Please enable JavaScript.
Coggle requires JavaScript to display documents.
☢️PHYSICS COMPLETE AQA A LEVEL COURSE☢️ - Coggle Diagram
☢️PHYSICS COMPLETE AQA A LEVEL COURSE☢️
Section 6.2: Thermal Physics :fire:
Thermal Energy Transfer
Internal Energy : Equal to sum of all of the kinetic and potential energies of all its particles
2 ways to increase Internal energy of a system
Do work on it or Increase the temperature
When a substance changes state, its internal energy also changes -> this is due to potential energy of the system changing, while the kinetic energy stays constant
When at the boiling/melting point the energy gained through heating is no longer used to increase temperature rather to break bonds (increase in potential energy)
The amount of energy to change the temperature of a substance is equal to the product of mass, specific heat capacity and temperature change
Specific Heat capacity is the amount of energy required to increase the temperature of 1 kg of a substance by 1k without changing it state
Q=mcΔt
The amount of energy to change state is equal to the product of mass and specific latent heat
Specific latent heat is amount of energy required to change state of 1 kg of a substance without changing temperature
Specific Latent Heat of fusion - Solid to liquid
Specific Latent Heat of Vaporisation - Liquid to gas
Q=ml
Ideal Gases
Gas Laws
Describe the experimental relationship between pressure(p), volume(v) and temperature(T) for a fixed mass of gas.
Boyle's Law
When temperature is kept constant, pressure and volume are inversely proportional
Charles's Law
When pressure is kept constant, volume is directly proportional to absolute temperature
The Pressure Law
When volume is constant, pressure is directly proportional to absolute temperature
All the experimental Gas equations can be combined into the idea gas equation
pV=nRT
n = number of moles of a substance
Number of molecules (N) = n * Avogadro constant
This changes the ideal gas equation to pV = NkT
k =
Boltzmann constant
= 1.38*10^-23 J/mol
R =
Molar Gas Constant
= 8.31 J/K/Mol
Absolute scale of Temperature
Is the Kelvin Scale
All calculations in thermal physics are done in kelvin
K = C+273
Absolute Zero- 0k is the lowest possible temperature
Temperature where particles have no kinetic energy
The temperature at which volume and pressure of a gas are zero
Work is done on a gas to change its volume under constant pressure
Work done = pΔV
The internal energy of an ideal gas has no potential energy therefore is equal to the sum of the kinetic energies of its particles
Molecular Kinetic Theory Model
Brownian Motion
Random motion of larger particles in a fluid caused by collisions with surrounding particles
Observed through looking at smoke particles under a microscope
contributed evidence for the existence of atoms and molecules
Simple molecular Model can be used to explain the gas laws
Boyles Law : if you increase volume of a fixed mass of gas, collisions will be less frequent therefore pressure decreases.
Charles Law: when temperature of a gas is increases, Kinetic energy is gained meaning quicker movements, as pressure is kept constant the molecules move further apart meaning volume increases.
Pressure law: When temperature is increased molecules will move quicker, as volume is constant the frequency of collisions will increase, meaning pressure increases
Based on theory rather than experimental evidence.
Several Assumptions for the Kinetic Model:
No intermolecular forces
act on the molecules, The
duration of collisions is negligible
in comparison to time between collisions, The motion is
random
and they experience
perfectly elastic collisions
, the molecules follow
Newton's laws
, The molecules
move in straight lines
between collisions.
Derivation of the equation
Cube of length l, one molecule has a mass of m and is travelling to the right with a velocity of u.
1.
Molecule collides with the right wall with a velocity of u, its
change in momentum
is mu - (- mu) = 2mu
2.
The distance the molecule travels before it collides with the wall again is 2l, Therefore the time between collisions is t, where t = 2l/u
3.
the
impulse
can be calculated, which is the rate of change in momentum. As the impulse is equal to the force exerted the
pressure
can be found by dividing the impulse by the area of one of the walls: l²
F= 2mu/(2l/u) = mu²/l
1 more item...
4.
There are many molecules in the cube, the total pressure is the sum of all the individual pressures
2 more items...
An ideal gas follows these and the gas laws perfectly, meaning there are no other interactions except from the perfectly elastic collisions between gas molecules.
Section 9: Astrophysics :space_invader:
Telescopes
Convex/Converging lens:
Focuses incident light
Concave/Diverging lens:
Spreads out incident light
Principal Axis:
The line passing through the centre of the lens at 90 degrees to the surface
Principal Focus (F):
Converging lens:
The point where incident beams passing parallel to the principal axis will converge
Diverging lens:
The point where light rays appear to come from (same distance either side of the lens)
Focal length (f):
Distance between the centre of the lens and the principal focus (shorter focal length = stronger lens)
Real image:
Form when light rays cross after refraction. Real images can be formed on a screen.
Virtual image:
Formed on the same side of the lens. Light rays don't cross so an image cannot be formed.
Lens formula:
1/u + 1/v = 1/f
Power of a lens (P):
How closely a lens can focus a beam that is parallel to the principal axis (measured in Dioptres)
Refracting telescope: (two lenses)
Made up of two lenses: The objective lens and the eyepiece lens.
Objective lens:
Collects light and creates a real image. Should have a long focal length and be large
Eyepiece lens:
Magnifies the image produced by the objective lens. Produces a virtual image at infinity
Normal adjustment:
Distance between objective lens and eyepiece lens is the sum of their focal lengths. This means the principal focus of the two lenses is in the same place.
Magnifying power (M):
Angle subtended by image at the eye / angle subtended by the object at the unaided eye
Always larger angle over smaller angle
When both angles less than 10 degrees, M = objective lens focal length divided by eyepiece lens focal length
Reflecting Telescopes:
Cassegrain reflecting telescope:
Newtonian reflecting telescope:
Chromatic Aberration
: Focal length of different light rays (e.g. red light and blue light) are different, meaning they are focussed at different points
Caused by refraction, so has very minimal effects on reflecting telescopes
Can cause white objects to have coloured fringing/edges
Spherical Aberration:
The curvature of a lens/mirror can cause rays of light to be focused at different positions, which blurs images
Most visible in large diameter lenses
Can be reduced/ completely avoided using parabolic mirrors
Achromatic Doublet:
A way of minimising spherical and chromatic aberration. Consists of a crown glass convex lens and a flint glass concave lens cemented together
Radio, IR, UV, X-ray and Gamma telescopes:
Radio telescopes:
Atmosphere does not absorb radio waves, allowing them to be built on the earth
Should be built in isolated locations to avoid interference from nearby radio sources
Uses a parabolic primary dish to focus radio waves onto a detector/receiver, to create a digital image.
Infrared Telescopes:
Use IR radiation to produce images of astronomical objects.
Large concave mirrors focusing radiation onto a detector. Needs to be cooled to almost absolute zero and be shielded to avoid thermal contamination
Used to observe cooler regions in space. Atmosphere absorbs most IR radiation so IR telescopes must be in space
Ultraviolet Telescopes:
Use UV radiation to create images of astronomical objects
Ozone layer blocks all UV rays of wavelength less than 300nm, so UV telescopes must be positioned in space
Uses the cassegrain configuration to focus UV rays onto a Solid State Device (Uses photoelectric effect to convert photons to electrons, which then travel around a circuit)
X-Ray Telescopes:
Use X-rays to create images of astronomical objects, usually high energy events such as black holes or neutron stars
All X-rays are absorbed by the atmosphere, so X-ray telescopes must be in space
Must be made from a combination of parabolic and hyperbolic mirrors that are extremely smooth, to focus X-rays onto CCDs that convert light into an electrical pulse
Charge-coupled devices (CCDs):
An array of light sensitive pixels, which become charged when they are exposed to light by the photoelectric effect
More useful for detecting finer details and producing images that can be shared and stored
Gamma Telescopes:
Do not use mirrors as gamma radiation has high enough energy to pass straight through. Use a detector made of layers of pixels.
As photons pass through, they cause a signal in each pixel they come into contact with
Used to detect gamma ray bursts (GRBs), quasars, black holes, and solar flares
Short-lived GRB: lasts between 0.01-1 second
Thought to be black hole formations, or a neutron star falling into a black hole
Long-Lived GRB: lasts between 10-1000 seconds
Associated with a type 2 supernova
Collecting power:
A measure of the ability of a lens/mirror to collect incident EM radiation.
Collecting power is directly proportional to the area of the objective lens
Collecting power ∝ objective diameter squared
Resolving Power:
The ability of a telescope to produce separate images of close together objects
θ = λ/D
θ = min angular resolution
λ = wavelength of radiation
D = diameter of objective lens/mirror
AKA the Rayleigh criterion: Two objects will not be resolved if any part of the central maximum of the images falls within the central white spot of the diffraction pattern
Classification of Stars
Classification by Luminosity
Luminosity:
rate of light energy released/power output of a star
Intensity:
Power received (luminosity) from a star per unit area. Follows the inverse square law
Apparent magnitude (m):
How bright the object appears from the earths surface.
Hipparcos scale classifies objects via their apparent magnitudes, from m = 1 (brightest) to m = 6 (dimmest). Intensity of a magnitude 1 star is 100x greater than a magnitude 6 star. It is logarithmic (ratio of 2.51)
A lower apparent magnitude usually indicates a brighter star
Absolute magnitude (M):
The apparent magnitude when viewed from a distance of 10 parsecs
m - M = 5log(d/10)
m = apparent magnitude
M = absolute magnitude
d = distance in parsecs
Parallax:
The apparent change of position of an object in comparison to a background of further away objects, as a result of the earths orbit around the sun.
Units of distance:
Astronomical unit (AU):
The average distance between the centre of the earth and the centre of the sun (radius of the earths orbit around the sun)
Parsec (pc):
The distance at which the angle of parallax is 1 arcsecond (1/3600 degrees)
Light year (ly):
The distance that an EM wave travels in a year in a vacuum
Classification by temperature & Black-body radiation:
A black-body radiator is a perfect emitter and absorber of all wavelength of radiation
Stefan's law: P = σAT^4
P = Power/Luminosity
σ = Stefan constant (5.67x10-8 W m-2 K-4)
A = Surface area
T = Absolute temperature (K)
Wien's displacement law: λT = 0.0029 mK
(metre-Kelvin)
Shows that peak wavelength of a black body decreases with temperature, meaning frequency increases so the energy of the wave increases.
I = P/4πd^2
I = Intensity
P = Power output
d = distance from star
Stellar spectral classes:
Stars can be classified into spectral classes based on the strength of absorption lines
Class B:
Blue, 11000-25000K, (He, H), Slightly stronger H balmer lines
Class A:
Blue/White, 7500-11000K, (H, Ionised metals), Strongest H balmer lines
Class F:
White, 6000-7500K, (Ionised metals), Weak H balmer lines
Class O:
Blue, 25000-50000K, (He+, He, H), Weak H balmer lines
Class G:
Yellow/White, 5000-6000K, (Ionised/neutral metals), No H balmer lines
Class K:
Orange, 3500-5000K, (Neutral metals), No H balmer lines
Class M:
Red, <3500K, (Neutral atoms, Titanium Oxide), No H balmer lines
Colour, Temperature, Prominent absorption lines, Prominence of H balmer lines
Hydrogen balmer lines are absorption lines that are found in O, B and A
Caused by excitation of hydrogen atoms from the n=2 state to higher/lower energy levels
The Hertzsprung Russel (HR) diagram:
A logarithmic graph plotting absolute magnitude against temperature
Our sun's evolution: protostar - main sequence - red giant - white dwarf.
Supernovae, Neutron stars, and black holes:
1 sol (solar mass)
= 1x10^30 kg
Stages of stellar evolution:
Nebula:
Clouds of gas/dust
Protostar:
Nebula clumps together under gravity and begin to rotate, forming a dense core (the protostar). When it gets hot enough it begins to fuse.
Main Sequence:
Inward force of gravity and outward force of fusion (radiation pressure) are in equilibrium. Star is stable. H fused into He. Greater mass = shorter main sequence period (fuses quicker)
Red Supergiant (For stars >3 sol):
When a high-mass star runs out of H nuclei, same process for a red giant occurs but on a much larger scale. Can fuse elements up to iron.
Red Giant (For stars <3 sol):
Once hydrogen runs out, core temperature increases and He nuclei begin fusing into heavier elements. Outer layers of the star expand and cool.
White dwarf (For stars <1.4 sol):
When a red giant has used up all fuel, fusion stops and the core collapses as gravity is now greater than the outward radiation pressure. Outer layers are thrown off, and the core becomes very dense.
1 more item...
Supernova (For stars > 1.4 sol):
When all fuel runs out, fusion stops and the core collapses inwards suddenly and becomes rigid. Outer layers of the star collapse in and rebound off the core, sending it into space in a shockwave. Causes elements heavier than iron to be fused, and remaining core depends on the mass of the star.
2 more items...
Schwarzschild radius:
radius of the event horizon of a black hole.
Rs = 2GM/c^2
Rs = Schwarzschild radius
G = Gravitational constant
M = Mass of black hole
c = Speed of light
Binary system:
Where two stars orbit a common mass
Types of Supernovae:
Type 1:
When a star accumulates matter from its companion star and explodes after reaching a critical mass. Show no strong H lines and are further subdivided into 3 groups.
Type 1a:
Type 1 supernova of a white dwarf. Rapidly reach peak luminosity (~109x the sun) then decrease gradually. Show strong silicone absorption lines.
Type 1b:
Type 2 supernova of a red supergiant. Similar properties to 1a, but show strong He lines instead of silicone
Type 1c:
Type 2 supernova of a red supergiant. Similar properties again, but shows no strong absorption lines
Type 2:
The collapse and explosion of a red supergiant. Have strong H and He lines. Peak luminosity not as high as a type 1a, and light output decreases gradually but unsteadily.
Hubble's law:
Shows that the universe is expanding. Suggested objects should appear brighter than expected, however type 1a supernovae appear dimmer, which suggests the expansion of the universe is accelerating
Dark Energy:
Thought to be the reason behind the universes expansion. Said to have an 'overall repulsive effect throughout the whole universe'.
Remains constant throughout the universe, meaning it has a greater effect than gravity and causes expansion to increase
Controversial because there is evidence for its existence, but no one knows what it is or what it is caused by.
WAVES 🌊
PROGRESSIVE WAVES
Amplitude - A waves maximum displacement from equilibrium
Frequency - The number of complete oscillations passing through a point per second.
Wavelength - The length of one whole oscillation
Phase - The position of a certain point on the wave cycle
Phase difference - How much a particle / wave lags behind another particle / wave
Period - Time taken for one complete oscillation
Two points on a wave are in phase if they are both at the same point of the wave cycle. They will have the same displacement and velocity.
Two points on a wave are completely out of wave when they are half cycles apart
LONGITUDINAL AND TRANSVERSE WAVES
Transverse - oscillation of particles is at right angles to the direction of energy transfer E.G. EM WAVES
Longitudinal - oscillation of particles are parallel to the direction of energy transfer E.G. SOUND WAVES
Longitudinal waves are made up of compressions are rarefactions
Polarised waves - a polarised wave can only oscillate in one plane, only transverse waves can be polarised
Polaroid sunglasses are an example of polarisation, they reduce glare by blocking partially polarised light reflected from objects. Other examples: Tv and radio signals
PRINCIPLE OF SUPERPOSITION OF WAVES AND FORMATION OF STATIONARY WAVES
Superposition - where the displacements of two waves are combined as they pass each other, the resultant displacement is the vector sum of each waves displacement
Constructive interference - when two waves have displacement in the same direction
Destructive interference - when one wave has positive displacement and the other has negative.
A stationary wave is formed from the superposition of two progressive waves, travelling in opposite directions in the same plane, same frequency wavelength and amplitude
No energy is transferred in a stationary wave
When they meet in phase, constructive interference occurs
Antinodes are formed which are regions of maximum amplitude
When they meet completely out of phase destructive interference occurs
nodes are formed which are regions of no displacement
REFRACTION, DIFFRACTION AND INTERFERENCE
Path difference - the difference in distance travelled by two waves
A coherent light source - the same frequency and wavelength and a fixed phase difference
Young’s Double slit experiment
demonstrates interference of light from two sources
Shine a coherent light source through 2 slits about the same size as the wavelength of the laser light so the light diffracts
Each slit acts as a coherent point source making a pattern of light and dark fringes. Light fringes are formed where the light meets in phase and interferes constructively, this occurs where the path difference between waves is a whole number of wavelengths (nA, where n is an integer).
Dark fringes are formed where the light meets completely out of phase and interferes destructively, this occurs where the path difference is a whole number and a half wavelengths ((n+½)Л).
W is fringe spacing
Lamda is wavelength
D is distance between screen and splits
s is slit separation
Evidence of the wave nature of light is provided with Young’s double slit experiment because diffraction and interference are wave properties
DIFFRACTION
Diffraction is the spreading out of waves when they pass through or around a gap
The greatest diffraction occurs when the gap is the same size as the wavelength
Monochromatic light can be diffracted through a single slit onto a screen, which forms an interference pattern of light and dark fringes
White light is made up of all colours, therefore all different wavelengths of visible light.
The diffraction pattern is a central white maximum with alternating bright fringes which are spectra
In order to vary the width of the central maximum, you can vary slit width and wavelength.
increasing the slit width decreases the amount of diffraction and therefore narrows the central maximum but the intensity increases
increasing the wavelength increases the amount of diffraction, therefore the central maximum becomes wider and the intensity decreases
A diffraction grating is a slide with equally spaced slits very close together
This produces a much more sharp and bright interference pattern as there are many more rays of light reinforcing the pattern.
The ray of light passing through the central slit is called the zero order line and the slits each side of this one are called the first order lines and so on.
dsinx = n x wavelength
REFRACTION AT A PLANE SURFACE
A refractive index (n) is a property of a material which measures how much it slows down light passing through it
n = c/cs
a material with a higher refractive index can also be known as being more optically dense
refraction occurs when light enters a new medium, causing it to change in direction
When n2 is more optically dense than n1, the ray of light slows down and bends TOWARDS the normal
As the angle of incidence increases , refraction also increases until it reaches the critical angle at 90 degrees.
TIR can occur when the angle of incidence is greater than the critical angle and n1>n2
A useful application of TIR is optical fibres. They have an optically dense core surrounded by cladding with a lower optical density, allowing TIR to occur
Signal degradation:
Absorption - where part of the signals energy is absorbed by the fibre, reducing amplitude of the signal
Dispersion - This causes pulse broadening
Modal - caused by light rays entering the fibres at different angles, therefore they take different paths along the fibre
1 more item...
Section 7: Fields and their consequences
:gear:
Gravitational fields :earth_africa:
Newtons laws
Gravity
acts on any object with mass. It is always attractive.
Newton's law of gravitation
shows that the magnitude of the gravitational force between two masses is directly proportional to the product of the the masses, and is inversely proportional to the square of the distance between them.
G
is the
Gravitational constant
and is equal to 6.67 x10^-11
Gravitational field strength
A gravitational field can be a
uniform field
or a
radial field
The arrows on the field lines show the direction that the force acts
A uniform Field exerts the
same
gravitational force everywhere in the feild
Demonstrated by parallel equally spaced lines
In a radial field the force exerted depends on the position of the object
::Gravitational field strength(g):: is the force per unit mass exerted by a gravitational field
Gravitational Potential(V)
The work done per unit mass against gravitational force to move an object from infinity to a given point
At infinity V is zero, as object moves from infinity to a point, energy is released as the GPE is reduced therefore V is negative
V= - GM/r
Gravitational Potential difference(ΔV) is the energy needed to move a unit mass between two points
Work done = mΔV
Equipotential surfaces
are surfaces created joining points of equal potential together, on an equipotential surface V is constant
Is
zero
work done to move along an equipotential
If plot Potential against distance the gradient of the tangent to a point is equal to -g
If plot g against r the ΔV is equal to the area under the graph
Orbits of planets and satellites
Kepler's third law
is that the square of the orbital period(T) is directly proportional to the cube of the radius(r)
Object in orbit experiences gravitational force towards the centre. This force is acting as a centripetal force. Can equate the two equations
Rearrange the equation to make v² the subject
As velocity is the rate of change of displacement can find v in terms of r and T, square it to get an equation for v²
Substitute the equation for v² in terms of r and T. Then just rearrange to make T² the subject.
The total energy of a satellite is the sum of its kinetic energy and of its potential energy. This is kept constant while in orbit.
The
escape velocity
of an object is the minimum velocity it must travel to escape the gravitational field at the surface. Is point where Ep = Ek
escape velocity is independent of mass of the object
A
synchronous orbit
is one which has a orbital period equal to the rotational period of the object it is orbiting. On earth would have a period of 24 hours
A
Geostationary satellites
have a period of 24 hours and stays above the same point on the equator
Used for sending Tv and telephone signals
Low orbit satellites
are very low but travel alot faster due to small orbital period. Useful for monitoring weather, observations and military applications
Section 5: Electricity :zap:
Basics of electricity
Current (I):
The flow of charge per unit time/ The rate of flow of charge.
I = Q/t
I = Current (A)
Q = Charge (C)
t = Time (s)
Potential Difference (V):
The energy transferred per unit charge between two points in a circuit.
V = W/Q
V = Potential Difference (V)
W = Energy transferred (J)
Q = Charge (C)
Resistance (R):
A measure of how difficult it is for charge to pass through a component
R = V/I
R = Resistance (Ω)
V = P.D (V)
I = Current (A)
Current-Voltage Characteristics:
Ohms law:
For an ohmic conductor, current is directly proportional to the P.D across it (In constant conditions)
Ohmic Conductor:
A component that follows ohms law. Has a straight line through the origin current voltage graph
Semiconductor Diode:
A component that has forward and reverse bias which can affect the current flow.
Filament Lamp: Obeys ohms law at low currents, but as current increases the graph begins to curve
unless the question states otherwise, ammeters are assumed to have 0 resistance, and voltmeters are assumed to have infinite resistance.
Resistivity:
Resistivity (ρ):
A measure of how well a material conducts electricity
ρ = RA/L
ρ = Resistivity (Ω⋅m)
R = Resistance (Ω)
A = Area (m^2)
L = Length (m)
When the temperature of a metal conductor increases, its resistance also increases.
Thermistors:
As the temperature increases, resistance decreases.
Superconductors:
A material which has zero resistivity below its critical temperature.
Circuits:
Series Circuits:
Resistance in series:
R = R1 + R2 + R3 + ...
Current is the same everywhere
Battery P.D shared across all elements (sum of V across all elements == Supply P.D
Parallel circuits:
Resistance in Parallel:
1/R = 1/R1 + 1/R2 + 1/R3 + ...
Sum of currents in each parallel set of branches is equal to total current.
P.D across each branch is the same.
Power (P):
The energy transferred per unit time.
P = VI = V²/R = I²R
Cells:
Identical cells joined in parallel:
V = V1 = V2 = V3 = ...
Joined in series:
V = V1 + V2 + V3 + ...
DC circuits:
Charge and energy are always conserved (Kirchhoff's laws)
Kirchhoff's 1st Law: Total current flowing into a junction is equal to the current flowing out of that junction.
Kirchhoff's 2nd Law: Sum of all the voltages in a series circuit is equal to the battery voltage.
Potential Dividers:
A circuit with several resistors in series connected across a voltage source, used to produce a required fraction of the source P.D (which remains constant)
Using a variable resistor will make the potential divider supply a variable P.D
Light Dependent Resistor (LDR):
Resistance decreases as light intensity increases.
EMF and Internal Resistance:
Batteries have an internal resistance (r) caused by electrons colliding with atoms inside the battery
Electromotive force (emf / ε):
Energy transferred by a cell per coulomb of charge
ε = E/Q
ε = emf (V)
E = energy (J)
Q = charge (C)
Total resistance = sum of internal resistance (r) and resistor resistance (R)
ε = IR + Ir
ε = I(R + r)
P.D across resistor R = Terminal P.D
P.D across cell (internal resistance r) = Lost volts (v)
Lost volts = energy wasted by the cell per coulomb of charge
V = IR
so
v = Ir
, and therefore emf is the sum of the terminal P.D and lost volts
(ε = V + v)
Section 2: Particles and Radiation :radio:
Particles:
Constituents of the atom:
Protons:
Charge (C):
+1.6x10^-19 C
Relative C:
+1
Mass:
1.67x10^-27 kg
Relative M:
1
Specific C:
9.58x10^7 C/kg
Neutrons:
Charge (C):
0 C
Relative C:
0
Mass:
1.67x10^-27 kg
Relative M:
1
Specific C:
0 C/kg
Electrons:
Charge (C):
-1.6x10^-19 C
Relative C:
-1
Mass:
9.11x10^-31 kg
Relative M:
0.0005
Specific C:
1.76x10^11
Specific Charge:
The charge-mass ratio of a particle. Specific charge = Charge/Mass
Isotopes:
An atom that has the same number of protons but a different number of neutrons.
Stable and Unstable Nuclei:
Strong Nuclear Force (SNF):
Keeps nuclei stable by counteracting the electrostatic force of repulsion between protons and neutrons. Attractive up to 3 fm, repulsive below 0.5 fm.
Unstable nuclei:
Nuclei which have either too many protons, neutrons or both. Causes the SNF to not be enough to keep them stable.
Beta- Decay:
Occurs in neutron-rich nuclei. Is an electron and anti-electron neutrino
Beta+ Decay:
Occurs in proton-rich nuclei. Is a positron and electron neutrino
Alpha Decay:
Occurs in large nuclei. It is a Helium nucleus (2 protons, 2 neutrons)
Particles, Antiparticles and photons:
Each particle has a corresponding antiparticle which has the same rest energy and mass, but all other properties are opposite.
Photons:
Packets of EM radiation. Transfer energy and have no mass.
E = hf = hc/λ
Annihilation:
A particle and its antiparticle collide, converting their masses into energy. Releases 2 photons of equal energy in opposite directions
Pair Production:
A photon is converted into a particle-antiparticle pair, with any excess energy converted to kinetic energy of the particles.
Particle Interactions:
Strong Nuclear:
Gluon, 3x10^-15m, Hadrons
Weak Nuclear:
W+/W- boson, 10^-18m, All particles
Electromagnetic:
Virtual Photon, Infinite, Charged Particles
Gravity:
Graviton, Infinite, Particles with Mass
Name: Exchange particle, Range, Acts on
Feynman diagrams:
Electron capture:
Beta-Plus decay:
Electron-Proton collision:
Beta-Minus decay:
Classification of Particles:
Hadrons
Not fundamental, experience the strong nuclear force
Formed from quarks (quarks are fundamental)
Further separated into:
Anti-Baryons:
3 antiquarks (e.g: antiproton, antineutron)
Mesons:
Quark - Antiquark (e.g: Pion up-antidown, Kaon up-antistrange)
Baryons:
3 quarks (e.g: Proton uud, Neutron udd)
Leptons:
Fundamental particles (Cannot be broken down any further)
Don't experience the strong nuclear force
e.g: Electron, Muon, Electron neutrino, Muon neutrino, (+ their antiparticles)
In particle interactions:
Baryon number is always conserved (Is always a whole number)
Proton is the only stable baryon
Lepton number is always conserved (Both muon and electron lepton number) (Always a whole number)
Muons decay into electrons
Strangeness is only conserved in the strong interaction (Can change in the weak interaction)
Scientific investigations rely on collaboration of scientists internationally
Quarks and antiquarks:
3 quark types:
(Charge, Baryon number, Strangeness)
Up:
+2/3 e, +1/3, 0
Down:
-1/3 e, +1/3, 0
Strange:
-1/3 e, +1/3, -1
Applications of conservation laws:
Always conserved in particle interactions:
Energy
Momentum
Baryon number
Muon and electron lepton numbers
beta- and beta+ are both caused by the weak interaction
EM radiation and quantum phenomena:
The photoelectric effect:
Electrons are emitted from the surface of a metal after light above a certain frequency is incident on it.
This certain frequency is called the threshold frequency (It is different for different metals)
Threshold frequency couldn't be explained by wave theory, but can be explained by the photon model of light
EM waves travel in 'discrete packets' called photons
Each electron absorbs one photon, so an electron is only emitted if the frequency is above the threshold frequency
Work function (Φ):
The minimum energy required for electrons to be emitted from the surface of a metal.
Stopping potential (Vs):
The P.D. needed to be applied across the metal to stop electrons with maximum kinetic energy
Ek(max) = e x Vs
E = hf = hc/λ = Φ + Ek(max)
Collisions of electrons with atoms:
Electrons can only exist in discrete energy levels inside an atom
Excitation: When an electron moves up energy levels
occur when an electron gains energy from a collision with a free electron
If an electron becomes excited, it will quickly return to its original energy level and release the energy it gained as a photon
Ionisation: When an electron is removed from the atom entirely
occur if the energy of the free electron is greater than the ionisation energy
Fluorescent tubes:
Filled with mercury vapour, and a high voltage is applied across
Voltage accelerates free electrons through the tube causing them to collide with the mercury atoms & ionising them.
The free electrons then excite the mercury atoms, and when they de-excite they release photons in the UV range
The phosphorous (fluorescent) coating on the inside of the tube absorbs the UV photons which excites and de-excites the phosphor atoms which then release photons of visible light.
Electron Volt: The energy gained by one electron when passing through a P.D of 1V
1 eV = 1.6x10^-19 J
Energy levels & photon emission:
Passing light from a fluorescent tube through a diffraction grating/prism gives a line spectrum
Each line represents a different wavelength of light emitted.
Not continuous, only contains discrete values of wavelength so only photon energies emitted will correspond to these wavelengths
Evidence to show electrons in atoms can only transition between discrete energy levels
Passing white light through a cooled gas gives an absorption spectrum
Black lines represent the absorbed wavelengths
Difference between two energy levels is equal to a specific photon energy emitted
ΔE = E1 - E2
as E = hf, hf = E1 - E2
Wave-Particle duality:
Light can be shown to have both wave and particle properties
Wave e.g: diffraction and interference
Particle: Photoelectric effect
Electrons can be shown as having both wave and particle properties
Wave nature is observed through electron diffraction
De Broglie suggested that if light has particle properties, particles should have light properties
λ = h/mv
Knowledge and understanding of scientific concepts change over time in accordance to the experimental evidence gathered
Evidence must first be peer reviewed by the community to become validated and accepted.
NUCLEAR PHYSICS
Rutherford scattering
Rutherford scattering demonstrated the existence of a nucleus
Before this, scientists believed that the atom was made of a sphere of positive charge with small areas of negative charge evenly distributed around
Rutherford's apparatus included an alpha source and gold foil in an evacuated chamber which was covered in fluorescent coating.
Most alpha particles passed straight through the foil with no deflection which suggests most of the atom was empty sapce
A small amount of particles were deflected at a large angle which suggests the centre of the atom is positively charged
very few particles were deflected more than 90 degrees which suggests that the centre of the atom was very dense.
Alpha, Beta and Gamma radiation
Radiation is where an unstable nucleus emits energy in the form of EM waves or subatomic particles in order to become more stable
ALPHA
2-10cm range in air
Highly ionising
Deflected by electric and magnetic fields
Absorbed by paper
BETA
1m range in air
Weak ionisation
Deflected by electric and magnetic fields
absorbed by around 3mm aluminium foil
GAMMA
Infinite range in air
very weak ionisation
Not deflected by electric and magnetic fields.
Absorbed by several metres of concrete or several inches of lead
All three types of radiation can be used to test material thickness
For example, beta radiation can be fired at aluminium foil with a detector placed on the other side. If the material becomes too thick, less beta radiation will be picked up from the other side.
Gamma radiation can be used in medicine as a detector, to sterilise surgical equipment, and in radiation therapy
As gamma radiation moves in the air it spreads out equally in all directions
Radioactive sources must be handled safely by:
using long handled tongs to move sources
storing the source in a lead lined container
Keeping the source as far away from you and others
Never pointing the source towards others
Background radiation is present everywhere so it is important to measure the amount of background radiation before an experiment.
Sources of background radiation:
Radon gas - which is released from rocks
Artificial sources - nuclear weapon testing and nuclear meltdowns
Cosmic rays - enter the earths atmosphere from space
Rocks containing naturally occurring radioactive isotopes
Radioactive decay
Radioactive decay is a random process meaning you can't predict when the next decay will happen
A given radioactive nucleus will have a constant decay probability known as the decay constant
As the decay is exponential, the time taken for the number of nuclei to halve will be constant, the
name for this value is the half-life (T1/2) of the sample
The activity of a radioactive sample is the number of nuclei that decay per second, this is proportional to the number of nuclei in the sample.
The decay constant can be used to model the decay of a nuclei only when there is a large number of nuclei in the sample, this is because the decay constant models the number of nuclei decayed by statistical means.
Section 4: Mechanics & Materials :male-mechanic:
Force, Energy & Momentum:
Scalars and Vectors:
Scalar:
Only magnitude
Vector:
Direction & magnitude
To add vectors, use Pythagoras or trigonometry, or draw a scale diagram
To resolve vectors, use trigonometry
Equilibrium:
Sum of all forces acting on a point are equal to 0
No resultant force = object will be stationary or moving at a constant velocity
Moments:
The moment of a force about a point is the force x perpendicular distance to the pivot
M = F x d
A couple is a pair of coplanar forces, where the two forces are equal in magnitude but act in opposite directions
Moment of a couple:
multiply one of the forces by the perpendicular distance between the two forces
Principle of moments:
For an object to be in equilibrium, the sum of anticlockwise moments is equal to the sum of clockwise moments.
Centre of mass:
The point at which an objects mass acts. (A uniform object has its centre of mass exactly at the centre)
Motion along a straight line:
Speed:
scalar quantity which describes how quickly an object is travelling
Displacement (s):
The overall distance travelled from the starting position
Velocity (v):
Rate of change of displacement
Acceleration (a):
Rate of change of velocity
Acceleration-time graphs represent the change in acceleration over time
Area under graph = velocity
Velocity-time graphs represent the change in velocity over time
Gradient = velocity
Area under graph = displacement
Gradient of a displacement-time graph shows velocity
Use SUVAT formulae for uniform acceleration
Projectile motion:
Vertical and horizontal components of motion are independent
Free fall:
Object experiences acceleration of g (9.81 m/s)
Friction:
A force that opposes the motion of an object
Frictional forces convert kinetic energy into other forms e.g. heat or sound
Lift:
Upward force that acts on an object travelling through a fluid (e.g. water, air)
Terminal speed:
Frictional forces and driving forces are balanced, so acceleration is 0 and the object travels at constant velocity
Air resistance affects both vertical and horizontal components of a projectiles motion
