sefp notes
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Notes for SEFP that Ive createdTRANSCRIPT
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relate current and charge for steady and changing currents
For a steady currentQ = It
For a chnaging currentQ = ItI = dQ/dt
explain the meaning of drift velocity and relate it to the current in aconductor
Is the average velocity a charged particle (like an electron)moves through a material.I = nvAq
n = number of charge carries per m^3velocity of carriersA = cross-sectional areaq = charge of each carrier
define potential difference and know how it could be measuredwithout a voltmeter
The p.d. between two points is the electrical energy converted intoother forms of energy when 1 coulomb of charge passes from onepoint to the other
define the e.m.f. and internal resistance of a cell and explain how tomeasure these quantities
The electrical energy produced per unit charge inside the source.
sketch graphs to show the characteristics of different componentsexplain how to measure the resistivity of a material
Chapter 22 | Current and Charge
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carry out circuit calculations for circuits that include resistorcombinations
use Kirchholf's laws to carry out circuit calculations on circuits thatinclude more than one cell
calculate the charge and energy stored in a capacitor and incombinations of capacitors
carry out capacitor charge and discharge calculations
use an ammeter to measure current or a voltmeter to measurepotential difference
carry out calculations to extend the range of a meter
describe and explain the principle of the potential divider
use a potentiometer to compare e.m.fs and to measure small e.m.fs
explain the principle of the Wheatstone bridge and use it to measureresistance and in sensor circuits
carry out appropriate calculations on the Wheatstone bridge
explain thermionic emission and the production of an electron beam
carry out calculations on charged particles in electric and magneticfields
describe a method to measure the specific charge of the electron,e/m describe Millikans method to determine e
outline the significance of the measurement of e/m and of e
describe the principle of the mass spectrometer, the TV tube and the
Chapter 23 | Meters and Bridges
Chapter 27 | Properties of the electron
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oscilloscope
use the photon theory to explain photoelectricity
carry out calculations using Einsteins photoelectric equation
describe the properties of alpha, beta and gamma radiation
describe experiments that demonstrate the properties of alpha, betaand gamma radiation
state the equations for each type of radioactive decay
explain the principle of operation of different detectors of ionizingradiation
describe Rutherford's alpha scattering experiment and how it led tothe nuclear model of the atom
describe methods used to estimate the size of the nucleus
describe the discovery of the neutron
Carry out half-life calculations and describe how to measure half-life
describe and explain ionisation and excitation by collision
Ionisation
Is the process of creating a charged atom by the additionor removal of an electron.To create a negatively charged ion you must give it enoughenergy to escape the pull of the positively charged nucleusThree ways to create ions in the air include:
Allow radioactive particles to pass through the airStriking a match
Chapter 28 | Radioactivity
Chapter 29 | Electrons inside the Atoms
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Using a beam of electrons from an electron gun
The first two methods work by giving energy directly to theelectrons whilst the third works via passing kinetic energy via acollision between two electrons.By adjusting the voltage at the anode; you can change thespeed of the electronA thyratron valve can be used to demonstrate ionisation bycollision.
The valve contains an inert gas like xenon. Increasing theanode voltage gives energy to the electrons however wesee little to no change in the current (as shown below) until12.1V.At 12.1V, electrons have the right amount of kinetic energyto ionise the inert gasThe ion moves towards grid plate which gives us the extracurrent which can be measured
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Excitation
Is the process whereby electrons absorb energy withoutionisationWe can modify the thyratron valve to measure the electronsreaching the anode and we get the following graph:
As we increase the voltage the number of electrons reachingthe anode increases hence the current increases until 8.4vwhere in Xenon the energy is absorbed hence causing the
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current to dropAt this point the electrons are in an excited stateDifferent gasses; absorb energy at different energy levels
relate excitation energies to energy levels and possible photonenergies
When an atom absorbs energy; it's released in the form of ultra-violetradiationYou can find the energy of the emitted photon using it's wavelength:
Energy is absorbed by the atoms in fixed amounts
relate energy level diagrams to possible photon energies
As electrons move down energy levels they release photons ofspecific wavelength/frequency from which we can calculate theirenergy
The hydrogen spectrum follows a specific pattern for it's energylevels. Others don't follow this simple pattern because theelectrons interact with each other.
electrons can travel multiple routes to ground state from an excitedstate. As shown in the diagram below:
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As you can see there are nine possible routes/transitions;therefore there are nine possible wavelengths of energy thatcan be emittedLine emission spectrum is a graph of intensity (photons persecond) against wavelength.
Peaks appear where there are a lot photons being
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released which indicates an energy level
Line absorption spectra is essentially when white light ispassed through a material and different parts of the spectrumget absorbed by the electrons.
We see throughs where there is absorption and thatabsorption indicates an energy level
describe the main features of atomic models that explain energylevels
Bohr developed a model of an atom as a solar system to betterunderstand energy levelsthe electron is in a circular motion around the nucleus where thecentripetal force is provided by the attraction between the nucleusand the electronBohr made a bold assumption of the angular momentum of anelectron being in lumps of h/2piWhen calculating energy released from de-excitement we do:
hf = initial energy (e.g -13.6 ev at n=1) - final energy (-3.4ev atn=2)
state the assumptions of the theory of special relativity and outlineevidence for the invariance of the speed of light
Physical laws have the same form in all inertial frames (frame ofreference which obeys newtons first law)The speed of light in free space is constant(/invariant)3 key points of evidence:
Time Dilation - a moving clock runs slower then a clock that isstationaryLength Contraction - a rod moving in the same direction as it'slength appears shorter when movingRelativistic Mass - mass of an object increases with velocity
use E=mc2 and the relativistic equations for length contraction, time
Chapter 30 | Nuclear Energy
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dilation and mass increase
Einstein's relativistic mass formula shows no object can reach thespeed of light because at that point the mass would be infiniteSupplying any form of energy to an object increases it's mass withaccordance to E=mc2
sketch the binding energy curve and carry out energy calculationsfor nuclear reactions
The mass of separated nucleons is always greater than the mass ofthe combined mass of the nucleusmass defect is the difference between the mass of separatednucleons and the combined mass of the nucleus1u = 1.66*10^-27 = 931 MeVbinding energy of a nucleus is defined as the work done to separatea nucleus into its constituent neutrons and protonsbinding energy curve is the plot of all known isotopes's bindingenergy against their mass number
most stable isotope is at A = 50 as the binding energy is the greatestherethe nucleons are not as bound together at the maximumwhen a large nucleus disintegrates each nucleon becomes part of asmaller hence B.E. per nucleon increases.the nucleons in the product nucleus are far more tightly bound so theenergy released during the disintegration is equal to the increase inB.E.
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the loss of P.E. (and increase of B.E.) is released as K.E.in fission a large nucleus disintegrates into two equal smaller nucleiradioactive disintegration occurs where the original nucleus lossesan alpha, beta or gamma particle.
where an alpha & beta particle are released both lead to anincrease of B.E. per nucleon and hence release energy as K.E.of the products
Fusion occurs when two light nuclei join together with a massnumber of less than 50. The B.E. per nucleon is increased so energyis released when the nucleons fuse together
explain the origin of the neutrino hypothesis
Puali suggested that an additional particle called a neutrino is alsoemitted during beta decay which is responsible for missing energyif the neutrinos share of the energy is negligible then the betaparticle's K.E. is almost equal to Q because it's much lighter than therecoil nucleus.
Hence K.E. max is equal to Q.
describe the principles of nuclear fission
uranium nucleus splits into two, each of it's nucleons becomes a partof a nucleus about half it's size hence the B.E. per nucleon increasesby roughly 1 MeV. So, approximately 1 MeV of kinetic energy isreleased and since uranium as around 200 nucleons that means 200MeV being released - this is a lot.a single uranium nucleus might release two more neutrons whichcan bombard and cause fission to two more radioactive nuclei whichrelease more neutrons which do the same. This process is a nuclearchain reaction.
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describe the main features of the thermal nuclear reactor
critical mass of fuelthe minimum mass capable of producing a self sustaining chainreaction
choice of moderatordo not absorb the released neutrons but help to scatter them
choice of control rodabsorb neutrons rather than scatter them
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type of coolantpumped from the core of the reactor to the heat exchangerwhere where it's used to produce steam to drive the turbines
treatment of wastein the form of spent fuel and fuel cans
it's radioactive
safe storage and cooling of fuel rods as they get extremely hotwhen radioactivespent fuel is removed from cans and reprocessed to recoverany fuelunwanted material is stored is sealed containers until it is nolonger radioactive
describe the principle of the fast breeder reactor
Makes use of U-238 which makes up 99% of natural uranium andplutoniumPu is fast fission by neutrons without the need of a moderatorit's surrounded by U-238 nucleiwhen the Pu releases a neutron from disintegrating; it is absorbed byU-238 which becomes Pu creating a chain reaction.
explain energy release due to nuclear fusion
Essentially, after the two light nuclei fuse the binding energy of theproduct nucleus is greater than the of the initial hence energy isreleased
describe the main difficulties associated with a fusion reactor
Plasma Heating - Needs lots of electricity to reach the temperaturesneeded for plasma which easily conducts electricity.Plasma Confinement - Plasma will melt anything it touchestherefore it must be confined. Current methods include using anelectromagnetic field however it is difficult to restrict the plasma'smovement.
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