Induction Tutorial 9 - Using ICT in Physics

 Contents

Computers are used widely in Physics, not only in research, but also teaching.  They initially came into teaching in schools and colleges about thirty years ago with the BBC microcomputer.  There may be some schools that still use them for data-logging.  Programs came on large floppy discs.  Operating them was simplicity itself.  A program was started by pressing SHIFT + BREAK.  There was a range of sensors and interface boxes that worked with the BBC.  Laughably crude nowadays, they were effective data loggers, although they printed out graphs on dot-matrix printers with tractor feeds.  (Ask your tutor - there is probably one hidden in a corner of the prep-room).

ICT should play a central role in much of your learning, regardless of what subject you are doing.  In this tutorial we will look at how you can use ICT enhance your studies.  However you should be aware that no computer can be a substitute for a teacher, and you still need to use the old-fashioned low-tech approach to study, such as:

• Writing notes;

• Using a text-book (very reliable, doesn't crash, and can be used anywhere);

• Hand-written assignments (setting out equations on a computer is time-consuming.  It can be done much faster by hand).

In the exam, you will still need to hand-write your answers.  Some people think that legible hand-writing is over-pedantic and old-fashioned.  Examiners and employers do not.  My own hand-writing is not the best in the world, but I try to make it legible.

Computers can be used for:

• Data-logging;

• Mathematical modelling;

• Research on the Internet;

• Animations to illustrate concepts.

We will look at each of these in turn.

Data-Logging

In a data-logging experiment, you will use:

• a sensor which detects some kind of change, e.g. temperature;

• a sensor unit which translates the output of the sensor into digital form.

• a data-logging unit.

The picture below shows a probe with the sensor unit that connects it to the data-logger.

The data-logger is shown below:

Other models are available, and will have a different layout.  This one has a screen that will display the data in a table or a graph.  There is a stylus that allows the user to change settings on a dialogue screen.  The screen is small, so fingers are too fat and clumsy!

There are four input channels which can be connected to different sensors of the same kind (e.g. 4 temperature probes) or of different kinds (e.g. voltmeter and ammeter).  Channel 1 and Channel 2 are also marked A and B.  This is to allow for light gate sensors in two different positions.  The picture shows a pair of light gates:

There are sensors for a whole range of applications:

• Voltage sensors, that are wired into a circuit just like a voltmeter;

• Current sensors, which are wired in like an ammeter;

• Temperature sensors that are used like a thermometer;

• Magnetic field sensors;

• Light level sensors;

• Position sensors.

The list goes on.  In biology, there are oxygen sensors.  In chemistry there are pH sensors.

The most obvious way of using a data-logger is to measure some variable (like voltage) against time.  The data-logger can be set to record every millisecond, or second, ten seconds...  This is called the sample rate.  This means that the time period for a recording can be from a fraction of a second up to several days.  There is much reduced uncertainty compared with a stopwatch (reaction time is about 1/3 second), and the instrument does the recording unsupervised, so you can get on with something else.

Time is, of course, not the only independent variable.

This apparatus shows a data-logging experiment in which the pressure of a fixed volume of gas is measured against the temperature.  The computer is set to measure the pressure for each increase of temperature of 1 oC.  In other experiments, the data of the independent variable can be put into the data-logger manually.

Drawbacks of Data-Loggers

There are some drawbacks to using data-logging in experiments:

• Data-loggers are not necessarily more precise or accurate than traditional techniques.  It all depends on the accuracy of the calibration of the instruments.

• The sensors can be affected by noise (spurious electrical signals) which makes the graphs harder to interpret.

• The equipment can take longer to set up.

• Some data-logging equipment can be difficult to use.  This leads to frustration for both the students and the tutor.

• Some data-loggers can only use time as the independent variable.

It is important that each student should have his/her own copy of the results from the computer.  It is not unknown for students to save their data on the laptop that is then stored away on the laptop trolley, and the students have no idea of which one they used.  Another common and depressing scenario is for a student to say to the tutor, "Ollie took the results.  He said he would e-mail them, but he never did..."

Examples of Data-Logger Experiments

You will do experiments like these throughout your course.  The precise instructions will vary.

The diagram below shows a typical experiment using light gates on a linear air track.

Light gate A is connected to input A on the data logger, and light gate B is connected to input B.  Various motion quantities can be be measured using the card and the light gates, for example:

• Speed;

• Velocity, where direction is included;

• Acceleration.

You can also use data-logging with light gates to measure the acceleration due to gravity.

This next example shows the circuit diagram to measure the charging up of a capacitor (which you will study in the A-level year).

Notice that the voltmeter and ammeter sensors are represented by their normal symbols, except the connections to the data-logger.  The data-logger has to be turned on at the same time as the switch S is closed.  Easier said than done.

The data are recorded by the data-logger.  They can be transferred to the computer, often as a .CSV file (Comma Separated Values), which can be read by the Excel spreadsheet program.  They can be used to produced a graph.  Here is the graph for a data-logging experiment.

The experiment below shows an experiment to measure a very brief change in voltage and current in an inductor, like an electric motor.  The symbol for an inductor is this:

The inductor has a value of 10 milliHenries (10 mH).

Don't worry about what an inductive component is or its units.  You may meet them in the A-level year, depending on the syllabus you are studying. The way the current and voltage behave is not on the syllabus, but it changes in a very rapid transient, which cannot be studied using a voltmeter and stopwatch.  The circuit is like this:

Notice that the voltmeter and ammeter sensors are represented by their normal symbols, except the connections to the data-logger.  The data-logger has to be turned on at the same time as the switch S is closed.  Easier said than done.

This graph shows the inductive rise in the input voltage of a motor from a data-logging experiment.

Notice how quickly the voltage rises to its maximum level, 12 V.  Also at time = 0, the voltage was at 4.4 V.  This is because the data-logger was not switched on at quite the right time.

On many of the pages of this website, you will see many sketch graphs.  They give a rough idea of the shape of a relationship.  They can be unsatisfactory, as drawing consistent curves freehand is not easy.  It's even harder with a mouse!  Consistent curves are essential if concepts such as phase are to be illustrated properly.  Excel Spreadsheets can produce much better graphs, and you will see these on various pages of this site.

Data-modelling is about using a formula with known values.  A formula is a function machine that processes one number with another to give an answer.  You can do it manually, of course, but it is remarkably tedious.  A spreadsheet does this in minutes.  This is not a tutorial on how to use Excel, which you will have done in ICT lessons.  If you are unsure, ask a classmate who is a dab-hand at Excel, or look up an on-line tutorial.

We care going to do a simple piece of data-modelling using voltage and current in a resistor.  We know that resistance is related to voltage and current by:

and that power is related to voltage and current by:

So let's look at the power dissipated by a 15 W resistor.

So open an Excel file and call it something meaningful, like Power.

In the headings of the table, list voltage, current, and power.  In a cell above this, put the value of the resistance.

You can change the value of the resistance and the spreadsheet will change everything.  So start at a voltage of 0, and go up in steps of 0.1 V, up to 10 V.  We have now defined the step.  This is shown below:

Pull the drag-handle downwards, and pull it down until you reach 10 V:

Now we make the first formula, as shown here:

To start a formula, we type in Cell 4 an equals sign (=).  The formula is =A4/F\$1.  The cell F1 contains the resistance, 15 ohms.  The dollar sign before the number keeps that cell locked.  Otherwise, when we pull the drag handle, the formula will pick up F2 which does not have any contents.  The next cell would return the answer to A5 ÷ 0, which would give an error, like this:

So pulling the drag handle gives us:

The data have all sorts of decimal places, which looks messy.  Select Column B.  We can adjust the number of significant figures displayed by using the Number drop-down menu:

Click at the bottom right, and you will see the dialogue box.

Select the Number data type, and select 3 decimal places, before clicking OK.  Note that whatever the number of decimal places are selected, the underlying data are not affected.  The data now look like this:

Now we can apply a formula for Column C which gives us the power.  Select C4 and type the = sign.  Then select A4, then type * (it is the multiplication operator in Excel) then select B4.  You should have:

=A4*B4

Drag the formula down Column C:

Format the number to 3 decimal places:

Now select Column A and then Column B with the CTRL key pressed.  Then go to the INSERT menu and select Scatter Chart.  (Don't select the Line Chart which does dot-to-dot.)  You will get the graph as an object in your data page:

You can move it by pressing the button, Move Chart Location.  It goes to a separate page.  You can then format the graph.  The pre-set format given by this button is the most useful:

This gives us:

The box, Series 1 can be selected and deleted.  Put a heading by selecting Chart Title and putting in an appropriate heading.  Then label the axes.  The vertical axis is Current / A, and the horizontal axis is Voltage / V

We now have our graph:

However it's not quite finished.  We want to show the grid lines.  We right-click on each axis to format the axis.  I cannot show the right-click dialogue box, but select show major grid lines, and then minor gridlines.  Do the same for the second axis.  This will give us:

And we can easily draw a graph of Power against Voltage:

Now let's look at what we can do if we square the current, since:

So we can make an extra column, D, headed Current^2 / A^2.  The notation is because Excel does not do superscript text.  The formula is =B4^2.  This will square the number in B4:

Excel does not allow us to reverse the axes easily.  So if we want Power against Current2, we need to copy the contents of column C into Column E.  In E4 we simply type: =C4.  Then drag down.  This allows us to plot this graph:

Once you have got the hang of this, the production of spreadsheet data models is not that hard.  If you have a complex formula, it is best to break it up into small bits, rather than applying the whole formula, which can easily go wrong.  The actual production of this model took me about 10 minutes, a much lower time that it took me to produce the notes.

The data produced by a data model are idealised, using a formula.  The data from an experiment may well be different, so do not produce neat graphs.  This is because of uncertainty in the experimental process.

More advanced software is used by physicists for more complex data-modelling.  Very sophisticated programs using complex equations and mathematical techniques can be used to model the behaviour of complex systems like multiple black holes.  Engineers use data modelling in the design of new aeroplanes.  They can test the model to destruction, without putting a pilot and others at risk.

That you are reading these notes is because you are using the internet.

The internet contains a whole library of useful information that you can use help you with your studies.  There is also a lot of absolute drivel.  Your tutor may recommend sites for you to visit, and there are links at the top of the page, if you are not viewing this page in whole page format.

If you are using the internet to do a project, you must give the URL for where you find material. If you are quoting, it must be obvious that you are, for example the material is in a different font, or in quotation marks.  You must reference the extract as instructed by your tutor (I usually insisted on a number in the text, and the link at the end under References).

Plagiarism is where you try to pass off others' work as your own.  At its crudest, the introductory paragraph is meaningless and littered with spelling and grammatical mistakes.  Then the prose suddenly becomes fluent, sometimes with concepts that are way beyond the level of the writer.  The final paragraph reverts to type.  You can expect very few marks from something like that.  A good number of institutions insist that students submit assignment in electronic form, and they are processed using anti-plagiarism software.  Institutions take a dim view of plagiarism.  If there is plagiarised material, you may well have to account for it with your tutor and/or the Head of Sixth Form.  A lenient view may be taken the first time, since you are considered to be doing it out of inexperience.  The second time may end up that you have to resubmit the work, and you are warned.  Multiple times may lead to a disciplinary.

These can be found on many websites, and there are many programs available with which you can do your own.  I am not skilled in the use of animation software.  I have used Paintshop Pro 7 which includes Animationshop.  Both are now quite old programs.  My own animations are crude, although illustrate the ideas.  Others of my students, who more skilled than I, have produced some very professional looking animations.  I have two on this written by Stephen Lucas.

Other programs that can be used include Shockwave, Flash, and Photoshop.  The Shockwave and and Flash files need a player.  You can use the animated objects in PowerPoint as well.  Most animations on the internet are either .MPEG or .GIF files.

Production of good animations is a skilful process that takes a long time.  However, if you are skilled in ICT, you will find it very satisfying, and your skills would be sought after by many in the industry.