

Crest-highest point of the wave above rest point Crest-highest point of the wave above rest point Trough-lowest point below rest point Trough-lowest point below rest point Wavelength(λ) -distance btw a point on one wave & same point on next cycle of wave. Wavelength(λ) -distance btw a point on one wave & same point on next cycle of wave.

Amplitude-max displacement of medium from its rest point, corresponds to amount of energy a wave carries (more energy = greater amplitude)

Frequency-# of wavelengths that pass a fixed point each second, measured in Hertz (Hz) (Increasing Frequency = wavelength decreases) Frequency-# of wavelengths that pass a fixed point each second, measured in Hertz (Hz) (Increasing Frequency = wavelength decreases) Period-time it takes for 1 wavelength to pass a point (Increasing Frequency = period decreases) Period-time it takes for 1 wavelength to pass a point (Increasing Frequency = period decreases)

Surface Wave- travels along a surface separating two media Ex: Ocean Waves (btw water & air)

Wave Movements

Wave speed Velocity of wave=wavelength x frequency Velocity of wave=wavelength x frequency V w = (lambda) x f V w = (lambda) x f [m/s] = [m] x [Hz] [m/s] = [m] x [Hz] Wave velocity wavelengthfrequency

Wave Speed One end of a rope is vibrated to produce a wave with a wavelength of 0.25meters. The frequency of a wave is 3 hertz. What is the speed of the wave?

Wave Speed Wavelength = 5m Wavelength = 5m Frequency = 15Hz Frequency = 15Hz Speed =? Speed =?

Star Questions Time it takes for one wavelength to pass a point Period Unit for frequency Hz Dense part of longitudinal wave compression

Reflection

Behavior of waves 1. Reflection –wave bounces off a surface that it cannot pass through –does not change speed or frequency, but wave can be flipped upside down –occurs with all types of waves

Refraction

Refraction –bending of a wave as it enters a new medium at an angle –one side of the wave moves more slowly (dependent on speed) than the other side, –one side of the wave moves more slowly (dependent on speed) than the other side, *violet light bends most

Diffraction –bending of wave as it moves around an obstacle or passes through a narrow opening –diffracts more of its wavelength is large compared to the size of an opening or obstacle

Interference –Two types 1. constructive-the waves add together 2. destructive-the waves subtract from each other as they overlap

Complete Constructive Partial Constructive Principle of superposition

Complete Destructive Partial Destructive Principle of superposition

Standing wave=that appears to stay in 1 place. Node: no movement from rest position Antinode: crest or troughs

Behavior of waves Polarization –Light w/ waves that vibrate in one plane is polarized light –Horizontal filter blocks waves vibrating on a vertical plane –Vertical filter blocks waves vibrating on a horizontal plane

Polarization

Sound (a longitudinal wave) Speed of sound depends on: 1. type of medium - solid best conductor *no sound on moon or in space 2. temperature of medium - faster at higher temps

Sound Intensity – rate at which a wave’s energy flows through a given area Loudness – human perception, measured in decibels (dB)

FYI! Prolonged exposure to any noise above 85 decibels (dB) can cause gradual hearing loss. 100 decibels - no more than 15 minutes prolonged exposure recommended 110 decibels - regular exposure of more than one minute risks permanent hearing loss without hearing protection.

SoundPitch – highness or lowness of a sound high frequency = high pitch low frequency = low pitch humans hear between 20 & 20,000 Hz Ultrasonic is above 20,000 Hz Infrasonic (subsonic) is below (thunder)

Sound Resonance – if the sound that reaches an object is at the same frequency of the object, the object will begin to vibrate at that frequency Noise pollution – includes sounds that are loud, annoying or harmful to the ear

Why do concert places usually have carpet on walls and floors?

Doppler effect change in sound frequency caused by motion of the sound source, motion of the listener, or both change in sound frequency caused by motion of the sound source, motion of the listener, or both Higher pitch, higher frequency as object approaches Higher pitch, higher frequency as object approaches Lower pitch, lower frequency as sound source moves away Lower pitch, lower frequency as sound source moves away

STAR Questions What kind of wave is this? –Transverse What state of matter is the best conductor? –Solid What 2 things affect the speed of sound? –Type of medium and temperature What type of wave is a sound wave? –Longitudinal (AKA compressional) Why is there no sound in space? –There is no medium for the sound waves Loudness is human perception of what wave property? –Intensity  Amplitude  Energy What wave property affects sound’s pitch? –frequency vsdfgsdhgfgf

LIGHT WAVES

Electromagnetic radiation Transverse waves Do not need a medium

Radio Waves a) low frequency b) long wavelength

Infrared (IR) sunlight Heat Body gives off IR

Visible Light only part of the spectrum you can see ROYGBIV

LIGHT AND COLOR In order for you to see an object, it must reflect at least a little bit of light

Ultraviolet overexposure can damage skin cells –Causes skin cancer ozone layer protects us from most UV

X-Rays can travel through skin & muscle absorbed by denser materials such as bone used for taking pictures of bones

Gamma Rays highest frequency, shortest can be used to kill cancerous cells

Light Transmission Opaque Materials-absorb or reflect all light & you cannot see objects through them

Light Transmission Transparent Materials-allow light to pass through & you can clearly see objects through them

Translucent Materials-allow light to pass through but you cannot clearly see objects through them Light Transmission

Star Questions Tell me in order the colors of the visible spectrum from longest to shortest wavelength ROYGBIV Type of em with highest frequency Gamma Type of em with the longest wavelength Radio