1

GCE 2008 PHYSICS

UNIT 6PH06/ 1A & 1B

Notes on Assessment Criteria This document contains the Principal Moderator’s comments on the assessment criteria and is intended to be used by teaching staff only. This document must not be provided to candidates. Candidates should be using the assessment criteria grid which can be found in GCE 2008 Physics specification. November 2011

2

GCE Physics 6PH06 MARKING GRID A: Planning Ref Criterion

Notes on awarding the mark

P1 Identifies the most appropriate apparatus required for the practical in advance

A list of the basic equipment is sufficient

P2 Provides clear details of apparatus required including approximate dimensions and/or component values (for example, dimensions of items such as card or string, value of resistor)

Meter ranges, number and size of masses, dimensions of card and mass of bob are expected. Candidates should select the range of variables. List should enable correct apparatus to be supplied without further explanation. The apparatus list and diagram can provide some evidence as this is a development of P1 & P3. All the evidence for P1 – 3 should be in the same area.

P3 Draws an appropriately labelled diagram of the apparatus to be used

Must be informative. Diagrams should be dimensioned where appropriate and labelled and, for example, rulers should be drawn close to the measured length. Given P1, 2 & 3 could another candidate do the experiment as planned?

P4 States how to measure one quantity using the most appropriate instrument

Any quantity but candidate must clearly state ‘..use this to measure that...’, the examiner will not make assumptions as to what the candidate means

P5 Explains the choice of the measuring instrument with reference to the scale of the instrument as appropriate and/or the number of measurements to be taken

Must explain why choice is appropriate in the context of the measurement to be made and not simply state the precision. It is not enough to quote either the range or the precision, or both, without reference to the experiment. E.g. ‘A stopclock has a precision of 0.01 s which is less than the uncertainty of the manual operator which is likely to be 0.1 s. Or, ‘the uncertainty of 0.005 V in a meter gives a % uncertainty of 0.7%’ in a typical measurement of 0.7 V as in the forward bias voltage of the diode in this experiment.

3

P6 States how to measure a second quantity using the most appropriate instrument

Same as P4, any quantity. It does NOT have to be one of the variables eg resistance of the resistor used in ‘Crossing the Tracks’.

P7 Explains the choice of the second measuring instrument with reference to the scale of the instrument as appropriate and/or the number of measurements to be taken

Same as P5

P8 Demonstrates knowledge of correct measuring techniques

Anything that improves the measurement ie outcome of the experiment – see Tutor Support Materials. Good candidates draw on their own previous experiences when planning the readings. A timing marker at the centre of an oscillation is one technique and another is using the laptimer to record the time when the potential difference reaches a certain value. The technique should improve the measurement and be explained.

P9 Identifies and states how to control all other relevant quantities to make it a fair test

Expect a correct context. Look for A0 in pendulum and ‘initial voltage’ in ‘tracks’. Relevant quantities is the key here. If there are none to control the candidate should explain why. Those not controllable, like room temperature, can be measured before and after the work, if a change in them is likely to affect the outcome.

P10 Comments on whether repeat readings are appropriate for this experiment

A development of P8 and the key word is comments candidates distinguish between method and reading. If repeat readings are not appropriate this must be stated. Repeating the whole method might then be suitable. Comments should relate to the reliability and accuracy of the data in the context of the work and to the use of mean values. It is not enough simply to say that repeats will be taken.

P11 Comments on all relevant safety aspects of the experiment

Credit sensible comments only when justified. If there are no safety concerns then that should be explained – 12 V electricity is safe because it will not give the careless user a shock. The power supply unit might need more thought however.

4

P12 Discusses how the data collected will be used

Do not allow ‘plot a graph’ alone. Deriving formula for graph is done here. In effect a comparison with the equation of a straight line is expected. They must show how they will find the answer the briefing asks for. Deriving the experimental equation will help with A10 too.

P13 Identifies the main sources of uncertainty and/or systematic error

Referring to method as well as measurement. This looks forward to what will be done in the experiment and A12 looks back at what was done.

P14 Plan contains few grammatical or spelling errors

Consider the scientific terms and explanations of techniques and method.

P15 Plan is structured using appropriate subheadings

Expect three. Many good candidates follow the marking grid – which is fine – but some headings are still needed.

P16 Plan is clear on first reading

Is the written communication clear? Clarity in describing the actual method is what is looked for. Must effectively state somewhere ‘...vary this and measure that...’ A surprisingly high number of candidates do not provide a method.

Maximum marks for this section

16

5

B: Implementation and measurements

Ref Criterion

Notes on awarding the mark

M1 Records all measurements with appropriate precision, using a table where appropriate

The numbers should show the precision of the measuring instrument referred to in P5 & P7. Time should be to at least 0.1 second ie NOT 10, 20, should be 10.0, 20.0 etc. The candidate should write down the reading on the instrument without processing.

M2 Readings show appreciation of uncertainty

Should show ± at top or bottom of table. Candidates are expected to appreciate the uncertainty in what they are actually reading.

M3 Uses correct units throughout measurement

This is for using correct units throughout measurement

M4 Refers to initial plan while working and modifies if appropriate

If no modifications are done candidates must justify this. Candidates might consider the ranges suggested for P2. Ignore trivial changes or obvious flaws in plan.

M5 Obtains an appropriate number of measurements

Usually 6 to plot a linear graph - expect repeats where method suggests these

M6 Obtains measurements over an appropriate range

For the variables used, candidate should review results critically. One variable should double/halve.

Maximum marks for this section

6

6

C: Analysis Ref Criterion

Notes on awarding the mark

A1 Produces a graph with appropriate axes (including units)

Must include units. The quantity plotted determines the units of the gradient, so logarithmic quantities must be dimensionless. E.g. ln (x/m).

A2 Produces a graph using appropriate scales

Data must occupy half of page on both axes. Scales must be simple so that gradient calculations and interpolation are easy – not 3’s or 7’s.

A3 Plots points accurately

Look at points not on the BFL (Best Fit Line) – at least 2 points should be checked. Must be accurate to 1 mm. Plots checked should be underscored if correct or ringed if incorrect

A4 Draws line of best fit (either a straight line or a smooth curve)

Expect a good line at this level. BFLs will usually have plots on both sides and will not be forced through the origin.

A5 Derives relation between two variables or determines constant

This is for the gradient calculation and linking this to the constant.

A6 Processes and displays data appropriately to obtain a straight line where possible, for example, using a log/log graph

Evidence is the appropriate graph showing data that has been processed and usually follows from P12.

A7 Determines gradient using large triangle

Must not use tabulated values unless plots are exactly on BFL. Triangle must occupy at least half of the drawn line. Measurement must be correct to one small square - with negative sign as appropriate. If the data is a curve a straight line may be drawn on part of the data as an approximation described by the candidate to enable them to gain this and the next mark.

A8 Uses gradient with correct units

Must see a gradient unit somewhere and the unit for any constant. There might be no unit, as in a log-log graph.

7

A9 Uses appropriate number of significant figures throughout calculations

These might derive from P5 & P7. Candidates should use 3 (or very occasionally 2) SF in recording data, plotting graphs, gradient calculations and final answers

A10 Uses relevant physics principles correctly

This mark is for good physics seen anywhere such as mention of SHM, radiation flux or whatever is appropriate to the context. Can be awarded for extra maths as directed by briefing, such as the log expansion of the equation, if sufficiently detailed.

A11 Uses the terms precision and either accuracy or sensitivity appropriately

Seen anywhere, including in the plan. Do not award if a contradiction is seen.

A12 Discusses more than one source of error qualitatively

This is a review of P13 and should refer to method and readings. Must be based on evidence from experiment(method)/results/graph. This is a review of the uncertainty in the light of the experience of doing the experiment, not merely a restatement of P13.

A13 Calculates errors quantitatively

Expect %U in appropriate measurements but at least the dependent variable.

A14 Compounds errors correctly

Can be adding %U as appropriate or use of error bars, and must refer to the result or graph. Error bars to generate 2 lines resulting in % difference of gradients is a good way to combine uncertainties when logarithms are used.

A15 Discusses realistic modifications to reduce error/improve experiment

Must be practical in a well resourced school laboratory. Allow datalogger if the improvement is described fully.

A16 States a valid conclusion clearly

Refer to the aim given in briefing, so can be mathematical. Evidence must be quoted somewhere

A17 Discusses final conclusion in relation to original aim of experiment

Candidates should consider the validity and/or reliability of their conclusion. Best is comparing %D with %U but they could discuss the goodness of fit of BFL.

8

A18 Suggests relevant further work

Must be non-trivial and develop idea behind practical work. Further work should be both relevant and realistic. It should aim to be the non-trivial follow-up experiment that could be performed by the same student in the same laboratory. Comments must be scientific not holistic.

Maximum marks for this section

18

Total marks for this unit

40

The key words in the criteria are ‘Discuss’, ‘Comment’ and ‘Suggest’. Candidates must do more than state a fact for the award of these marks.