M3 Waves & Thermodynamics Flashcards
3 Wave Classifications
- Transverse - particles oscillate/vibrate at 90 degrees to the direction of motion of the wave
Longitudinal - particles oscillate/vibrate in the same direction as the direction of the motion of the wave
Complex - combination of longitudinal and transverse motion (particles oscillate in circular/elliptical path) - Mechanical - require a medium for wave to travel through
eg sound, earthquake, water, domino wave, heat conduction, alternating current
Electromagnetic - does not require a medium
eg radio, microwaves, infrared, visible light, ultraviolet, xrays, gamma
* all travel at c
* all EM waves are transverse - Standing/Stationary - combination of two waves moving in opposite directions, each having the same amplitude and frequency. The phenomenon is the result of interference; that is, when waves are superimposed, their energies are either added together or canceled out.
Progressive - A wave which travels continuously in a medium in the same direction without a change in its amplitude
wave
a disturbance that transfers energy from one place to another without any overall movement of matter
direction of propagation
the direction in which a wave travels
Two Types Of Graphs
- Displacement-Distance
provides a “freeze frame” of the wave at a particular moment in time
- used to determine wavelength (measure with a ruler/x-axis)
- used to determine amplitude (measure with y-axis) - Displacement-Time
shows the movement of just one part of the wave over time
- used to determine period (read off x-axis)
- amplitude (read off y-axis)
graphing longitudinal waves
on a D-D graph (since we have to graph a longitudinal wave as a transverse wave) compressions become crests, rarefactions become troughs
reflection
occurs when a wave hits a boundary between two mediums and returns into the medium from which it came
- all types of waves can be reflected
the law of reflection
angle of incidence = angle of reflection
- AoI & AoR measured between the wave (incident and reflected ray) and normal
2 Types of Reflection
Specular: when a wave reflects from a plane surface
- parallel rays reflect in the same direction
- can produce a reflected image
Diffuse: when a wave reflects from a rough surface
- rays are reflected in different directions
- parallel rays reflect in different directions
- cannot produce an image
refraction
a change in wave direction when the wave changes speed (through transition in medium)
- if a wave slows down, bend toward normal
- if a wave speeds up, bend away from normal
diffraction
occurs when a wave encounters an obstacle/aperture
- can results in various patterns being produced in the region behind the obstacle
- diffraction is a property of all waves (one of the reasons why we know light acts like a wave)
- diffraction patterns are closely linked to wave superposition
wave superposition
adding together two or more waves as they pass through each other
constructive interference
when the waves add together to produce a bigger amplitude
destructive interference
when the waves cancel to produce a smaller (or zero) amplitude
standing wave
caused when a wave meets its reflection, producing an oscillating but otherwise stationary wave
- created when 2 progressive waves travelling in different directions superpose
–> so the resultant wave has some points fixed and some points oscillating at max amplitude
- fixed points are called nodes
- points oscillating at max amplitude are antinodes
driving force
any force that adds to the oscillation
resonance
occurs in oscillating systems
- can produce large amplitudes from relatively small driving forces
- if the driving force has the correct frequency, it will cause the system to oscillate with a greater amplitude (the system is resonating)
damping
any forces that reduces the amplitude of an oscillation
natural frequency
the frequency at which a system will naturally oscillate in the absence of any driving or damping forces
driving frequency
the frequency of the force driving the oscillating system (not all systems have a driving force)
you get resonance when
the driving frequency equals the natural frequency
energy transformation and transfer in an oscillating system
- energy in a pendulum oscillates between kinetic and potential
- damping (friction) removes energy (usually to heat) so amplitude of the oscillations will get smaller
- a driving force adds energy back into the system
energy is transferred in a mechanical wave because…
… particle interactions are elastic, so kinetic energy is transferred along with momentum
we see a mirror image of ourselves in a mirror because…
… light rays preserve their order, according to the orientation of our eyes when they reflect off a mirror
parabolas have the property that…
all light rays emanating from the focus will form a parallel beam
sound waves will be refracted in the same medium if…
there is a temperature change within the medium
if a sound wave front enters a denser region in a perpendicular direction
speed and wavelength both change
frequency remains constant
compression:
rarefaction:
(pressure)
region of high pressure
region of low pressure
volume is to
pitch is to
amplitude
frequency
inverse square law
relates wave intensity to distance
- the intensity diminishes with distance because the energy has to spread over a bigger and bigger area
- the intensity is proportional to 1/r^2
examples of reflection
mirrors, sonar, echoes, ultrasound imaging
examples of diffraction
patterns formed from small apertures, rainbow colours on DVDs, sound travelling “around” corners
examples of resonance
playground swing, wine glass breaking, musical instrument
examples of superposition
waves on waves at a beach, human voice
Doppler Effect
caused when a wave source and an observer are moving with respect to each other
- when the source and observer get closer,
the wave crests bunch together & the observer frequency increases - when the source and observer are getting further away,
the wave crests are further away
the observed frequency is lower
Doppler Effect Formula (to remember which is pos and neg)
velocity of observer is POS if it’s moving TOWARDS source
velocity of source is POS if it’s moving TOWARDS the observer
An oscillating system will often have more than one natural frequency
- these natural frequencies are called harmonic frequencies/harmonics
- each harmonic corresponds to a particular wavelength of standing wave that physically fits into the system
- the lowest possible harmonic frequency is the fundamental frequency (the standing wave that has the longest wavelength possible in that system)
there is resonance if…
you have an anti-node at the open end of the pipe
effect of length on frequency (think musical instruments)
the longer the string, the longer the wavelength, the lower the frequency (inversely proportional)
effect of mass on frequency (think musical instruments)
the higher the mass, the lower the frequency (inversely proportional)
effect of tension on frequency (think musical instruments)
the higher the tension, the higher the frequency
effect of wave velocity on frequency (think musical instruments)
any increase in velocity, increase in frequency (v=fλ)
beats
a rhythmic pattern resulting from a cycle of constructive and destructive interference/superposition between two or more waves
(the beat frequency is the difference between the frequencies of the original waves)
refractive index
a measure of how much a wave slows down when it travels through a medium
vacuum is 1
air is 1.0003 (same as vacuum)
water is 1.3
glass is 1.5
diamond is 2.4
Snell’s Law
the angles of incidence and refraction can be calculated with
n₁ sinθ₁ = n₂ sinθ₂
where
n₁ = refractive index of medium 1
n₂ = refractive index of medium 2
θ₁ = angle in medium 1 (angle of incidence)
θ₂ = angle in medium 2 (angle of refraction)
white light
when we view all the colours of visible light mixed together, our eyes and brain interpret it as
dispersion
the phenomenon when white light is shone through a prism, the component colours are refracted by different amounts and separated into a spectrum
- this happens because waves of different wavelengths are slowed down or sped up by different amounts as they travel into a medium
(different frequencies have different indices of refraction in new medium)
critical angle ( θ꜀)
the incident angle that causes an angle of refraction of 90ᵒ (the refracted ray travels along the boundary between the two mediums)
total internal reflection
angles of incidence that are bigger than the critical angle reflect back into the medium and don’t refract
optic fibre
has a central core of high refractive index and an outer cladding of a lower refractive index
- as long as the angle of incidence is bigger than the critical angle at every point along the fibre, the light will continue to be reflected internally
lenses and mirrors can produce images that can be
upright or inverted
enlarged or reduced
virtual or real
by tracing the path of just a few rays,
we can predict what the object will look like to an observer
virtual image
an apparent image formed when rays diverge from a point (image appears in your brain {think mirror})
real image
an image formed when rays converge to a point - can be projected onto a screen
curved mirrors
the perfect shape for a curved mirror is a parabola
- in a parabolic mirror, parallel rays will all converge to a single point called the focus/focal point
what physical property of sound waves varies sinusiodally?
pressure
the difference in sound is all about…
the harmonics produced
A guitar string when plucked has a frequency of 700 Hz. If the tension is the string is increased what will
happen to the frequency of the emitted note? Explain your answer.
When tension increases the velocity of the wave in the string increases. The wavelength is unchanged
as it depends on the length of the vibrating string. From the wave equation we see that the frequency
will increase.
Which property of a wave does not change when it is refracted?
frequency
A car bumper sticker is red with white writing and reads, “If this sticker is blue, you are driving too fast”
Explain what this means?
This is referring to the Doppler effect. At high speeds the frequency increases which as the speed of light
is constant means that the wavelength decreases. Blue light has a shorter wavelength than red light
however this would require speeds close to that of the speed of light for this to be noticeable.
The relationship between the curvature of the lens & the focal length
The greater the curvature of the lens, the shorter the focal length
Frequency For nth Harmonic
Pipe with one open end, one closed end
fn= nv/4L
v is the speed of sound wave in air
Fundamental, Third, Fifth… (harmonic)
Frequency For nth Harmonic
Pipe with two open ends
fn = nv / 2L
v is the speed of sound wave in air
Fundamental, Second, Third…
(harmonic)
Convex lens
Converging, bends light inwards to focus
Parallel rays refracted inwards to principal focus F
Has 2 principal foci (one on each side of the lens) F and F’
Concave lens
Diverging, bends light outwards (rays can be traced to the focus)
Centre of lens
Optical centre C
Distance of F from C (distance between focus and optical centre)
Focal length f
Line through optical centre and 2 foci
principal axis
real images
light rays converge to a point
Image can be captured on a screen
Only formedby convex lenses
Virtual images
light rays diverge from a point
No rays actually come from the image
Construction rules for convex lenses (3)
- A ray parallel to the principal axis is refracted through F
- A ray passing through F’ is refracted parallel to the principal axis
- A ray passing through C travels straight on
Construction rules for concave lenses (3)
- A ray parallel to the principal axis is refracted so that it appears to come from F’
- A ray directed towards F is refracted parallel to the principal axis
- A ray directed towards C travels straight on
Images formed by a convex lens
object: at infinity
image: at F, real, inverted, diminished
Images formed by a convex lens
object: beyond 2F’
image: between F and 2F
real, inverted, diminished
Images formed by a convex lens
object: at 2F’
image: at 2F
real, inverted, same size
Images formed by a convex lens
object: between F’ and 2F’
image: beyond 2F
real, inverted, magnified
Images formed by a convex lens
object: at F’
image: at infinity
Images formed by a convex lens
object: < F’ (in between F’ and C)
image: on the same side as the object, virtual, erect, magnified
Images formed by a concave lens
object: at infinity
image: at F’
Images formed by a concave lens
object: within 2F’ (or near object)
image: between F’ and 2F’, on the same side of object, virtual, erect, diminished
calibration
the process of marking with graduations, of quantities such as degrees, for example on a thermometer
change of state
the physical process where matter changes from one state to another. examples are melting, evaporation, boiling, condensation, freezing
conduction
the transfer of energy in the form of heat from one atom to another within an object by direct contact
convection
the process of heat transfer through a gas or liquid by motion of the hotter material into a cooler region
density
mass per unit volume
SI units are kg m^-3
gas
a phase of matter where the atoms or molecules are more widely spaced than in solids or liquids and only occasional collide with one another
heat energy
a form of energy transfer among particles in a substance by means of kinetic energy of those particles
kelvin temperature scale
the temperature scale designed so that zero K is defined as absolute zero, a hypothetical temperature, where all the molecular movement stops. A change of one kelvin is the same as a change of one degree celsius
latent heat
the energy absorbed or released by a substance during a change in its state that occurs without a change of temperature
liquid
a phase of matter were atoms or molecules can movge freely while remaining in contact with one another. a liquid take the shape of its container
radiation
the emission or transmission of energy in the form of waves
solid
a phase of matter where molecules vibrate about fixed positions and cannot move to other positions in the substance. A solid has a fixed shape and volume
specific heat capacity
the amount of heat energy needeed to raise the temperatuer of one kilogram of the matieralby 1 degrees celsius/kelvin
the units are J kg^-1 K^-1
temperature
a measure of warmth or coldness of an object or substance with reference to some standard value
thermal conductivity
a measure of the ability of a matieral to transfer heat
units of k are W m^-1 K^-1
thermal equilibrium
the condition under which two substances in physical contact with each other exchange no heat energy. two subtqances in thermal equilibrium ar said to be at the same temperatuire
thermodynamics
the branch of physics which deals with temperature and heat and their relatioship to energy and work of a system
absolute zero
in particle theory,
all particle movement stops
the lowest temperature possible (-273.15 degrees C or 0K)
heat
a type of energy, measured in joules (J)
- kinetic energy of these vibrating particle
temperature
measure of the amount of heat energy per particle in a substance, the unit is K kelvin
Different objects can have the same amount of heat but different temperatures
- heating something up adds heat energy and increases the temperature
- for a given amount of heat, the actual temperature change will depend on the substance being heated
thermal equilibrium
(is the state that no net heat flows between them)
heat will flow between two connected systems/objects at different temperatures (from hot to cold)
two connected objects are at thermal equilibrium when heat no longer flows between them
methods of heat transfer
conduction: heat energy is transferred through physical contact between moving particles
convection: heat energy moves because hot, less dense liquids and gases float above their colder counterparts (in a circular motion)
radiation: heat energy is transferred via electromagnetic waves, specifically infrared radiation (only way heat can travel through a vacuum)
the specific heat capacity/specific heat
(& equation)
since different substances require different amounts of heat to increase their temperature by the same amount
the amount of heat energy required to increase the temperature of 1kg of substance by 1K is
Q=mcΔT
where, Q is the heat required (J)
m is the mass (kg)
c is the specific heat capacity (J/kgK)
ΔT is the change in temperature (can be Celsius or Kelvin)
when a substance melts,
the total energy change is equal to the latent heat of fusion plus the energy required to heat it to the desired temperature
the specific latent heat of a substance is calculated using
Q=mL
Q is total latent heat
m is the mass of the substance
L is the specific latent heat (latent heat per kg)
latent heat
heat energy required to completely change the phase of an object
latent heat of fusion
the heat required to change a substance from solid to liquid
latent heat of vapourisation
the heat required to change a substance from liquid to gas
the rate at which heat will be transferred
(rate of conduction) (measured in Watts) (Q/t) between or through an object depends on
- the temperature difference between the two ends/sides of the object
- the distance between the ends
- the thermal conductivity of the object
- the cross-sectional area of the object
k is thermal conductivity
A is cross-sectional area
ΔT is the difference in temp between one side of the object and the other
d is the width of the object
On a cold night, a woollen blanket is good at keeping you warm. Outline how the blanket keeps you warm.
The woollen blanket contains trapped air. Air is an insulator, and reduces the flow of heat by conduction. Also, the blanket reduces the movement of air, hence reducing convection losses.
A common piece of safety equipment for taking bush walking is a silver space blanket. Explain the principles of this blanket and how it might help bushwalkers who have hypothermia.
The blanket is a reflector of radiation and so reflects heat back to the body. The blanket will also reduce movement of air hence reducing convection losses.
Outline the features of vacuum flasks that keep food both hot and cold.
Vacuum flasks have a double glass silvered wall with a vacuum in between. The vacuum reduces heat loss by conduction, the silvered wall reduces heat loss by radiation. The flask also has a stopper made of an insulator to reduce convection losses.
When you touch the metal frame of a chair, it feels colder than the plastic seat. Discuss if the metal frame and plastic seat are in thermal equilibrium and if so, why you make this observation.
The two objects are in thermal equilibrium with their surroundings - that is, they are both at the same temperature. The metal frame feels colder as it is a good conductor of heat, so taking heat away from your body quickly.
When bushwalking in a cold climate, walkers are often advised to wear layers of clothes rather than one garment. Explain the reasoning of this advice.
The layers of clothes trap air in between them. As air is an insulator that reduces heat loss, and keeps the bushwalker warmer.
When swimming it is often noticeable that water is warmer on the surface. Explain the reason for this
Due to convection, hot water rises because the molecules are further apart, and hence the density of the water is less.
A type of star known as a white dwarf is the fate our Sun will face in about 5 billion years. In this stage of the Sun’s evolution, energy production has stopped and the white dwarf cools down to reach thermal equilibrium with its surroundings, in this case, space. Outline the process by which white dwarves cool down.
The white dwarf loses heat by radiation only as it is in a vacuum, hence there is no heat loss by conduction or convection.
