WAVES
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Help!
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| What does a wave transfer? | momentum and energy from one point to another
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| Can waves transfer matter? | NO
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| Relate v, f, and lambda | v = f * lambda
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| What are the types of mechanical waves? | transverse and longitudinal
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| transverse wave and examples | medium displaced perpendicular to wave propagation (light and EM radiation)
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| longitudinal wave and example | medium displaced parallel to wave propagation (sound)
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| What is the final displacement of a longitudinal wave? | 0 --> moves back and forth but still 0
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| What affects velocity? | MEDIUM
1.) forces between molecules
2.) density of particles in medium
--> stronger forces, greater restoring force, faster to participate in anther compression wave, faster propagation
--> velocity constant for a string
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| What affects velocity | 1.) medium's resistance to change in shape (elasticity)
2.) medium's resistance to change in motion (inertia)
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| What kind of string moves fastest transverse wave? | tense and light
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| Why does velocity increase with temperature for a gas? | Greater the temperature, greater the random velocity, greater the sound wave velocity --> air particles move more and allow better propagation of sound waves
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| Is density a function of temperature? | YES --> volume changes
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| How does the speed of a sound wave increase / decrease? | -increases: higher stiffness (resistance of an elastic body to deformation) and higher pressure
-decreases: density
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| Compare speed of sound in solid, liquid, gas | solid > liquid > gas
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| Does sound wave travel faster in water or air? | water --> water is denser but has a greater bulk modulus
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| What is the velocity of sound waves in a gas limited by? | average speed of molecules within that gas
--> sound waves move faster through hot gases than cold gases
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| surface waves | "gravity waves" --> gravity is elastic part
-mass / density of liquid does not change rate at which surface wave rises and falls
-velocity is not changed by density of liquid
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| Why do waves move faster at higher depths? | higher depths have higher pressure
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| What happens in a dispersive medium for velocity? | velocity related to frequency and increases with wavelength
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| What is power? | rate at which wave transfers energy aka intensity
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| What do frequency and amplitude depend on? | wave source
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| What do density and velocity depend on? | medium
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| What does energy per photon depend on solely? | wavelength NEVER amplitude or intensity
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| Decibals equation | B = 10 log (I / Io)
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| Decibals rule | If intensity increases by a factor of 10, decibals increase by addition of 10 decibals
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| What do constructive and destructive interference have in common? | waves have same frequency
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| What are beats? | two waves with slightly different frequencies are superimposed
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| When a wave transfers from one medium to the next, what happens to wavelength, amplitude, and frequency? | smaller amplitude, wavelength changes and the frequency remains the same
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| What happens when wave reflects off a denser medium? Original and new wave | Original wave is inverted 180 degrees and new wave continues along in present orientation with same frequency, smaller amplitude, different wavelength
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| What happens when wave reflects off a less dense medium? Original and new wave | Original upright and new wave also upright with same frequency, smaller amplitude, different wavelength
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| What is beat frequency? | f2 - f1
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| What is the first harmonic def and aka? | -fundamental harmonic
-longest wavelength that can be generated
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| Another name for second harmonic? | 1st overtone
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| What is node? | areas with no vibration found at a fixed end
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| What is antinode? | area where amplitude is largest
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| Discuss wave speed in a uniform medium. | Always Constant!!
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| Relate wavelength, length of string, nodes | wavelength = 2L / n
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| Relate frequency, nodes, velocity, string length | f = nv / 2L
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| Relate period, length, node, velocity | T = 2L / nv
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| What can increase the amplitude and energy of a system? | apply vibrating force with frequency that matches natural frequency of a system
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| Resonance frequencies for open pipe on both ends (1,2,3) | L = lambda / 2 ; L = 2lambda / 2 ; L = 3lambda / 2
(count nodes)
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| Resonance frequencies for closed pipe on both ends (1,2,3) | L = lambda / 2; L = 2lambda / 2; L = 3lambda / 2
(count antinodes)
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| Resonance frequencies for pipe open on one end (1,2,3) | L = lambda / 4 ; L = 3lambda / 4; L = 5lambda / 4
(count complete nodes and antinodes)
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| What can't sound waves travel through? | vacuum
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| Go from 60 dB --> 20 dB, how much does intensity change by? | 10,000
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| General rule of thumb relating distance, intensity, and dB | Every time distance from source increases by a factor of 3, intensity drops by a factor of 10, dB decreases by 10
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| What creates the Doppler Effect? | waves are unaffected by speed of source that produces them
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| Formulas for Doppler Effect? | delta f / fs = v / c
delta lambda / lambda(s) = v/c
-v = relative velocity
-c = wave velocity
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| What do you do with velocities when source and observer are moving in same direction? | subtract
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| What do you do with velocities when source and observer are moving in opposite directions? | add
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| What happens when relative velocity brings source and observer closer? | wavelength decreases, frequency increases
-add delta f to f(s)
-subtract delta wavelength from wavelength (s)
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| What happens when relative velocity brings source and observer farther? | wavelength increases, frequency decreases
-subtract delta f from f(s)
-add delta wavelength to wavelength (s)
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| blue shift | when source and observer move closer to each other
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| red shift | when source and observe move apart
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| What happens when objects move in same direction at same speed? | no doppler effect
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| Mechanical waves ONLY transport_____? | energy
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| Within still air, when sound bounces off an imperfect reflector, what remains constant? | speed
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| Light speeds up / slows down when passing into something with higher "n". | slows down (both must be solids, liquids, gases)
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| Sound speeds up / slows down when passing into something with higher "n" | speeds up --> speeds up with elastic, stiff bonds
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| What creates a faster wave? | greater elasticity
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| What type of a wave is an EM wave? | transverse
--> electric and B-fields are oscillating at right angles
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| When light goes from air to a medium of higher index, does velocity, wavelength, or frequency stay the same? | frequency
-velocity slows down and wavelength decreases
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| When sound goes from less dense to more dense material, does it speed up or slow down? | slow down
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| Within a uniform medium, what always remains constant for a sound wave? what changes? | -velocity is ALWAYS constant and frequency
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| Why do sound waves travel slower in more dense material? | When comparing 2 solids, 2 liquids, etc, speed of sound decreases with increasing density
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| What does speed of sound depend on? | -resistance to compressibility of the medium (elasticity)
-density
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| What is wavelength? | length to finish one complete cycle
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| What is frequency? | number of oscillations per second
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| Generally, what remains constant for light vs. sound? | frequency vs. speed
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| What creates rainbows? | refraction by water droplets
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| Do standing wavs propagate? | NO
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| For EM waves, amplitude and intensity increase what? Do they change energy per photon? | -overall energy of EM wave
-does NOT change energy per photon
--> depends on wavelength
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| What is formula for angular frequency? | w = 2*pi*f
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| When waves are in phase, how many degrees are they apart? | 0 or 360 degrees
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| When waves are out of phase, how many degrees are they apart? | 180 degrees
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| Hooke's Law | F = -k * x
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| PE and KE of a spring | PE = 1/2kx^2
KE = 1/2mv^2
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| At the equilibrium position, describe x, PE, KE, and a. | x = 0, PE = 0, KE = max, a = max
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| At max displacement, describe x, PE, KE, and a | x = max, PE = max, KE = 0, a = 0
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| Period of a pendulum | T = 2*pi(square root of L/g)
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| Period of spring | T = 2*pi(square root of m/k)
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| For ANY wave to go from one medium to another medium, what remains constant? | frequency!
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| Through a prism, does a longer wavelength travel faster or slower? | faster
--> freq stays constant!
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| Through a prism, does a shorter wavelength travel faster or slower? | slower
--> freq stays constant!
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| When is Doppler effect produced? | anytime source moves relative to the receiver
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| What creates higher pitch? | higher frequency
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| Original Doppler Equation | fo = fs [c+/-vo // c+/-vs)
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| Source and observer both moving toward each other | fo = fs (c+vo / c-vs)
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| Source and observer both moving way from each other | fo = fs (c-vo / c-vs)
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| In dampened harmonic motion, does frequency and period stay the same? | yes
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| In dampened harmonic motion, what decreases? | energy diminishes over time
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| What is a period? | time to complete one full cycle (return to original position)
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| If no force is acting on a spring, then what state is it in? | equilibrium
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| Under dampened harmonic motion, does speed decrease? | YES
--> lose energy --> lose KE and PE --> KE decrease, velocity decrease
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| Hooke's Law | F = -Kx
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| In what direction does the force of a spring act in terms of displacement? | opposite
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| PE of a spring | 1/2 kx^2 = PE
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| When is tension greatest in a pendulum? | bob points down
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| What is restoring force for a pendulum? | F = -mgsintheta
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| PE of a pendulum? | U pendulum = -mgL (1 - costheta)
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| As a beat frequency gets smaller, does it become more or less noticeable? | more noticeable
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| With an oscillating particle non-harmonic, where is the speed fastest? | equilibrium position
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| With second harmonic mode oscillation, where is wave speed the fastest? | antinode
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| With second harmonic mode of oscillation, where is speed of string the fastest? | antinode
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