Ch 17 18 notes WAVES Electromagnetic spectrum What

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 Rarefaction-area where particles in a medium are spread out

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

• Crest-highest point of the • • wave above rest point Trough-lowest point below rest point 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) • Period-time it takes for 1 wavelength to pass a point (Increasing Frequency = period decreases)

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

Wave Movements

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

Wave Speed One end of a rope is vibrated to produce a wave with a wavelength of 0. 25 meters. The frequency of a wave is 3 hertz. What is the speed of the wave?

Wave Speed • Wavelength = 5 m • Frequency = 15 Hz • 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, *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

Principle of superposition Complete Constructive Partial Constructive

Principle of superposition Complete Destructive Partial Destructive

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 (d. B)

FYI! • Prolonged exposure to • • any noise above 85 decibels (d. B) 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.

Sound Pitch – 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 • Higher pitch, higher frequency as object approaches • Lower pitch, lower frequency as sound source moves away

STAR Questions • What kind of wave is this? – Transverse vsdfgsdhgfgf • 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

LIGHT WAVES

Electromagnetic radiation • Transverse waves • Do not need a medium

Radio Waves • a) low frequency • b) long wavelength • c) low photon energy

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

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

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

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

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 lowest photon energy • radio waves