Y13 Page

 

   Information for Y13 (2015/16)

Greetings! I am Mrs. L. Jones.

I was Head of Physics at WGHS in the olden days.... I have taught this A level course (under several slightly different wordings) since before you were born.

My Cyberphysics site is used by an average of 5000 students a day during term time. I started it as a means of communicating background info with my students, notes, solutions to homework, questions, revision lists etc. got added (saving on photocopying!) and it snowballed.

I will use it to communicate with you.... it will provide you with notes and background, but the main advantage is the interactive syllabus.

This page is only linked from the index page - via the dropdown 'Exam Prepapration' Menu.

I shall be tackling Unit 5 with you...

My lessons with you are:

Week A - Wednesday (period 1) in lab S5 and Friday (period 4) in lab S5

Week B - Wednesday (period 2) in lab S5 and Friday (period 5) in lab S5

I am only in school on those days - I am only teaching sixth-form. I do not have a form. It is pointless to put notes for me in a pigeon hole.

Communicate with me in lessons or via e-mail: lJones@wghs.org.uk

Lesson/teaching structure.

I will collect homework in on a Wednesday. I will feedback on it on the following Friday. Homework not handed in on time will therefore not be marked as solutions will have been issued. If you fail to hand in homework three times in a term I will refer you to the Head of Sixth form so that senior management are aware of the problem.

Each Friday (after the third week) there will be timed past examination questions on the sections we have completed (all of them - not just the most recent!). These will colour my view of your progress more than the homework tasks, the completion of homework tasks will colour my view of your effort in the subject.

Absence

The proposed program for how we will cover the material is set out below. If you are absent there will be enough information here for you to do some studying at home. You are expected to work through the material as soon as possible. It is your responsibility to ensure there are no gaps in your learning.

If I am absent for any reason I will enter the work that you should do on this page. Therefore there is no excuse that you did not know what to do!

Homework will be set on a Friday and collected in the following Wednesday in class.

Details of homework set will be found on this page on the evening it has been set.

There are two sections of Unit 5 that we have to cover:

Radioactivity

Nuclear

Links to A level standard questions can be found on those pages as hyperlinks.

I suggest that when revising you work though the section notes by using the links - you might find a hard copy useful. Then tackle at least one of the questions to see how well you have understood it. Full solutions are there for you.

Be honest with yourself. You have nothing to gain by pretending you can do a section.

If you get full marks on a couple of qustions then it is probably not worth spending more time at this stage on that topic. If you have difficulty look carefully at my solution and try another question.

CLASSWORK summary and HOMEWORK Tasks

Date (week beginning)

Classwork Summary

HW

4th January 2016

The Atom: Evidence for the nucleus:

A qualitative study of Rutherford Scattering

Explain how Rutherford's experiment made us rethink what atoms were like

Understand the function of the parts of the equipment used.

Know the observations made and what they made Rutherford understand about the atom.

Background radiation; its origins

 

Read and make notes on Rutherford scattering

Review radioactivity at GCSE

11th January 2016

Radioactivity Basics:

Radioactivity α, β and γ their properties and experimental identificationapplications, e.g. to relative hazards of exposure to humans

The experimental investigation of the inverse square law for γ rays

Applications, e.g. to safe handling of radioactive sources

Background radiation; its origins and experimental elimination from calculations

recall the charge, masspenetration power (hence how to distinguish them) and ionizing power of each type of radiation

recall how to perform an experiment using a radioactive source safely.

Explain how the ISL relates to safety rule of keeping the source as far from you as possible.

Recall sources of background radiation and how to eliminate it from calculations and practical data.

Now try some A level questions on Rutherford's Experiment 

I will collect them in next Wednesday

18th January 2016

Random nature of decay - constant decay probability for a given nucleus 


Half-life and decay constant and their determination from graphical decay data including decay curves and log graphs; 


Applications, e.g. relevance to storage of waste radioactive materialsradioactive dating

recall that radioactive activity is:

spontaneous (probability of a decay cannot be changed by changing pressure/temperature etc.)

random - direction that ray is emitted or which nucleus will decay when - is impossible to say! But when dealing with large numbers of atoms the mathematics of probability can be employed.

Recall that radioactive decay is an exponential process therefore probability is applicable!

You should be able to

sketch a graph of number of nuclei against time (marking on multiples of No and T (half) to show th exponential relationship)

recall that the rate of decayN/t (or Activity of the sample) is proportional to the number of atoms of the radioisotope present in the sample.

Recall that the decay constant () is the constant of proportionality between activity and sample size. It gives a measure of the probability that a particular nucleus in a sample will decay in a given time. It has units of time-1.(The negative sign before it is because the number present decreases with time - so that would lead to a negative constant!)

recall that the half life of a radioisotope is the time taken for half of the radioactive nuclei of that isotope substance in a sample to decay. This is constant for any given isotope. The units are those of time.

appreciate the variation in natural half-lifes from nanoseconds to millions of years and the affect this has on uses and safeguards when disposing of waste.

know about carbon dating.

 

Now try some questions - I suggest Q4, Q6, Q8 and Q9 from this link 
25th January 2016

Mock Exam Week

1st February 2016

Variation of N with Z for stable and unstable nuclei

Graph of N against Z for stable and unstable nuclei

recall that Z is the atomic number (proton number)

sketch this graph - with labelled axes and values!

mark in alpha, beta and positron emitters

know that positron emitters are the result of artificial transmutation experiments

modes of decay - don't forget the neutrinos! - check out the Feynman diagrams that you did in module 1

decay equations should be most simple for you!

Test 1

Now try some questions - I suggest Q1, Q7 and Q10 from this link 
8th February 2016

Existence of nuclear excited states

γ ray emission

Application, e.g. use of technetium 99m as a gamma source in medical diagnosis

when the nucleus emits a radioactive particle the nucleons left are not all necessarily in their lowest possible energy state - they therefore emit a gamma ray as the 'rearrange' themselves into a more stable configuration

You should know the reasons why Tc99m is so valued and how it is used

Probing matter can be done by shooting particles into the nucleus (scattering) and making conclusions on its structure by what happens (recoil, deflection or the knocking out of another particle)

the Rutherford experiment did this!

As well as alpha particles high energy protons, neutrons, deuterium nuclei and electrons can be used

You should recall (from unit 4) how charged particles repel each other and be able to interpret the way that the particles produced make traces in a magnetic field (charged ones get deflected - use FLHR to determine the charge)

Test 2

Test 1 Feedback

15th February 2016
Half Term
22nd February 2016

Nuclear radius

Estimation of radius from closest approach of alpha particles and determination of radius from electron diffraction; knowledge of typical values

Dependence of radius on nucleon number


derived from experimental data

Calculation of nuclear density.

recall that the nucleus is measured in femtometres whereas the atom itself is of the order of angstrom units (10-10m)

probing matter can be done by shooting particles into the nucleus (scattering) and making conclusions on its structure by what happens (recoil, deflection or the knocking out of another particle)

See Rutherford expt. - as well as alpha particles high energy protons, neutrons, deuterium nuclei and electrons can be used to probe matter (remember particle accelerators as from unit 4?)

be able to interpret the way that the particles produced make traces in a magnetic field (charged ones get deflected - use FLHR to determine the charge)

understand that if an alpha particle is shot at a nucleus it will experience electrostatic repulsion and come to a stop a distance from the centre that depends on the charge in the nucleus and the kinetic energy of the particle projected at it.

be able to evaluate the distance of closest approach as the kinetic energy of the particle would be changes into potential energy at the point of closest approach

recall that the nucleus has a value of a few femtometres (in Rutherfords day it was thought to be of the order of 10-14m)

understand that measurements of nuclear size can be found from electron diffraction patterns (Sang page 11-13 and text book page 152 to 153)

know that nucleons are close-packed within the nucleus making all nuclei have the same density.

know what to plot as graphs from the equation to find ro

 

 

Now try some questions 

29th February 2016

Mass and energy

Simple calculations on nuclear transformations; mass difference;

binding energy

Atomic mass unit, u

Conversion of units; 1u = 931.1 MeV

Appreciation that E = mc2 applies to all energy changes

Graph of average binding energy per nucleon against nucleon number, A

How this applies to the Fission and fusion processes - see here for whole topic index

know that the mass of nuclear particles when associated together in a nucleus (and therefore all matter!) is less than the sum of the mass of the component parts.

know the difference in mass between individual consitituents and the associated particles is called the 'mass difference'

know that mass and energy are interchangable via the equation E = mc2 (Einstein's equation).

know that the conversion between mass (u) and energy (MeV) is possible via a shortcut in the databook that states the equivalence of mass and energy as: 1u = 931.1 MeV

Draw the graph of average binding energy per nucleon against nucleon number, A - including labelled axes with units and values on those axes!

Recall that fission is the splitting into two of a large nucleus and fusion is the fusing (joining into one) of two smaller nuclei.

Relate fission and fusion to the binding energy per nucleon graph to explain why the processes are energetically viable.

Test 2 Feedback

Test to try at home

(to be collected in Wednesday 9th March 2016)

7th March 2016

Induced fission by thermal neutrons

Possibility of a chain reaction

Critical mass

The functions of a moderator and the coolant in thermal nuclear reactors

Control of the reaction rate

Factors influencing choice of material for moderator, control rods and coolant

Examples of materials used (details of particular reactors are not required).

recall that a thermal neutron is a neutron that has energy in the infra red photon range.

know that if U235 absorbs a thermal neutron (becomes U236) it is very unstable and will split into two (not usually equal) nuclei

know that a couple (on average 2 to 3) of free neutrons are also produced (these can go on to produce more fissions). The fragments are more stable (energetically viable reaction) and energy is released when this happens.The resulting nuclei are called fission fragments NOTdaughter nuclei (that is the terminology in radioactivity!)

The freed neutrons can go on to produce further fissions, but are usually of too high energy to do this and need to be slowed down. This is done by a MODERATOR (moderates the speed of the neutrons!) such as graphite. It slows the neutron down by allowing multiple interactions (about 50) with the carbon lattice without absorbtion of the neutron into the carbon nucleus - graphite has a 'low cross section for neutrons'.

chain reaction is a reaction in which the instigator of the reaction is also produced as a product. It is therefore possible for the product of one reaction to go on to take the role of the reactant in a future reaction. Each fission produces neutrons that could go on to produce further fissions so the more atoms you have (greater mass of sample) the more likely that the reaction will continue in a chain reaction. But those neutrons are produced isotropically (equally in all directions) - the production direction is random, so an atom on the surface could well shoot off a neutron out of the Uranium mass and no fissions would then occur from them.

The bigger the surface area of the Uranium sample the more likely that neutrons will be sent out and not be able to make more fissions. As mass increases so does volume and surface area of the sample. A very small mass will have a larger surface area relative to its size than a bigger one so a chain reaction is less likely (greater proportion of its atoms will be on the surface). There is therefore a minimum mass that allows a chain reaction to occur. This is called the critical mass

it has a critical mass/surface area ratio below which a chain reaction is not viable. As 2/3 neutrons are produced each time a nucleus of Uranium splits the energy produced by reaction would escalate by a factor of about 2/3 at each stage. This would be uncontrolled acceleration of the reaction and be very dangerous (bomb). 

Control rods of cadmium or boron can be inserted into the reaction vessel to maintain the energy production at the required level. These have a 'high cross section for neutrons' - they absorb the neutrons, taking them out of the reaction preventing further fissions occuriing. The deeper the rods are inserted into the vessel the faster the rate at which energy is being produced will be diminished (more surface area of absorber - more absorbtion)

Moderator materials are chosen for low cross section for neutrons - don't absorb neutrons - interact to take kinetic energy from them instead.

Control rods are made of materials that absorb neutrons effectively - have a high cross section for neutrons.

Coolant (eg. water or CO2) needs to have a high specific heat capacityso that a large amount of heat energy can be absorbed without it getting too hot

Now try some questions 

Now try some questions for homework

and even more...

14th March 2016

Safety aspects:

Fuel used, shielding, emergency shutdown

Production, handling and storage of radioactive waste materials

Uranium is an alpha (and gamma!) emitter - uranium dust is very dangerous - highly localised ionisation in the body from alpha results in a high risk of cancer and mutaion in reproduction.

All forms of radiation are produced by the cocktail of fission fragments so shielding must be thick concrete (lead to expensive!)

Control rods contain enough absorbing material to completely shutdown the reactor - absorb so many neutrons that the chain reaction is stopped.

Fission fragments are radioactive isotopes of many elements - variety of half lives and type of radiation produced.

Neutron absorbtion by an atom creates a radioactive isotope of that element - which then decays into something else! So the reactor itself and instruments used within the reaction vessel become highly radioactive.

You should know about the three categories of waste (low, intermediate and high) due to their half lives (how long they will be dangerous for) and their activity, how they are dealt with (stored, monitored).

Also revise safety when dealing with radioactive materials for handling of active waste.

Now try some questions 

Test 3 Feedback

21st March 2016

No Friday Lesson

 
28th March 2016

Easter Break

4th April 2016
11th April 2016

Kinetic Theory - ideal gas - gas laws

Go through Mock Part 1

Gas laws as experimental relationships between p, V, T and the mass of the gas.

Concept of absolute zero of temperature.

Ideal gas equation (also called the 'Equation of State'):

pV = nRT for n moles

pV = NkT for N molecules.

Work done = p∆V

Avogadro constant NA

Molar gas constant R,

Boltzmann constant k

Molar mass and molecular mass.

 

 

- recall the properties of an ideal gas

- know that the nearest we have to an ideal gas is helium remote from its boiling point and at low pressure.

- use the equations to do calculations

- know that T must be in Kelvin!

- know that a mole is the Avogadro number of particles

- appreciate where absolute zero (-273oC becoming 0K) comes from (extrapolation of p/T and V/T graphs)

18th April 2016

Wednesday Lesson - EMPA

Kinetic theory - equations and derivation

Brownian motion as evidence for existence of atoms.

Explanation of relationships between p, V and T in terms of a simple molecular model.

Students should understand that the gas laws are empirical in nature whereas the kinetic theory model arises from theory.

Assumptions leading to

pV = 1/3Nm (crms) 2

including derivation of the equation and calculations. (A simple algebraic approach involving conservation of momentum is required).

Use of average molecular kinetic energy equation

Appreciation of how knowledge and understanding of the behaviour of a gas has changed over time.

Kinetic Theory Questions

- be able to sketch graphs of p against V, p against T, V against T

- know that NA is the number of particles in a mole of gas

- you have very few derivations to learn! Make sure you know this one well! You must learn the assumptions too and use words to explain how to derive it!

- understand how temperature of particles relates to their kinetic energy and mean square speed.

- internal energy of an ideal gas is only kinetic - it has (by definition no potential energy!)

- internal energy (sometimes called the random thermal energy) of a gas is the sum of kinetic energy and potential energy but the potential energy is so tiny that it can often be ignored. Potential energy is due to the interaction of neighbouring particles, this is therefore very significant in solids and liquids

- internal energy (sometimes called the random thermal energy) of a gas is the sum of kinetic energy and potential energy but the potential energy is so tiny that it can often be ignored. Potential energy is due to the interaction of neighbouring particles, this is therefore very significant in solids and liquids

- average molecular kinetic energy for a gas sample is directly proportional to absolute temperature in an ideal gas. (sketch the graph from the equation!)

- note that the Boltzmann constant k is simply R/NA

- the average molecular kinetic energy equation is for a single average molecule (to find the total energy for a gas sample you would have to multiply by nNA)

25th April 2016

Wednesday Lesson - EMPA

Questions on kinetic theory

 

 
2nd May 2016

Wednesday Lesson - EMPA

Last question in mock - kinetic theory

 
9th May 2016 Go through mock question  
16th May 2016 Leavers Service on the 17th - No physics lessons