Units 10-11 Flashcards
Mechanical waves
Waves that move through matter.
A “disturbance” with a repeating shape.
True or False: Mechanical waves are a disturbance
True
Why are waves called disturbances?
Waves cause a disturbance or a deviation in the equilibrium of the matter they are passing through.
What continues PROPOGATING waves?
Forces attempting to restore the medium to its equilibrium position.
Without restoring forces, there would be no waves.
How many types of mechanical waves are there?
2
What are the types of mechanical waves?
Longitudinal (compression)
Transverse (shear)
What is a longitudinal wave?
A wave that causes the molecules of the medium to vibrate in the SAME direction the wave is moving.
What is a transverse wave?
A wave that causes the molecules to vibrate at RIGHT ANGLES to the wave direction.
What is a compression wave?
A longitudinal wave driven by the force of pressure
What is a shear wave?
A transverse wave driven by shearing forces between molecules
What is a surface wave?
A wave that travels along the surface of a medium (like water)
True or False: Surface waves contain both longitudinal and transverse motions.
True
What kind of wave is light?
Transverse, but not shear
Example of compression wave
Sound
Why do shear waves ONLY propagate through solids?
Because when traveling through liquids, gases, and plasmas, the molecules are not rigidly bound to each other and drift away in the direction the force pushes on them.
Why do compression waves successfully pass through solids AND liquids, gases, and plasmas?
The molecules are not rigidly bound, but resist being compressed enough to provide a restoring force. They don’t drift (caused by shear forces).
What do restoring forces do?
Seek to restore equilibrium
Does the energy of the wave decrease or stay the same as it travels?
Decreases.
Crest
Places in waves of maximum forward OR upward displacement.
Upward for shear
Forward for compression
Trough
Places of maximum downward OR backward displacement.
Where are the equilibrium positions located between crests and troughs?
Halfway between them
How many properties define how particles vibrate back and forth between crest and trough?
4
What are the four properties of particle vibrations?
- Amplitude
- Wavelength
- Frequency
- Speed
Amplitude
The maximum distance a particle moves from its natural resting place.
ie. the distance between equilibrium and a crest or trough
True or False: High amplitude equals high energy
True
How does amplitude manifest in sound waves?
Loudness
Wavelength
The distance between successive repeating parts of a wave (like crests or troughs)
How does wavelength manifest in visible light?
Color
True or False: Red is a short wavelength and violet is a long wavelength
FALSE
Reverse
True or False: Longer wavelengths of sound waves produce lower tones.
True
Frequency
Measures the number of wave crests passing a particular point every second.
What is the unit of measurement for frequency?
Hertz
“oscillations per second”
How does frequency affect visible light?
It manifests as color. Red is low frequency, violet is high frequency
How does frequency manifest in audible sounds?
Higher frequencies produce higher tones, etc.
What is the range of sound frequency our ears are sensitive to?
20 to 20,000 hertz
Wave speed
The rate that the disturbance travels through the medium.
What does wave speed depend on?
The medium’s elastic properties, its density, and the type of wave going through it.
True or False: Compression waves travel faster than shear waves
True
True or False: Wave speed is INDEPENDENT of wavelength, frequency, or amplitude
True
A scream travels as fast as a whisper.
Wave speed formula
wave speed = frequency x wavelength
True or False: Wave length and frequency have an INVERSE relationship
True
True or False: It is ALWAYS true that high frequency corresponds to short wavelengths and low frequency corresponds to long wavelengths.
TRUE
What are the four characteristic behaviors that all waves have?
- Reflection
- Refraction
- Diffraction
- Interference
Reflections
Waves “bouncing” when they encounter abrupt changes in the nature or density of the medium they are traveling through.
Refraction
A wave going through a boundary (rather than reflecting off it). The change in mediums causes a change in speed and direction.
True or False: Sound waves refract through layers of air of different temperatures.
TRUE
True or False: Sound travels faster in warm air than in cool (DENSE) air
TRUE
What effect does density have on wave speed?
Density slows waves down.
Diffraction
Spreading of a wave around corners or obstacles or through an opening.
True or False: If the opening the wave is passing through is very small, the spreading will also be small
FALSE
The spreading becomes more pronounced as the opening becomes smaller
Interference
This occurs when two or more waves travel through the same medium at the same time.
Sometimes these waves add together to become greater, other times they subtract, creating smaller disturbances.
Constructive Interference
Two or more waves passing the same space/medium at the same time resulting in a LARGER amplitude than the individual waves separately.
Destructive Interference
Two or more waves passing through the same space/medium at the same time disturb it in opposite ways that cancel each other out, resulting in a SMALLER amplitude.
True or False: Other forms of energy transportation (like convection) will reflect and retract, but diffraction and interference are UNIQUE to waves.
TRUE
Standing wave
A wave characterized by a lack of vibration at certain points, between which, areas of maximum vibration occur.
In a standing wave, what is the point of destructive interference (no motion) called?
nodes
In a standing wave, what is the point of constructive interference (maximum motion) called?
Antinodes
Node
No vibration in a standing wave
Antinode
Maximum vibration in a standing wave
What is another name for the Doppler effect?
Doppler shift
Doppler Effect
A change in the observed frequency of a wave.
This occurs when the source and observer are in motion relative to each other.
Example of the doppler effect
Police siren
The way its pitch changes depending on how far away it is from you.
The amount of this frequency change is SOLELY dependent on the speed of the car.
What is a mechanical wave?
A wave that transports energy through a medium
True or False: A shear force is a sideways acting force
True
True or False: You can exert a shear wave into a liquid, gas, or plasma
FALSE
The atoms are not held in place enough for a wave to occur
What generally acts as the restoring force for a surface wave traveling along the boundary between two mediums?
Gravity
What is the best known example of a compression wave?
Sound wave
True or False: Bright light has high amplitude
True
True or False: Light is a wave
Falseish and trueish
SOMETIMES we consider it to be a wave, other times not.
What is light?
We aren’t entirely sure, but it could be a wave or a stream of particles.
How fast is the speed of light?
299,792.458 km/sec
True or False: Light diffracts
TRUE
What test proved that light has interference?
The slit test, there were two slits drawn and a small laser of light projected through. This created an alternating pattern of light and dark patches.
What did the double-slit experiment also prove?
That different colors have different wavelengths.
What is a diffraction grating?
A piece of glass or plastic upon which a large number of long parallel grooves are scratched close together. (like the slit experiment but the result is a rainbow).
What is the “luminiferous ether” or just “ether”?
The stuff that fills the universe that allows light to pass through it a a wave.
It was thought to be stiff like a solid (because light is a transverse wave) but also unresistive enough for planets to orbit through it.
Abandoned hypothesis.
Maxwell’s equations
A set of four fundamental laws, expressed mathematically, that govern electricity and magnetism and their relationship.
What did Maxwell’s equations prove?
That electricity and magnetism were different manifestations of the same interaction.
They describe the strength and direction of EMG fields at any location in space, and how the forces within those fields change when the charges move.
What did Maxwell’s equations prove about charge vibrations?
When a charge vibrates up and down, it creates an EMG field that propagates outwards as a transverse wave.
These waves travel through empty space and are not vibrations of matter.
They are varying electric and magnetic fields radiating outward from the source.
True or False: Maxwell said that light is an electromagnetic “disturbance” propagated through the field according to electromagnetic laws.
True
What is the family of waves that Maxwell’s equations predicted (and later proved)?
Electromagnetic radiation (collectively)
List the family of waves in order from low to high frequencies:
Radio waves, microwaves, infrared radiation, visible light (red to blue), ultraviolet radiation, x-rays, and gamma rays.
True or False: Ultraviolet radiation is bluer than blue, and infrared is redder than red!
TRUE
Photoelectric effect
The ejection of electrons from metals when light is shined on the metal’s surface
True or False: In the wave model of light, a wave striking the surface of a metal imparts energy to all electrons encountered.
True
True or False: The energy in a wave is given by the amplitude
True
True or False: The energy in LIGHT is given by the frequency
TRUE
Photon
A particle of light. It possesses energy, frequency, and wavelength, but not mass or charge
Planck’s equation
Energy = h x frequency
h = Planck’s constant (6.63x10^-34)
True or False: Light is brighter when each photon has more energy
FALSE
True or False: Light is brighter when it has more photons
True
True or False: Ultraviolet photons hold enough energy to eject electrons in cases where red photons do not.
True
What does AM stand for in AM radio?
Amplitude modulation
What does FM stand for in FM radio?
Frequency modulation
What is a pixel?
A tiny electronic light detector
Wave-particle duality
Possessing both wave and particle characteristics
What is electromagnetic radiation
all radiation associated with accelerating electric charges
The family
True or False: Electromagnetic radiation can EXERT FORCES on charged objects
True
True or False: Electromagnetic radiation can transfer energy from one place to another.
True
True or False: All kinds of light travel the same speed while in a vacuum.
True
I change direction when I change what material I am traveling through. What am I?
Both a wave and a particle
If I’m sent straight towards a pair of openings that are a bit larger than I am, spaced a bit farther apart than my size, I can only be found directly behind one or the other of the openings. What am I?
Particle
If I’m sent straight towards an opening that is a little bigger than I am, I can be found both directly behind the opening, and for a good distance to either side. What am I?
A wave
What would happen if the electroscope had a positive charge placed upon it (rather than a negative charge) and then visible light and ultraviolet light were shone on the electroscope?
Neither the visible light nor the ultraviolet light would discharge the electroscope.
What will I see in the double-slit experiment if I put some sort of detector at one of the slits that will permit me to see which slit each photon goes through?
Particle pattern
