A-level Physics P5

CAMBRIDGE INTERNATIONAL EXAMINATIONS

Compiled by Imran Mirza MSc Physics, PGCC, Scoland, Uk

Planning Analysis And Evaluation

A-level Physics This booklet covers CIE A Level Physics Paper 5 By Imran Mirza

2009-2011

Exam tips for Planning, Analysis and Evaluation paper By Imran Mirza Don't rush........ Three golden rules........ 1. Read the question 2. READ the question 3. Answer the question Make sure that you do not do what so many students do......they see a 'key c word like 'magnetic flux' in a question and write down everything they know about magnetic flux, as fast as they can. Take your time..........there is more than you think!

IT is forbidden........... Marks will not be awarded to answers which are unclear. Try to write a reason for your choice of apparatus and.....

Don't be intimidated........ Don't be intimidated by long questions...... they quite often are easier and quicker questions than the shorter ones...........

Do as you are told!  Write the apparatus along with reason. Remember that not all of the apparatus in the provided list is essential for the investigation- You may use other standard equipment that is needed/ available in the laboratory work. 

Draw a neat and labeled diagram of the arrangement of apparatus which you propose to use. Space is available for this in the question paper.

 Write procedure in steps wise and high light control of certain variables to carry out a valid

investigation.

Write the safety aspect (where appropriate) of your investigation. Sometimes the question specifically ask for these to be mentioned (e.g. in a design question where radioactive sources are used) but any relevant safety point can be rewarded. A number of marks are reserved for what is considered to be good further or relevant detail. This is because your answers depend so much on the approach which has been taken!

Keep in mind! Some students write copious amounts about the 'conclusions* of their investigation and draw sketch graphs of what the result might be. Since no experimental work has actually been carried out it is not possible to reward any work of this kind Good marks can often be gained by giving relatively short concise answers. Keep an eye on the time (watch)

Blank paper does not score Do not leave anything out! If you have no idea what the question is on about....... GUESS. You never know.... You just might be right! .........and don't give up........ Work right through to the end of the exam. Cross checking your answers......... keep thinking........ New ideas may draw! Stay Cool......

Nobody knows everything.......... .......so don't panic if a question is not well answered. ........just do what you can........

The important thing is that you walk out at the en4 thinking.........

“I DID MY BEST”

Instructions In the Syllabus

Paper 5 This paper will consist of two questions of equal mark value (15 marks each) based on the practical skills of planning, analysis and evaluation. The examiners will not be restricted by the subject content. Candidates will answer all questions. Candidates will answer on the question paper. Paper 5

Type of paper Duration Planning, Analysis 1 h 15 minutes & Evaluation

Marks 30

Weighting 12%

Mark scheme for Paper 5 Paper 5 will be marked using the broad mark scheme below. The expectations for each mark category are listed in the sections that follow. Question 1 Skill Planning

15 marks

Breakdown of marks Defining the problem Methods of data collection Method of analysis Safety considerations Additional detail

3 marks 5 marks

2 marks 1 mark 4 marks

Question 2 Skill Analysis, conclusions and evaluation

15 marks

Breakdown of marks Approach to data analysis Table of results Graph Conclusion Treatment of errors

1 mark 2 marks 3 marks 4 marks 5 marks

Planning Defining the problem Candidates should be able to:  Identify the independent variable in the experiment……….  Identify the dependent variable in the experiment……….  identify the variables that are to be controlled…………. Methods of data collection Candidates should be able to:  describe the method to be used to vary the indepepdent-variable;  describe how the independent and dependent variables are to be measured;  describe how other variables are to be controlled;  describe, with the aid of a clear labeled diagram, the arrangement of an apparatus for the experiment and the procedures to be followed. For full marks to be scored in this section, the overall arrangement must be workable, that is, it should be possible to collect the data required without undue difficulty if tie apparatus were assembled as described. The measuring instruments chosen should be fit for purpose, in that they should measure the correct physical quantity to a suitable precision for the experiment.

Method Of analysis

Candidates should be able to: • describe how the data should be used in order to reach a conclusion, including details of derived quantities to be calculated and graphs to be drawn as appropriate. Safety considerations

Candidates should be able to: • assess the risks of their experiment; • describe precautions that should be taken to keep risks to a minimum. Additional detail

Up to three marks will be available for additional relevant detail. How these marks are awarded will depend on the experiment that is to be planned, but they might for example include marks for ! describing the control of additional variables, or for a diagram of a circuit needed to make a particular measurement, or for additional safety considerations. j Analysis, conclusions and evaluation Approach to data analysis Candidates should be able to: • rearrange expressions into the forms y = mx + c, y = axn, and y = aekx ; • plot a graph of y against x and use the graph to find the constants m and c in an equation of the form y = mx + c • plot a graph of log y against log x and use the graph to find the constants a and n in an equation of the form y = axn; • plot a graph of In y against x and use the graph to find the constants a and k in an equation of the form y = aekx; • decide what derived quantities to calculate from raw data in order to enable an appropriate graph to be plotted. Table of results Candidates should be able to: • complete a table of results following the conventions required for Paper 3; Where logarithms are required, units should be shown with the quantity whose logarithm is being taken, e.g. In (d/cm). The logarithm itself does not have a unit Graph Candidates should be able to: • plot a graph following the conventions required for Paper 3; • show error bars, in both directions where appropriate, for each point on the graph; • draw a best-fit straight line and a worst acceptable straight line through the points on the graph. The worst acceptable line should be either the steepest possible line or the shallowest possible line that passes through the error bars of all the data points. It should be distinguished from the best-fit line either by being drawn as a broken line or by being clearly labelled.

Conclusion Candidates should be able to: • determine the gradient and y-intercept of a straight-line graph; • derive expressions that equate to the gradient or the y-intercept of their best-fit straight lines; • draw the required conclusions from these expressions. The conclusion required will normally be the value of a constant

Candidates should be able to:  convert absolute error estimates into fractional or percentage error estimates and vice versa;  show error estimates, in absolute terms, beside every value in a table of results;  calculate error estimates in derived quantities;  show error estimates as error bars on a graph;  estimate the absolute error in the gradient of a graph by recalling that absolute error = gradient of best-fit line - gradient of worst acceptable line;  estimate the absolute error in the y-intercept of a graph by recalling that absolute error = y-intercept of best-fit line - y-intercept of worst acceptable line;  express a quantity as a value, an error estimate and a unit

Q1. A fine wire mesh has individual wires that are spaced very close together. See flg. 1.1.

Fig. 1.1

The mesh behaves like two diffraction gratings placed at right angles to each other. The diffraction grating formula is d sin θ= n λ The spacing between the wires of the mesh is to be found accurately. Design a laboratory experiment using light of a single wavelength to determine the spacing between the wires. You may assume that the wavelength of the light is known. You should draw a detailed labeled diagram showing the arrangement of your apparatus. In your account you should pay particular attention to (a) the type of light source to be used, giving a reason for your choke, (b) the procedure to be followed and the measurements that would be taken, (c) how the measurements would be used to find values of 0, (d) how the spacing between the wires would be deduced, (e) any safety precautions you may take.

Marking key:

Diagram of arrangement (light source/mesh/screen or collimator/mesh/telescope)

[1]

Fringes or dots shown on screen. May be shown on diagram.

[1]

Some sensible discussion of coherence

[1]

Use of laser or single slit (and lens) in collimator Measurements: distance from mesh to screen and separation between fringes OR measure an angle from the spectrometer table

[1] [1]

n = 1; find separation between central fringe and first bright fringe OR measure angle between central bright beam and first order beam using scale on table

[1]

Use of dsinθ = nλ to find d. n must be clearly identified

[1]

Any safety precaution e.g. use goggles/do not look directly into laser beam/cover over sodium lamp do not touch the bulb [1]

Any good/further detail Examples of creditworthy points might be: Take readings with mesh in different positions to average d Sketch/suggestion of two-dimensional array of dots on screen Laser + mesh 4- screen all at same height X = 589 nm for sodium lamp or about K = 630 nm for He/Ne laser/semiconductor laser

[2]

of the order of 1 m to 4 m (laser method) Measure 20 and 4ivide by two to reduce uncertainty in 0 Repeat experiment with 2nd order (3rd order etc.) beams Detail relating to setup/use of spectrometer

Allow other valid points. [Total: 10 marks] Report:

In this question candidates were required to design a laboratory experiment to investigate how to determine the spacing between wires of a fine mesh using light of a single wavelength. It was expected that candidates would show a labelled diagram of the setup showing a light source, a wire mesh and a screen. It was expected that candidates would be able to identify a source giving monochromatic light from a point source (e.g. laser, Sodium lamp plus slit to name a few possibilities). Weak candidates used ultra-violet, infra-red, gamma, alpha, microwaves or 'white monochromatic light'; Some candidates used a light bulb which when combined with a filter and a slit was credited. Many candidates responded with a double slit setup or used a diffraction grating instead of the wire mesh which was not credited. The best candidates realised that the pattern produced on the screen would be a rectangular array of bright dots (candidates were not required to work this out). Answers that

referred to crossed patterns of lines or to circular fringes were allowed. Weak candidates showed no pattern at all or made no reference to a pattern within the written text. It was expected that candidates would state the quantities they would measure in order to find 0. Many candidates used a protractor without credit (indicating candidates did not appreciate the size of angles involved). Good candidates said they would measure D, the mesh to screen distance, and x, the dot separation. Good candidates took these measurements and used tan θ = x/D to find θ and subsequently used d sin θ= n λ (where n = 1) to find d. Weaker candidates confused the symbols and their meaning, for example ‘d’, instead of being the 'spacing between the wires', became 'the distance between the mesh and the screen. Also many candidates thought d = I/spacing. It was expected that n would be given a value (e.g. n = 1) in order to use the equation d sin θ= n λ. Vague comments about the 'order of a fringe' did not gain credit Some strong candidates labelled a spectrometer and gained marks for taking the angle from the table and saying how they did this in detail. Some good candidates suggested plotting n λ, against sin θ to get d from the gradient.

A good well-annotated diagram could gain up to half marks for this question, whereas a poor one often received little or no credit Sensible safety ideas only were given credit (e.g. 'do not look at the source directly' or 'use goggles to prevent damage to eyes'). 'Do not point laser at skin as it will burn' was not credited. Marks were available for good further detail. Many candidates were able to access these marks. No credit was given for a darkened room as coherent light will produce visible fringes in a classroom. However, few candidates appreciated the need for a coherent source.