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A-Level Physics Paper One - Coggle Diagram
A-Level Physics Paper One
HFS
v = u + at
v^2 = u^2 + 2as
s = ut + (1/2)at^2
s = vt - (1/2)at^2
s = (v+u / 2)t
CPAC 1
Methods (both have external timer and electromagnet):
Light gates (use dowel, measuring the length of the dowel and taking this to be s).
Trap door.
When we have two springs in series: 1/k[total] = 1/k[1] + 1/k[2] ...
SPC / DIG
At any instant, the resistance across a component can be calculated by the ratio of the p.d. to the current.
An Ohmic device displays a directly proportional relationship between the p.d. and current flow (resistance is constant) provided that the temperature is constant.
The total current flowing into a junction is equal to the total current flowing out of the junction due to conservation of charge.
The distribution of potential differences around a circuit is explained using conservation of energy. This outlines that the sum of potential differences in a closed loop is zero.
A semi-conductor diode works by only allowing current to flow when a threshold voltage is surpassed.
The IV graph for a NTC thermistor can be figured out by appreciating that as current increases, the component heats up and resistance decreases.
Resistivity is a measure of how easily a material conducts electricity. It is given by rho = RA / L.
The current flowing through a wire depends on:
The number of charged particles travelling across it (charge carrier density [number of charged particles per unit volume]).
The speed at which the charged particles are travelling. The average speed is called the drift velocity.
The charge possessed by a single charged particle.
The potential along a uniform wire increases uniformly with the distance along it.
We can replace a resistor in a potential divider circuit with an LDR or thermistor to form a light or temperature sensor.
LDR: As light intensity increases, resistance decreases and so current increases. As a result, the potential across the second component increases.
The internal resistance of a battery is caused by electrons colliding with atoms inside of the battery. The electromotive force of a battery is the number of joules supplied to each coulomb of charge passing through it. It is equal to the product of the current and the total resistance of the circuit.
The lost volts are the product of the current in the circuit and the internal resistance of the battery. It is the difference between the theoretical p.d. (EMF) and terminal p.d.
When the circuit is open (the current through the battery is 0), the EMF is the voltage over the battery.
Atoms in most solids are arranged in a crystal lattice structure. As temperature increases, the intensity of vibration (about the equilibrium position) of these atoms increases. The more intense the lattice vibrations, the more difficult it is for free electrons to pass through the material (electrons are more likely to collide). This causes resistance to increase.
As the temperature of a metal or semiconductor increases, thermionic emission is allowed. For semi-conductors, resistance decreases (as the charge carrier density increases). For metals, resistance still increases (the effects of thermionic emission do not outweigh the effects of lattice vibrations).
LDRs are made from photoconductive materials. And so as light intensity increase, the charge carrier density increases and so the resistance decreases.
CPAC 3
Use equation V = -Ir + Epsilon. Vary the current in the circuit and measure the potential difference across the fixed resistor.
TRA
CPAC 9
Ramp should be tilted to counter-act friction.
Keep the mass of the system the same by transferring mass from the trolley to the hanger.
Add mass onto hanger to provide a force of mg.
Use a data logger to record the speed of the trolley as it passes through two light gates and the time taken to move between these gates.
Calculate the change in velocity.
Use the relation mt = (v2 - v1)(M / g) to determine g or M (using the gradient).
An elastic collision is a one where both momentum and kinetic energy are conserved. A inelastic collision is a one in which momentum is conserved but kinetic energy is lost and transferred to another energy store. If two objects stick together after a collision then it is inelastic.
Capacitance is the charge stored by a capacitor per unit of potential difference. The electrical energy stored by a capacitor is given by the area under a charge against potential difference graph (W = 0.5 x QV or W = 0.5 x CV^2)
Once a capacitor is connected to a power supply, current starts to flow and negative charge builds up on the plate connected to the negative terminal. This build up of negative charge pushes electrons away from the other plate, causing it to become positively charged. This creates an increasing potential difference and increasing charge but decreasing current (due to electrostatic repulsion).
When a capacitor is discharging, current, charge and potential difference all fall exponentially. This is because of a decreasing electrostatic repulsion.
The product of the resistance and the capacitance is known as the time constant. This is the time taken to discharge a capacitor to 1/e of its initial value to charge one to (1 - 1/e) of its initial value.
The magnetic flux density of a magnetic field is a measure of the strength of the field. It is measured in Teslas.
Magnetic flux describes the magnetic field lines passing through a given area. It is given by the product of the magnetic flux density, the area and the sin of the angle.
Magnetic flux linkage is the product of the magnetic flux and the number of turns in the coil.
The force exerted on a charged particle moving in a magnetic field is F = BQvsin(theta). Theta here is the angle between the velocity of the particle and the magnetic field.
To find the direction of the force exerted on an electron (conventional current), Fleming's left hand rule can be used. Right hand can be used for positively charged particles.
The force exerted is always perpendicular to the direction of motion. This causes the motion of a charged particle in a magnetic field to be circular (force acts as a centripetal force).
When a conducting rod moved through a magnetic field, the electrons within will experience a force and build up on one side of the rod. This causes an EMF to be induced within the rod. This is known as electromagnetic induction.
Faraday's Law states that the magnitude of the induced EMF is equal to the rate of change of flux linkage. Lenz's Law states that the direction of induced current is opposes to the motion causing it.
If a coil of wire experiences a changing current, a changing magnetic field will be formed. If a second coil is within this magnetic field then will have an EMF induced upon it. This principle is called mutual inductance.
Lenz's law is a direct consequence of the conservation of energy: it ensures that the electrical energy gained by an induced current is offset by the energy lost by the system (removal of kinetic energy).
Properties of an alternating PD:
Peak value (maximum amplitude).
RMS (an average of all the squares of the possible values) (this gives the effective output).
Time period.
MDM
An electric field is a region in which a charged object experiences a force. In general, a force field is an area in which an object experiences a non-contact force.
The distance between field lines describes the strength of the field at that point.
Electric field strength is defined at the force experienced coulomb of charge. This value is constant everywhere in a uniform field but varies within a radial field.
Coulomb's Law states that the magnitude of the force experienced between two point charges is directly proportional to the product of their charges and is inversely proportional to the square of the distance between them.
Point charges form a radial field, the field strength of such a field is given by Q / 4 pi epsilon-naught r^2
The absolute electric potential at a point is the potential energy per unit charge of a positive point charge. It is the energy required (per unit charge) to move a charge to a specific point within the field.
We can calculate the electric field between two parallel plates with E = V / d.
Electric potential difference is the energy needed to move a charge between two points.
Field lines for an electric field show the direction in which a positive charge would move when in the field. The potential on an equipotential surface is equal everywhere. No work is done when a charge move along a line of equipotential. These are parallel line (perpendicular to the plates) for a uniform field and concentric circles for point charges.
Thermionic emission is where the free electrons on the surface of a metal are heated and released. Electrons can be accelerated using electric fields or accelerated radially using magnetic fields.
An electron gun uses a potential difference to accelerate particles. Electrons are accelerated towards the anode (a NOD = positive).
PRO
Angular displacement is the angle moved through by an object. Angular velocity is the angle an object moves through per unit time. This can be calculated by dividing the object's linear velocity by the radius.
Angular velocity = 2pi / T
In order to derive an equation for angular acceleration:
Draw a circle with an object moving through an angle of delta(theta) over a an arc of length delta(s).
Determine that the angle between the initial and final velocity vectors is theta also. Use similarity rules to determine that delta(v) / v = delta(s) / r
An object moving in a circle at a constant speed still has a changing velocity and therefore an acceleration. Due to Newton's first law, this means that the object experiences a resultant force. This centripetal force acts towards the centre of the circle. This force is always required to produce and maintain circular motion.
A nucleon (mass) number is the total number of neutrons and protons within an atom (above element). The proton (atomic) number is the number of protons in an atom (below element).
LINACS: Use alternating electric field. Uses several cylindrical electrodes (called drift tubes) that increase in length (adjacent tube have opposite charge). An AC supply is supplied to each of the electrodes. The particles are attracted to the midpoint of a tube and then the AC supply switches direction. The length of each tube is calculated so that the polarity of the voltage across the tube switches when the particle exits. The tubes are successively longer because the particles must be under acceleration for the same amount of time per tube.
Cyclotron: Constructed from two semi-circular "dees". A particle is initially fired from the centre of the cyclotron into one of the electrodes. The magnetic field in the electrodes is perpendicular to the direction of motion so they trace a semi-circular path. The p.d. between the electrodes accelerates the particle between the gaps. The particle then follows a larger semi-circular path in the next dee. The p.d. is switched so that the particle accelerates towards the other dee.
A charged particle that is present in a magnetic field with motion perpendicular to the direction of that field experiences a (centripetal) force that is perpendicular to its velocity.
Because the radius of a particle within a dee is proportional to its velocity, the time spent in each dee is always the same. This allows for an AC supply of a constant frequency to be used.
Rutherford scattering: Alpha particles (helium nuclei [+ charge]) fired at gold foil. Microscope moves around to observe florescent screen. Most passes straight through, some where deflected at a large angle and few were reflected back.
For a mass spectrometer, we use an electron gun to fire high energy electrons at a vapour. The electrons collide with molecules within the vapour and cause them to become ionised.
They are then accelerated by an electric field; and enter a region in which a magnetic field acts. Each charge experiences forces in opposite directions.
Only particles that experience equal force will travel in a straight line. They then enter a separation chamber in which a uniform field acts.
By measuring the radius of the particles' paths, we can determine their charge-mass ratios.
The movement of charged particles can be identified through the trails they leave in a cloud chamber. These trails can be identified as charged particles ionise particles in their path.
We can use the radius of a particle's tracks to calculate many of its properties such as its momentum. By finding the direction of curvature, we can find whether the particle is positively or negatively charged. If tracks suddenly stop or change direction then we have a particle collision. If the tracks have seemingly come from nothing then we must be observing an uncharged particle forming a charged particle.
High energies are required to investigate nucleons because they are very small in size. This will require particles (or light) with a very high wavelength to observe the nucleons.
At any time, mass and energy can be exchanged. This can be seen in pair production: this is where a photon is converted to a matter/anti-matter pair. This can only occur because the photon has more energy than the rest energy of the two particles. It can also be seen in annihilation: this is where matter and anti-matter are converted to kinetic energy and photons (moving in opposite directions).
When particles are travelling at speeds that are comparable to the speed of light. They experience time dilation. This effectively means that time runs at different speeds depending on the observer. The lifetime of a particle travelling at relativistic speeds would be longer. Muon decay provides evidence for this. Muons are detected closer to the Earth's surface than they should be: this is because they decay slower from our perspective.
Standard Model
Hadrons:
Formed of quarks.
Experience the strong nuclear force.
Examples include Baryons (3 quarks), anti-baryons (3 anti-quarks) and mesons (quark / anti-quark pair)
Examples of Baryons:
Protons (UUD)
Neutron (UDD)
Examples of Mesons:
Pion (U anti-D) [+ charge]
Kaon (U/D and S) [- charge]
Leptons:
Fundamental particles.
Do not experience strong nuclear.
Examples include: Electrons, neutrinos, muons, tau.