Experimental work

Experimental work in Physics
Since the very basis of much of the study of Physics is by experiment it is important to know how to
carry experiments properly and how to present your results in the correct way. Very little faith can be
put in a theory if it can never be backed up by an experiment. They are of two main types:(a) standard investigations that are designed to prove accepted quantities or laws
(b) "open ended" experiments which are designed to investigate previously "unknown" areas of the
subject where there may be no previously recorded answers
Possible open ended experimental investigations
1. Energy in a balloon
2. Drag on small boats – use a piece of
3. Energy in a light bulb – LDR etc. – colour
4. Extension of the wire experiment – surface
5. Cars and carpet – braking experiments
6. Defects of a lens - astigmatism
7. Mixing water and methanol
8. Stretching a rubber band – heat effects
9. Expansion of a loaded rubber band when it
is heated
10. The propeller and drag
11. Strength of plants – bending in the wind
12. Resonance in buildings – earthquake
13. Mechanical resonance
14. The bifilar suspension
15. Growth of current in a light bulb
16. Absorption of light by glass
17. Waves on a stretched spring
18. Potential on a Van der Graaff – paper
19. Diffraction and resolution
20. Oscillation of tapes in an airflow
21. Falling magnet
22. Singing tube
23. Attractive forces in electromagnets
24. Fatigue in aluminium strips
25. Craters
26. Bouncing balls
Friction in curtain rails
How bubbles arise in liquids
Effect of polish on friction
The strength of adhesives
Vibrations in a soap film
Viscosity of liquids
Optical properties of treacle
Objects in an air stream
Standing waves on a vibrating wire hoop
The jumping ring
Penetration of nails into wood
Photochromic sunglasses
Bending of a beam
Electromagnetic clutch
Strengths of wet and dry tissues
Capillarity in sugar cubes
Thrust of model aircraft propellers
Transformer efficiency
Transmission of light through glass and
46. Conductivity of salt solution
47. The silt meter
48. The properties of a small water pump
49. Strength of a polythene bag
50. Forces in athletics
51. Damping and resonance
52. Reflection of microwaves from mesh of
different sizes
53. The efficiency of a small solar cell
54.Electromagnetic induction – separated coils
– thickness measurement
55. Air damping with a propellor
Some further comments on "open ended" experiments
In these experiments you cannot be sure what you will find - you won't find them written up in any
book so it is especially necessary that you plan them carefully.
Before starting ask yourself these questions and be able to answer them!
What am I going to measure or investigate?
What apparatus will I need and is it available?
How much time will I need for the investigation?
Will the readings be taken manually or automatically?
Are there any safety considerations that I should think about?
Do I need a control experiment?
Are my aims realistic?
What is my overall plan of action?
How will I present my results?
Suggested procedure for practical work
You should treat all your experiments carefully, no matter how simple they appear to be. Although it
is unlikely that you will stumble on a new law of physics during your a level course there is always a
chance and careful experimental work just opens up that possibility! A good experimental technique
gained at this stage could be of immense use later on.
When embarking on an experiment try and follow something close to the following suggestions:
1. Read all the instructions carefully before starting your practical work
2. Check that you have all the apparatus that you need and that you know how to use it. This is
especially true of meters and power supplies - ask for help if you are not sure which output or range
to use before switching on.
3. Plan your work before doing anything, that includes the setting up of the apparatus and the
presentation of results
4. Decide on the both the spread and the number of readings that you are going to take of the
various quantities.
5. Do not "set" your values to exact numbers - i.e. when making a series of measurements of the
period of swing of a pendulum take readings at roughly 5 cm intervals - do not try to adjust the length
to exact multiples, it will be very difficult and you are likely to measure inaccurately
6. Always repeat your readings if there is time and certainly check any reading that is to become a
"base" value used in many later parts of the experiment. Do not rush your work!
7. All results should be quoted to a sensible degree of accuracy and this accuracy recorded. Don't
claim an unreasonable degree of accuracy. Although a stop clock may show times to within 0.01 s
you may only be able to judge when to press it to +/- 0.1 s and it this that should be quoted as an
8. If you are asked for the gradient of a line in a practical question it is likely that the line is a straight
one, but if the slope at a specified point is asked for then the line will probably be a curve.
9. Include a comment of all errors and difficulties and how you overcame them or suggestions for
their solution.
10. A full and complete conclusion should appear at the end of each experimental account.
Remember that experiments without a mathematical answer are just as important as those that do
have a numerical result and a conclusion is still needed.
Tables of results
When writing up your practical work it is essential that tables of results are presented properly. They
 Be fully ruled out using a ruler
 Contain the correct information at the top of each column
 Contain only figures in the actual measurement and calculation section
 Contain the quantity at the top of each column
 Contain the correct units at the top of each column
 Contain an estimate of the accuracy of measured quantities at the top of each column
An example of part of such a table is set out below:
Length (L)
(+/- 0.0005 m)
Time for ten oscillations
(+/- 0.1 s)
Time for one oscillation
(+/- 0.01 s)
Drawing a graph
When drawing graphs the following points should be remembered:
1. The graph should fill the page if possible
2. It should have a sensible scale (e.g. 5 units matching five squares etc.)
3. The scale should be labelled with the quantity, symbol and units
4. The points should be clearly plotted, either as a small cross or a dot with a circle round it
5. The graph should be given a title
6. The line should always be the best fit curve (maybe a straight line) unless you are specifically requested
7. At least eight points should be plotted for a straight line graph and ten for curve
8. The gradient should be taken over as large a section of the graph as possible
Correct title given
Axis labelled
Points plotted correctly and clearly
Best fit curve
Figure 1
Gradient calculated
Anomalous point
recognized and
Axis labelled