1.1. To provide an exam “crib sheet” for the EMPA To provide an exam “crib sheet” for the EMPA practical exams (Unit 3 and Unit 6) by reverse practical exams (Unit 3 and Unit 6) by reverse engineering the previous mark schemesengineering the previous mark schemes

2.2. To avoid losing marks for silly mistooks and to To avoid losing marks for silly mistooks and to “take the hit” for the odd hard mark lost“take the hit” for the odd hard mark lost

References :References : Unit 3 SpecimenUnit 3 SpecimenUnit 3 June 2009Unit 3 June 2009Unit 6 SpecimenUnit 6 Specimen

This is the first thing you will do when you enter the room!

There is typically a 8 or 9 mark planning question in There is typically a 8 or 9 mark planning question in the part 2 written part of the EMPA, they look easy the part 2 written part of the EMPA, they look easy but are normally answered badly (half marks at best)but are normally answered badly (half marks at best)

Your answer needs to be structured and complete. Old Your answer needs to be structured and complete. Old style mark schemes adopted the following structure style mark schemes adopted the following structure which is reasonablewhich is reasonable

1.1.MeasurementsMeasurements

2.2.Strategy (method)Strategy (method)

3.3.ControlControl

4.4.DifficultiesDifficulties

1.1. MeasurementsMeasurements

State all the measurements which need to be taken State all the measurements which need to be taken and the piece of apparatus used to take the and the piece of apparatus used to take the reading.reading.

Especially remember the obvious ones, rulers, Especially remember the obvious ones, rulers, balances and stopwatchesbalances and stopwatches

Take care to consider multiple readings (mean) Take care to consider multiple readings (mean) especially for measurements such as diameters especially for measurements such as diameters taken with a micrometer taken with a micrometer

2. Strategy (method)2. Strategy (method)

A detailed description of how to conduct the experiment, A detailed description of how to conduct the experiment, which explains how to use your measurements to achieve which explains how to use your measurements to achieve the objective. Connect with underlying Physics and Maths the objective. Connect with underlying Physics and Maths equations e.g. Diameter to area calculationequations e.g. Diameter to area calculation

Usually, your method should suggest a graph being Usually, your method should suggest a graph being plotted (details of axis etc) and will probably use the plotted (details of axis etc) and will probably use the gradient and/or intercept to produce the result you’ve gradient and/or intercept to produce the result you’ve been asked to findbeen asked to find

Remember repeat readings and mean averagesRemember repeat readings and mean averages

Remember use of set squares, protractors and plumb Remember use of set squares, protractors and plumb bobs to establish “squareness”bobs to establish “squareness”

3. Control3. Control

Remember to describe the things you will keep the Remember to describe the things you will keep the same.same.

Your practical should only have a single Your practical should only have a single independent variableindependent variable

Some of this may discuss limiting environmental Some of this may discuss limiting environmental change such as temperature and draughts etcchange such as temperature and draughts etc

4. Difficulties4. Difficulties

Describe what the difficulties may be and how to Describe what the difficulties may be and how to limit or overcome their effectlimit or overcome their effect

Multiple readings and mean (Especially diameters)Multiple readings and mean (Especially diameters)

Reduce uncertainties by making readings as large Reduce uncertainties by making readings as large as possibleas possible

Reduce parallax errorsReduce parallax errors

Take care with “squareness” and “parallelness”. Take care with “squareness” and “parallelness”. Either use set square, protractor, plumb bob or Either use set square, protractor, plumb bob or perhaps multiple readings at several pointsperhaps multiple readings at several points

4. Difficulties4. Difficulties

Note:-Note:-

If you use “taking repeat readings and average” as a If you use “taking repeat readings and average” as a suggestion for how to overcome a difficulty.suggestion for how to overcome a difficulty.

Don’t say “To make my results better”Don’t say “To make my results better”

Say “To reduce uncertainties and identify anomalous Say “To reduce uncertainties and identify anomalous readings”readings”

Taking readingsTaking readings

Ensure that all readings are taken to the precision of Ensure that all readings are taken to the precision of the instrument used (e.g. To the nearest mm for the instrument used (e.g. To the nearest mm for ruler or degree for a protractor)ruler or degree for a protractor)

Ensure that the same number of significant figures are Ensure that the same number of significant figures are used... 2.3cm, 3.4cm & 1cm (1cm should be 1.0cm)used... 2.3cm, 3.4cm & 1cm (1cm should be 1.0cm)

Take care with the number of sets of readings, often Take care with the number of sets of readings, often instructions are unclear... Phrases such as “take 4 instructions are unclear... Phrases such as “take 4 readings” often mean 4 more readings in addition readings” often mean 4 more readings in addition to the one initially taken during the detailed to the one initially taken during the detailed descriptiondescription

If in doubt take one more set! Remember a graph If in doubt take one more set! Remember a graph needs an absolute minimum of 5 readingsneeds an absolute minimum of 5 readings

IF IN DOUBT TAKE REPEAT READING SETS AND FIND IF IN DOUBT TAKE REPEAT READING SETS AND FIND THE MEAN (YOU HAVE THE TIME)THE MEAN (YOU HAVE THE TIME)

Ensure that you have a good range of results. Not a Ensure that you have a good range of results. Not a bad idea to play firstbad idea to play first

Discussing readingsDiscussing readings

Often you will be asked to describe how you took Often you will be asked to describe how you took certain readings... Often the correct answer involves certain readings... Often the correct answer involves the use of a set square, protractor, plum bob, multiple the use of a set square, protractor, plum bob, multiple readings to ensure things are parallel or finding the readings to ensure things are parallel or finding the midpoint of something midpoint of something

““Things may not be in the same planeThings may not be in the same plane”, “squashing ”, “squashing things with a micrometer”things with a micrometer”

Tabulating ResultsTabulating Results

Ensure that independent variable is in the 1Ensure that independent variable is in the 1stst column column

x/mmx/mm y/gy/g z/Vz/V

Note the way the unit is shown as “dividing” the Note the way the unit is shown as “dividing” the quantity. This is how AQA want itquantity. This is how AQA want it

If you have to add a column for measurements raised If you have to add a column for measurements raised to a higher power (e.g. Tto a higher power (e.g. T44 or x or x22), then remember to ), then remember to quote those raised values to 3 s.f., 2 s.f. is not quote those raised values to 3 s.f., 2 s.f. is not enough.enough.

Size : As large as possible (at least 8x8). Remember there are Size : As large as possible (at least 8x8). Remember there are 4 combinations of axis/paper orientation4 combinations of axis/paper orientation

False origin (i.e. Axis only consider the data range) may be okFalse origin (i.e. Axis only consider the data range) may be ok

Sharp pencil : single sharp linesSharp pencil : single sharp lines

Double check you have the axis as instructed, (often the Double check you have the axis as instructed, (often the independent variable along the bottom)independent variable along the bottom)

Sensible scale (1,2,5,10 etc per box not 3, 7, 19 etc)Sensible scale (1,2,5,10 etc per box not 3, 7, 19 etc)

Label each axis with quantity and unit (x/mm)Label each axis with quantity and unit (x/mm)

TitleTitle

All points plotted correctly (double check) small All points plotted correctly (double check) small vertical/horizontal cross recommended to the nearest mmvertical/horizontal cross recommended to the nearest mm

Single clean line of best fit (label this as line of best fit)Single clean line of best fit (label this as line of best fit)

Remember if the line must pass though the origin then Remember if the line must pass though the origin then the line of best fit is effectively “a radius” you can the line of best fit is effectively “a radius” you can change the angle not the horizontal or vertical offsetchange the angle not the horizontal or vertical offset

Often ideally each data point should be Often ideally each data point should be 2mm from 2mm from the line of best fit. Jolly hard! Do not panic! Double the line of best fit. Jolly hard! Do not panic! Double check plotting and check plotting and possiblypossibly double check anomalies double check anomalies

Gradient : As large as possible (> 8x8), construction Gradient : As large as possible (> 8x8), construction lines shown, show lines shown, show y & y & x on the graph with unitsx on the graph with units

If tangent is required, still meet 8x8 criteriaIf tangent is required, still meet 8x8 criteria

Part B : The written practical paperPart B : The written practical paper

Remember “state and explain” can hide 2 marksRemember “state and explain” can hide 2 marks

Often you will be asked which result has the greatest Often you will be asked which result has the greatest percentage uncertainty.... For a fixed absolute percentage uncertainty.... For a fixed absolute uncertainty... This will be your smallest readinguncertainty... This will be your smallest reading

Calculating the percentage uncertainty (we await AQA)Calculating the percentage uncertainty (we await AQA)

Show working (as always)Show working (as always)

You may be asked to comment upon the validity of a given You may be asked to comment upon the validity of a given uncertainty.... i.e. Compare a predicted uncertainty with uncertainty.... i.e. Compare a predicted uncertainty with one found from the range in a set of results one found from the range in a set of results (USE MY (USE MY UNCERTAINTY NOTES ONCE FIXED)UNCERTAINTY NOTES ONCE FIXED)