.Dr. S.M.Harding
G496: Yr 13 Physics Practical
Investigation Pack
2009
A report of an extended investigation of a practical
problem related to physics or its applications. The practical
investigation should be carried out on any aspect of
physics of interest to you.
Walton High
Contents
Timeline ............................................................................................................................................................. 3
Outline of the task ............................................................................................................................................. 4
Practical Investigation ................................................................................................................................... 4
What are the aims? ....................................................................................................................................... 4
Managing the Practical Investigation ............................................................................................................ 4
Choosing a topic ................................................................................................................................................ 5
Preliminary work ............................................................................................................................................... 6
Doing your investigation.................................................................................................................................... 6
Things to do EVERY DAY ................................................................................................................................ 6
Things to do AT TH END OF THE FIRST WEEK ................................................................................................ 6
Things to do AT THE END OF THE SECOND WEEK ......................................................................................... 6
Writing it up ....................................................................................................................................................... 7
Investigation Checklist ....................................................................................................................................... 8
Dealing with uncertainties and errors ............................................................................................................... 9
Absolute, Relative and Percentage Uncertainties/Errors.............................................................................. 9
Quoting Uncertainties ................................................................................................................................. 10
Types of Uncertainties and Errors ............................................................................................................... 10
Systematic errors ..................................................................................................................................... 10
Random Uncertainties ............................................................................................................................. 10
Non-random Measurements ................................................................................................................... 10
Limited Sampling ..................................................................................................................................... 11
Manipulation of Independent Uncertainties............................................................................................... 11
Error bars on graphs .................................................................................................................................... 11
Markscheme .................................................................................................................................................... 13
List of titles ...................................................................................................................................................... 14
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Timeline
Fill in the dates that your teacher gives you:
Date
Submission of provisional titles
Submission of apparatus list
Practical work
Submission of draft report
Submission of final report
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Outline of the task
The Practical Investigation is expected to take about 10 hours of contact time and the associated
independent study time, and the Research Briefing about half of that. The two pieces of work together
form a coursework portfolio for which a single mark out of 30 is submitted making up the assessment Unit
G496.
Practical Investigation
Each candidate carries out an investigation of a practical problem related to physics or its applications. It is
anticipated that candidates will use a wide variety of experiments and techniques in this extended
investigation. The most suitable topic is a clearly defined problem, which offers scope for genuine
investigation, rather than routine, mechanical and unimaginative work. The topic chosen should afford the
candidate the opportunity to demonstrate understanding of physics at an Advanced GCE standard.
What are the aims?
One of the central features of the course is the emphasis placed on learning physics through the interplay
of theory and experiment – so that candidates understand where ideas come from, how they make sense
and how they may be used. This is made possible through the range and variety of illustrative experiments,
practical demonstrations and investigations that candidates meet during the course. But the importance of
the experimental work extends beyond the fulfilment of this objective. Many students will study more
science when they leave school or college, and there are some whose careers will involve science. An ability
to investigate an unfamiliar situation in a sensible and scientific way is an asset not only to these students,
but to all in tackling practical problems in everyday life. To this end, it is hoped that the development of
experimental and investigative skills is a significant feature of the Advancing Physics course.
Building on the AS Quality of Measurement task, it is expected that candidates should use skills developed
there, namely:
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recognize the qualities and limitations of measuring instruments, particularly resolution, sensitivity,
calibration, response time, stability and zero error;
identify and estimate the most important source of uncertainty in a measurement;
make effective plots to display relationships between measured quantities, including an
appropriate indication of uncertainty;
use simple plots of the distribution of measured values to estimate the median (or mean) value and
the spread (which may be estimated from the range of values), and to identify and account for
potential outlying values to quantify and enhance their investigation.
The outcome of the task is a written report that describes the process of the investigation and discusses the
conclusions that may be drawn from the practical work done.
Managing the Practical Investigation
To begin, the candidate chooses an interesting topic for investigation and carries out some preliminary
research – analysing the topic, getting 'a feel' for the relevant factors, considering the selection of
appropriate apparatus and measuring techniques, carrying out a literature search, if appropriate – with a
view to deciding upon an experimental design that will allow the first set(s) of readings to be taken.
The next stages are to carry out the Investigation in the laboratory, to write-up the findings of the
experimental work, in the form of a daily diary, and then to submit the finished report to the teacher for
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assessment. The assessment should be based on observation of the work done, and on discussion with the
candidate, as well as information revealed in the written report.
Choosing a topic
A good topic is…
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Something that you are interested in
Something that makes you think 'why does that do that?'
Something that is not a standard practical
Something that you do not know the answer before you start
Something that means that you will have to make something
Something that has scope for development
Something that mans you can make quality observations or take measurements or both
Something that includes physics!
A good investigation will incorporate a large number of the above points, but not necessarily all of them.
Start by looking around you and thinking about interesting things that you see. These tend to lend
themselves to mechanical properties type investigations (hair, spaghetti…), music (physics of the flute,
boxes under guitar strings) and such like. Alternatively it could be something that you have read about, a
toy you want to investigate, something you want to make.
The MOST important characteristic of this title is that it is OPEN. It must go somewhere, have room for
development or related work.
A list of titles is attached but you should be careful – just because it is on the list does not guarantee that
you will get on well with the idea. It will be tempting to find a teacher and say ‘I am thinking of doing X,
what did ‘they’ do for that?’ but that is not the point. Of course your teacher could tell you a method but
that will not make a good investigation and we aren’t going to tell you so don’t ask.
You need to discuss you titles with your teacher AT THE EARLIEST OPPORTUNITY.
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Preliminary work
You MUST try it out as soon as you can. TRUST US on this point. It is not just enough to assume that you will
be able to get some results.
There is ABSOLUTELY NO SUBSTITUTE for getting the equipment out and trying it out. You can do that at
any time – just ask.
This work will seal the fate of your choice… you will either decide to go ahead or choose something
different.
If you have decided to go ahead then you need to do 3 things
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Collect an exercise book to use as your lab notebook
Plan what you will do in detail
Order equipment
Do a risk assessment
We will need to see that the above is complete before you can start. You need to get your equipment order
in well before you plan to start. Bear in mind that we have a limited number of some items like
oscilloscopes and signal generators. Talk to a teacher about what you need.
Doing your investigation
This is the fun part!
You need to make full use of all your lesson time. You may do work outside of lessons. You must NOT work
in the lab on your own without the knowledge of a member of staff.
Things to do EVERY DAY
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Write the date and record everything that you DID and THOUGHT in your lab notebook.
Don’t forget to consider/write down uncertainties in all the measurements that you make.
Draw graphs of any data that you collected.
Make a note of questions to ask your teacher about.
Things to do AT TH END OF THE FIRST WEEK
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Write a brief summary in your lab notebook of what you have found out
Discuss how far you have got with your teacher
Make a new plan for the final week
Things to do AT THE END OF THE SECOND WEEK
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Dismantle all your equipment and return it in a neat fashion to the prep room
Discuss with your teacher what to do with any apparatus that you have constructed
Make sure that your work area is clean
Make sure that you have all the information that you need to write up the draft. This includes the
PHYSICS of what happened. See your teacher if you are not sure.
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Writing it up
Remember the lessons you learned writing up your Research and Report.
If you have been writing up what you have been doing EVERY DAY in your notebook then writing this up will
be a breeze. The reverse is doubly true.
The structure of your reports is up to you but may be as follows
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An aim
A summary
A brief outline of the physics involved in explaining what is going on
A risk assessment.
An account of what you did, including all the preliminary work, blind alleys and wrong turns – do
NOT sanitise your work. A diary format works well but it is up to you.
A section that says how you dealt with uncertainties
An analysis of the results that will have graphs and their interpretation
A conclusion which reflects on the outcomes of the investigation in a critical way.
An appendix that has all your results tables
A bibliography if applicable
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Investigation Checklist
Write a clear aim that states the question, problem or situation that you are investigating.
Write a summary of 200 words or less that gives an overview of what you did.
Write down what you did, including all the blind alleys, things that didn't work etc. A diary format is
a very good way of writing up, as long as you kept a record of what you did each day.
Include a risk assessment - make it clear how you gave due regard to safety
Explain clearly the physics of what you were trying to do
Think about the precision of your results. How many decimal places should you use?
Include details of any observations that you made - photos are great also. Careful
observations/diagrams are as good as numerical data
Tables of data should go in an appendix at the back of your report and must NOT be included in the
text.
Graphs of the data should be integrated into the account, as should calculations based on your data
ALL numbers should be quoted with an uncertainty as shown in your practice investigation pack available on the web or through me. If you do calculations you should carry the uncertainties
through to give an uncertainty in the quantity that you have calculated - see me if you don't know
how to do this.
Explain how you dealt with uncertainties and the steps that you took improve the precision
THINK about the graphs that you plot, make sure that they are correctly labelled and always
comment on them.
All points on all graphs must have error bars on them
Identify and explain any discrepancies between results
Explain, using physics, what you have found out. How certain can you be of what you think?
Think critically about what you have done and comment on the limitations. Saying 'I didn't have
enough time' will not suffice.
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Dealing with uncertainties and errors
You, the experimenter, will go and measure some physical quantities numerically (using some piece of
equipment to do so). You make a measurement. The measurement is necessarily somewhat different than
the true value of the physical quantity.
First, we need to define some terms:
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Accuracy: This is the extent to which your measurement is in fact close to the true value. If you do not a
priori know the true value, then it may be difficult to determine to what extent your measurement is
accurate.
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Precision: This is the extent to which you can specify the exactness of a measurement. For example, to report
that the time is about 3 PM is less precise than to say the time is 3:02:45. Being more precise does not always
imply being more accurate.
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Statistical (Random) Uncertainty: This is a key idea. The statistical uncertainty of a measurement is the
uncertainty that reflects the fact that every time you make a measurement, you must, be necessity, measure
a slightly different quantity each time. The tendency for a measured value to "jump around" from
measurement to measurement is the statistical error.
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Systematic Uncertainty: This is uncertainty and error in your measurement caused by anything that is not
statistical uncertainty. This includes instrumental effects, not-taking things into account (will the change in
barometric air pressure impact this measurement?) and gross (stupid) errors.
Any measured quantity or calculated constant requires 3 items in order to specify it completely:
(1) a numerical value
(2) a unit
(3) an indication of the reliability of the ascribed value.
Item (3) means the uncertainty or systematic error. Note that the two words, 'uncertainty' and 'error' are
often interchangeable. Strictly 'uncertainty' is best used to represent a range which contains the true value,
perhaps with a statistical confidence, whereas 'error' is best used to cover measurement deficiencies such
as systematic differences (errors).
An example of a fully specified statement might be: acceleration = 13.4 ± 0.2 km s-1
Absolute, Relative and Percentage Uncertainties/Errors
Statement: time for object to fall = 14.32 ± 0.04 s
The 0.04 is referred to as the absolute (time) uncertainty in the measurement. The relative uncertainty is
simply calculated as
0.04 / 14.32 = 0.0028
The percentage uncertainty = relative uncertainty x 100%
= 0.28%
So we can re-express the statement as:
time to fall = 14.32 s ± 0.3%
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Quoting Uncertainties
The uncertainty must be quoted to the same number of decimal digits as the value. e.g. 14.32 ± 0.04 and
not 14.32 ± 0.041
Knowing the uncertainty in a quantity immediately reveals the number of significant digits its value should
contain
e.g.
9.77
±
0.01
m
but
not
9.7742
±
0.01
m
since the uncertainty of ± 0.01m clearly indicates that the third significant figure is uncertain and thus there
is no point in writing down the 4th, 5th, etc.
Types of Uncertainties and Errors
Uncertainties are mainly of two types, systematic and random. There does exist a third type, blunders, but
they must be discarded when correctly recognised.
Systematic errors
Often these are the most difficult to deal with since you may not even be aware of their existence. They
cause a series of measurements to be always too high or too low rather than randomly scattered about the
true value; e.g. a shrunken ruler will always give length measurements which are too high.
Systematic errors must be carefully watched for and if possible eliminated or turned into random
uncertainties; e.g. in measuring a temperature difference, exchange the two thermometers and take a
second reading thereby eliminating zero errors.
Random Uncertainties
These may result either from the random varieties (often referred to as fluctuations) in the measured
quantity itself (e.g. the emission of alpha, beta or gamma rays from a radioactive source or from the
variations in measuring instruments and/or the experimenter. This simply means that repeated
measurements are unlikely to give precisely the same value each time. Rather a spread of values will be
obtained and it is from this spread or scatter that the uncertainty in the measured quantity is best
determined. You can turn this argument around and state that the best way of accurately determining the
uncertainty in any measured quantity is by repeating the measurement many times.
The next two sections, however, will consider situations in which a detailed treatment of measurement
scatter is not relevant.
Non-random Measurements
If you make a series of measurements and they all have the same value (see previous section) this indicates
that the instrument used for the measurement was possibly not sufficiently sensitive for the use intended
and you might then consider whether your choice is appropriate.
This does not mean, however, that there is no uncertainty in the measurements.
Example:
Using a vernier the following measurements were made of the diameter at different points along a
brass rod; 1.42 cm, 1.42 cm, 1.42 cm, 1.42 cm, 1.42 cm. Clearly any variations in diameter are too
small for the vernier to detect. This does not mean that there is no uncertainty in the result, but rather
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that it is not greater than half the smallest division that the vernier can measure, viz. 1/2 x 0.01 cm =
0.005 cm.
If the length had been greater than 1.42 cm the venier would have read it as 1.43 cm; if it had been
less than 1.415 the reading would have been 1.41 cm.
The result of this measurement is, therefore, written as 1.42 ± 0.005 cm
Limited Sampling
On many occasions you will not be in a position to repeat a measurement many times. For example,
recording the temperature of a cooling body; you measure single temperatures at specified times. Here you
must use your own judgement in determining how accurately the temperatures were measured. Under
ideal conditions the uncertainty is likely to be ± 1/2 of the smallest divisions of the instrument used. Note,
however, this is likely to be the minimum uncertainty and that systematic or instrument errors, may be
somewhat higher.
It is good practice to examine the manufacturers specifications for the instruments you use.
Time restrictions limit you to only a few, say 3 or 4 repeated measurements
Example:
Four length measurements of a rod were recorded as : 0.041, 0.044, 0.044 and 0.045 m. There are
two alternative approaches in calculating the uncertainty.
(a) Take the uncertainty as half the difference between the highest and lowest readings
= ± (0.045 - 0.042)/2 = ± 0.002 m.
(b) Calculate the average deviation for the four readings
For the above example this is ± 0.001 m which is half the value calculated in (a). The disadvantage
of this method is that calculating the spread in small samples using average deviations (or standard
deviations) is extremely dubious.
Manipulation of Independent Uncertainties
You will often have to calculate a quantity that depends on a number of measurements you have made,
each having some uncertainty. You should do this by taking LOTS of repeat measurements then draw dot
plots or histograms to see the range of your measurements about the mean. Half of this range is your
spread and represents your ± uncertainty
Error bars on graphs
You must account for the uncertainties in your measured points by representing these uncertainties as
error bars on your graphs. In nearly every experiment, you are varying some quantity, X, and the measuring
the impact on some quantity, Y. Measure the uncertainties in X and Y. Then plot Y vs. X with bars on Y and X
to show how uncertain the measurement was (see graph below). This is what a physicist means by error
bars. A graph without error bars is just plain wrong. Sometimes the size of the bar is very small - that's ok.
Once you have plotted the points, do a fit to some function (usually a line) that describes the physics you
expect, or just see what line you get. Remember that if you ask for a polynomial, you will get one. The
trendline is not 'it', it is not the point of the exercise.
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Once you have this you need to address the following question: is the best fit a good fit. In other words,
does the model fit the data to within the uncertainties prescribed by the error bars. This is the critical
question for the experimental physicist. Your goal is not to measure a number. Your goal is not even to
measure the "right" number. Really, your goal is to determine if the physical model is supported by the
data.
In my opinion, if you take this notion to heart, you will understand the soul of experimental physics. To do
this you must numerically answer the question: "Does the data fit the model to within the uncertainties on
the measurements?"
Sometimes, you may not know what it is supposed to do and what kind of line the physics would suggest.
In that case you are looking for a relationship between two quantities and to work out what that is you
have to find something to plot that gives you a straight line, e.g. y against x2. If you get a straight line, that
is the holy grail of physics - you can say that y is proportional to x2 - you have discovered a law that governs
those two quantities. Your next task is to work out WHY is should be x2 and not x3 or 1/x.
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Markscheme
List of titles
Absorption of radioactive emissions
• Acoustic properties of doubleglazing

Protection for postage parcels
• Resolution of the human eye
• Adhesive properties of blutak
• Resonance in wine glasses
• Aerofoil lift
• Bicycle brakes
• Resonant frequency of tower
blocks
• Bifilar pendulums
• Rising bubbles in fluids
• Bounce height of (squash) balls
• Ski jumps
• Compound pendulum
• Sliding friction
• Conduction in flames
• Solar cells
• Craters
• Sparks between electrodes
• Damping effects on SHM
• Stability of high-sided vehicles in
cross-winds
• Efficiency of the d.c.motor
• Efficiency of transformers
• Strength of chocolate
• Flight of shuttlecocks
• Structural properties of a daffodil
stem
• Fluid flow
• Tea diffusion
• Frictional effects of bowling shoes
• Thickness of soap bubbles
• Investigating sails
• Torsional pendulum
• Keels on boats
• Trebuchet
• Light absorption by liquids
• Vibrating strings
• Loudspeakers
• Viscosity of sugar solutions
• Magnetic braking / suspension
• Vortices in fluids
• Parachutes
• Water rockets
• Parallel plate capacitors
• Windmills
• Projectiles
THIS LIST IS NOT COMPULSORY – INDEED WE DO NOT HAVE
SOME OF THE EQUIPMENT. IT IS DESIGNED TO GIVE YOU A
FLAVOUR OF POSSIBLE TOPICS FOR YOUR INVESTIGATION
Example Piece of Work
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