Waves Flashcards
What is a wave’s amplitude?
The amplitude of a wave is its maximum displacement from its equilibrium position
What is a wave’s frequency?
The number of complete waves that pass a point per second
What is the period of a wave?
THe length of time taken for one complete wave to pass a given point
How are frequency and period linked?
f = 1/T
What is wavelength?
Distance between the same point on 2 adjacent waves
What is the equation for wave speed?
v = fλ
Describe a longitudinal wave
Particle oscillations are parallel to direction of the wave’s motion
Consists of rarefactions (low pressure regions), and compressions (high pressure regions)
Describe a transverse wave
Particles oscillations are perpendicular to the wave’s motion
Consists of peaks (max positive displacement) and troughs (max negative displacement)
What is a progressive wave
A wave that transfers energy from one point to another without any transfer of matter
What is a standing wave
A wave that stores energy instead of transferring it from one place to another
What is path difference a measure of
How far ahead one wave is compared to another
What is a wave’s phase
A measure of how far through its cycle the wave is. Usually measured in radians 1 cycle = 2π
What is the phase difference between 2 waves at a given point
The difference between 2 waves at a given point
What happens when 2 waves meet
Interference occurs
What happens when 2 waves meet in phase
They will interfere and undergo constructive interference
What happens when 2 waves meet in antiphase
They will interference and undergo destructive interference
How is a standing wave formed on a string
A wave reflects from a closed end meaning 2 identical waves are travelling in opposite directions down the same string
At points where the waves meet in phase, constructive interference occurs and an antinode is formed
At points where waves meet in antiphase, destructive interference occurs and a node is formed
What is a node
A point of minimum displacement
What is an antinode
A point of maximum displacement
What factors does the speed of a transverse wave on a string depend on
Time period
Mass per unit length of string
State the equation used to calculate speed of transverse wave on a string
v^2 = T/μ
What is the equation used to calculate intensity
I = P/A
What is the refractive index of a material through which light travels a speed of ‘v’
n = c/v
State the equation linking refractive indexes and angles at an interface in 2 different mediums
n1 sinθ1 = n2 sinθ2
What is the critical angle
The angle of incidence for which the angle of refraction is 90° and all the light passes along the boundary between the mediums. Beyond this angle all light will be reflected.
State the equation used to calculate critical angle
sinC = 1/n
What is TIR
Where all light is reflected back at the boundary between 2 mediums. It occurs when the angle of incidence is greater than c
What is the focal point of a converging lens
The single point where the parallel rays of light entering the lens converge to
What is the focal length of a lens
The distance between the centre of the lens and the focal point
What is the equation for power of a lens
Power = 1/ focal length
How do you calculate the total power of a combination of thin lens
P = P1 + P2 + P3…
What is a real image
An image that can be projected onto a screen and is always inverted after light has met at a focal point
What is a virtual image
Virtual images are the consequence of light appearing to meet at a point. They cannot be projected onto a screen.
State the equation for magnification of an image
Magnification = Image height / Object height
What is plane polarisation
When oscillations of a wave are restricted to a single plane
What is diffraction
The spreading out of a wave as it passes through a gap
What criteria must be met for maximum diffraction to occur
The size of the gap must be the same as the wavelength of the wave
What happens if the gap is much smaller than the wavelength of the wave
The wave will be reflected
State the diffraction grating equation
nλ = dsinθ
What does electron diffraction provide evidence for
The wave nature of electrons. It suggests that particles have wave properties.
Describe the diffraction pattern produced by electrons
Concentric circle of a bright and dark fringes from a central bright point
If electrons didnt have a wave nature, describe the pattern that would be produced when they pass through a slit
The electrons would be unaffected by the gap and pass straight through. A single bright region would be formed
What is the name given to the wavelength of a particle
De Broglie wavelength
What 2 factors does the de Broglie wave length depend on
Mass
Velocity
State the equation for de Broglie wavelength
λ = h/mv
h is Plank’s constant
What can mv be replaced with in the de Broglie equation
momentum
What is the basic process of a pulse-echo technique
A wave pulse is emitted
It is transmitted and reflected at the boundary between 2 mediums
The returning wave (echo) is detected
The speed and time are used to calculate distance to the object
Suggest 2 things that may limit the amount of information that can be obtained by a pulse-echo technique
The wavelength of the radiation
The duration of the pulse
What are the 2 models that can be used to describe EM radiation
Wave model
Particle model
Which model does the photoelectric effect provide evidence for
The particle model
Outline the photoelectric effect
Light is shone on a metal plate
IF the light has a high enough frequency, electrons are emitted from the metal surface
If the frequency is too low, no electrons are emitted
What are particles of light used to explain the photoelectric effect called
Photons
How do you calculate the energy of a photon
E = hf
Explain how a photon can liberate an electron
One photon interacts with one electron and transfers all its energy to it. If this energy is greater than the metal’s work function, the electron will have sufficient energy to be released
What is threshold frequency
A metals threshold frequency is the minimum frequency that a photon required to liberate an electron from its surface
If the intensity of light being shone on a metal increases, how does the energy of the photoelectrons change
The energy remains unaffected. An increase in intensity means more photons per area and so more photoelectrons are emitted
Why are photoelectrons emitted with a range of kinetic energies
Electrons are at different depths in the metal and so require different amounts of energy to be liberated. The excess energy from a photon once an electron has been liberated, is the kinetic energy of the electron
State the equation for the minimum kinetic energy of a photo electron
1/2 mv^2max = hf - Φ
What is the conversion factor between eV and J
1eV = 1.6x10^-19 J
What happens when electrons transition between energy levels
If electrons move to a higher energy level, radiation must be absorbed
If electrons move to a lower energy level, radiation is emitted
Why can only certain frequencies of radiation be absorbed by an atom to cause an electron transition
The electron can only exist in discrete energy levels. The energy of the photon absorbed must be the exact same amount of energy required to cover the difference between the two discrete energy levels
What is the difference between a base unit and a derived unit
A base unit is one of 7 fundamental units. A derived unit is derived from multiplication or division of units
A unit is a measure of quantity
What is the order of the scale units
Pico x10^-12 Nano x10^-9 Micro x10^-6 Milli x10^-3 Centi x10^-2 Kilo x10^3 Mega x10^6 Giga x10^9 Terax10^12
What is the difference between independent and dependent variables
Independent- what you change in an investigation and normally cause the effect on the dependent
Dependent- what is observed/measured
What is the difference between precision and accuracy
Precision is how consistent results are.
Accuracy is how close the results are to the true value
What is the difference between error and uncertainty
Error is the difference between the measurement and the true value
Uncertainty is the interval within which the true value can be considered to lie within a given level of probability
How do you calculate % uncertainty
uncertainty of measurement/measurement (x100)
How can you tell if a value is an anomaly
If it does not follow the pattern of results
What happens to the absolute uncertainty when you add/subtract/multiply or raise to a power?
Add/subtract: add uncertainties
Multiply: multiply uncertainty by constant
Raise to a power: raise uncertainty to same power
What happens to the % uncertainty when you add/subtract/multiply or raise to a power?
Add/subtract: add % uncertainties
Multiply: doesn’t change
Raise to a power: multiply by index
What is the difference between repeatable and reproducible
Repeatable measurements are when similar results can be obtained by students from the same group using the same method
Reproducible measurements are when similar results are obtained by students from different groups using different methods/apparatus
How can validity be improved
Control more variables
Use more precise measuring equipment
Obtain more results to reduce uncertainty
What is the difference between systematic and random errors
Random errors are caused by unpredictable changes in the investigation, often caused by the environment or irregular changes. Usually impact precision
Systematic errors are continuous errors throughout, often caused by equipment. Usually impacts accuracy
What is the density of a material
The density is the mass per unit volume
What is the equation for density
Density = mass/volume
What is the unit of density
kgm^-3
When an object is submerged in a fluid, what determines the upthrust that acts on it
Upthrust = weight of fluid that it displaces
What determines whether an object floats or sinks
The balance between the weight and upthrust of the upthrust. If weight > upthrust, the object will sink
Why will a uniform object, with a density greater than that of the fluid it is submerged in, always sink
Upthrust = Weight of fluid displaced
Max upthrust = fluid density x object volume x g
Object weight = object density x object volume x g
If object density >, the weight will always be greater than upthrust and the object will sink
What objects does Stokes’ Law apply to?
Small and spherical in laminar flow
What does Stokes’ law calculate
The viscous drag force that a small spherical object experiences at low speeds in a viscous fluid wuth laminar flow
State the equation for Stokes’ Law
F=6πrηv
What is elastic deformation
When an object returns to its original shape once the deforming forces are removed
What is plastic deformation
When an object no longer returns to its original shape once deforming forces are removed. It will be permanently deformed
What is Hooke’s Law
The extension of an elastic object is directly proportional to the force applied, up to its limit of proportionality
What is the limit of proportionality
The point beyond which the force applied and extension are no longer directly proportional to each other
What is the elastic limit
The point beyond which the object will no longer elastically deform, and instead plastically deforms
What is the equation for Hooke’s Law
F = kΔx F = force applied (N) k = stiffness constant Δx = extension (m)
What is mechanical stress
The force experienced by an object per unit area
What is the equation for stress
Stress = F/A
What is the unit for stress
Nm^-2
What is the equation for strain
Strain = ΔL/L
What is the unit for strain
It is unitless as it is the ratio of 2 lengths
What does the Young’s Modulus of a material tell you
How much force is required for a given extension, regardless of dimensions
What is the equation to calculate a material’s Young’s Modulus
Young’s Modulus = Stress/Strain
What is the unit for Young’s Modulus
Nm^-2
What is breaking stress
The maximum stress that an object can withstand before fracturing
What is the yield point
The point beyond which the object will experience a large extension without substantial force being applied
What type of energy is stored in an object that has been stretched
Elastic Potential Energy
What are the 2 equations for energy stored in a spring
E = 1/2FΔx E = 1/2kΔx^2
What does the gradient and area represent on a force- extension graph
gradient = elastic constant area= elastic potential energy in the spring
Define electrical current
The rate of flow of charge
What is the equation for current
I = Q/T
What is the unit for current
Ampere (A)
Define Voltage
Work done per unit charge
What is the equation linking voltage work done and charge
V = W/Q
What is the equation linking V, I and R
V = IR
What is Ohm’s law?
The current and voltage passing through a component is directly proportional when at a constant temperature
Describe the distribution of current in a series circuit
The current is the same at all positions in the circuit
What law is the distribution of current in a series circuit a consequence of
The law of conservation of charge
Charge cannot be created or destroyed, so in a closed loop the flow of charge must be equal throughout
Describe the distribution of current in a parallel circuit
It is split between the different branches
Current entering a branch = current leaving a branch
Explain how the conservation of charge applies to parallel circuits
Charge cannot be created or destroyed so the total charge leaving a source must equal the sum of currents in all individual branches
What law is the distribution of potential differences in a circuit the consequence of
The law of conservation of energy
Describe the distribution of potential differences in a series circuit
The total potential difference is split across all the components in a series circuit, in the ratio of their resistances
Describe the distribution of potential differences in a parallel circuit
The sum of potential differences in each branch of a parallel circuit is the same and will be equal to the potential difference of the source
What equation links power current and potential difference
P = IV
How can you calculate work done over a given time period by a component with a known potential difference and current
Combine the two equations P=W/t and P=IV
W = IVt
Describe the IV graph of an ohmic conductor
A straight line through the origin where I is directly proportional to V
Describe the IV graph of a filament bulb
An S shape with a constant gradient in the middle going through the origin
Describe the IV graph of a diode
An almost horizontal line with a slight positive gradient until part way through the positive values of V where the gradient curves upwards into a steeper positive constant gradient
Explain the IV graph of a filament bulb
Higher current causes higher temperature in the metal filament
Higher temperature causes higher KE in metal IONs so they vibrate more
This makes it more difficult for current to flow so the bulb’s resistance increases
What must be true when using the SUVAT equations of motion
Acceleration must be constant
What does the gradient of a distance-time graph represent
Speed
What does the gradient of a displacement-time graph represent
Velocity
What does the gradient of a velocity time-graph represent
Acceleration
Describe the shape of a velocity-time graph for an object travelling with uniform acceleration
If acceleration is constant, the gradient will be constant so it will be a straight line graph
Describe the shape of a velocity-time graph for an object travelling with non-uniform acceleration
The gradient (acceleration will change so will form a curve
Compare the velocity time graphs for uniformly accelerating and uniformly decelerating objects
Accelerating : positive gradient
Decelerating: negative gradient
What is a scalar quantity
A quantity with magnitude but no fixed direction
What is a vector quantity
A quantity with magnitude and a fixed direction
How is a vector represented on a diagram
As an arrow
The arrows direction shows the objects direction
The length of the arrow shows the object magnitude
What does resolving a vector involve
Splitting a vector into 2 perpendicular components
Describe the relationship between the perpendicular components of a vector
They are independent of each other
How should the components of a projectile be handled when carrying out calculations
Horizontal and vertical components should be treated separately
SUVAT should be used for each component
What three physical factors affect the resistance of a wire
Length
Cross sectional area
Resistivity
How does increasing length of a conductor affect its resistance
The longer a conductor is, the higher its resistance
No other factors are affected
How does increasing the cross sectional area of a conductor affect its resistance
The larger the cross sectional area, the lower the R
No other factors are affected
What is resistivity
A characteristic of a material that determines its resistance to flow of current
Compare the resistance of 2 conductors of the same dimensions, but with different resistivities
The conductor with higher resistivity will have higher R
State the equation for resistance using resistivity
R = ρl/A
What equation links number of charge carriers in a metal with drift velocity with current flow
I = nqvA
How does the potential along a uniform current-carrying wire cary as you move along it
The potential will increase as you move the wire
What is the EMF of a power supply
The amount of energy that is transferred to each Coulomb of charge that passes through it
What is the terminal pd of a power supply
The actual potential difference that is produced across the terminals and is provided to the circuit
Why does the EMF of a supply differ from its terminal pd
Some of the energy that is transferred to the charges is used to overcome the internal resistance of the power supply
Define internal resistance in a power supply
The electrical resistance when a current flows due to the materials within the supply itself
Describe a method to determine the terminal potential difference of a battery
Attach a voltmeter directly across the terminals of the battery when it is isolated
As no current flows, no potential is lost due to internal R so the voltmeter will read the value of the terminal pd
What is a semiconductor
A component that can change its R based on external conditions
Give 2 examples of semiconductors and what they are sensitive to
Thermistor- temperature
LDR- light
Describe how the resistance of a thermistor changes as temp decreases
As temperature decreases, R in a thermistor increases
Explain why the R of a thermistor will decrease with an increase in temperature
As temp increases, conduction electrons are liberated, meaning there are more charge carriers and current can flow more easily
Describe how the R of a LDR changes as light intensity increases
As light increases, the R of a LDR will decrease
What is a potential divider
A pair of resistors used to split the pd over them in a given ratio
What is the link between resistances and the pd in a potential divider
The pd of the circuit is split in the ratio of the resistance of the resistors
How would the pd over a fixed resistor in series with a LDR change as the light intensity increases
As light intensity increases, the R over the LDR will decrease
The fixed resistor will take a larger ration of the circuit potential and the pd will increase
Define wave front
Line joining points that are in phase
