Required Practical Assessments

Introduction

You will be required to submit 12 required practicals in your A-level course.  6 of these  will be during the first year (AS) and 6 of these will be in the second year (A2).  You will need to have a portfolio of this work which will need to be submitted to the Board for your practical endorsement.  In most centres, your tutors will keep your work in the office.  If that is not the case, you are responsible for its safe keeping.  If you transfer from one centre to another centre for the second year (for example, your parents get a new job and need to move house), your new centre will ask your old centre for your practical work.  They should forward it, but it does not always happen.  Then you will need to do it again.  Yes. it's tedious.

 

Required practical experiments are done throughout the year during routine practical work.  They are NOT carried out in the context of an examination.  However there will be questions in the written papers at the end of the year that will refer to your required practical portfolio.  The data to be processed will be provided in the question, so you don't need to remember the data you collected.  You do need to know what you did with them.

 

The work will be graded as a Pass or a Fail at the end of the second year.    Your practical mark will be independent of your examination score, so it's possible (though rare) to get a Grade A*, but fail your practical assessment.

 

There is no separate practical component in the AS year.  Your work is carried across to the second year.  If you aren't continuing to the second year, you can ask your tutors for the work, and you can do what you like with it.

 

The general scheme of assessment is common across all the boards, but there may be differences in the detail.  The notes here are primarily for the AQA syllabus, but most of the time are relevant to other boards.  If there is a significant difference, it will be indicated. 

 

For students doing the SQA Higher and Advanced Higher Syllabuses, there is a different approach. 

 

Required Practicals

The required practicals for the AQA for the first year are as follows:

1. Investigation into the variation of the frequency of stationary waves on a string with length, tension and mass per unit length of the string.

2. Investigation of interference effects to include the Young’s slit experiment and interference by a diffraction grating.

3. Determination of g by a free-fall method.

4. Determination of the Young modulus by a simple method.

5. Determination of resistivity of a wire using a micrometer, ammeter and voltmeter.

6. Investigation of the emf and internal resistance of electric cells and batteries by measuring the variation of the terminal pd of the cell with current in it.

 

It is most likely that your tutor will give you commercially available worksheets to do the required practicals.  These will have been tested by their authors and others, before approval for publication.  These will have instructions and questions.

 

There is quite a lot in the induction notes about how to write practical reports.

 

Your tutor will assess these.  Tutors are trained by the examination boards, so that they are looking for specific things in their assessment.  The training ensures that, as far as possible, all centres mark assessment to the same standard.

 

Apparatus and Techniques

In doing the required practicals, your tutor will be looking for evidence that you have carried out the following:

 

Clearly you would not carry out all techniques at once. 

 

Question 1

Which of the Apparatus and Techniques statements above would be appropriate for an experiment to measure resistivity (Required Practical 5)?

Answer

 

Competencies

There are five competencies that you will need to demonstrate to pass your required practical assessments. 

1. Follow written procedures;

2. Apply investigative approaches and methods when using instruments and equipment;

3. Safely use a range of practical equipment and materials;

4. Make and record observations;

5. Research, reference and report.

 

Your tutor will observe how you carry out experimental work.  In reality, most Physics AS students will apply these competences as a matter of course.

 

1. Follow instructions

If you can follow instructions for a standard procedure, or a more complex procedure, you will pass.  The procedures will be more challenging as you progress through the course.  As a matter of course, it is assumed that you can work with others. 

 

A standard procedure might be to set up a circuit to measure voltage and current in a circuit.  A complex procedure would require a number of steps to set up the apparatus.  An example of this may be to measure the energy supplied by a heater and measurement of temperature of water, possibly with a data-logger.

 

Working with others means just that.  In many a job advert you will see the phrase, “…must be a good team player…”, which is management-speak for working in co-operation with others.  In a commercial aeroplane, the pilot flies the aircraft.  The co-pilot does not sit there for the ride.  He (or she) assists the pilot in the many checklists for the flight, tunes the communication and navigation radios, keeps track of the flight-plan, and generally reduces the work-load of the pilot.

 

It does not mean:

 

These men would say that they are working with others in this study in indolence. 

 

 

It means that each student takes responsibility for getting part of the experiment set up and data recorded.  You need to work co-operatively so that the task gets done quickly, and effectively.  While it’s most comfortable to do it with friends, you may find yourself having to work with someone you might not necessarily get on with socially.  Tough.  In life, you will have to work with people who might not be your “cup of tea”, or whom you positively cannot stand.

 

Groups that get right idea about working together get the work done quickly and effectively.

 

Question 2

Think about how well you work together with others.  How much time do you spend as a group discussing anything other than the task in hand?  Is there anything you can do to improve this?

Answer

 

Organisation

Parkinson’s Law, coined by Cyril Northcote Parkinson (1909 – 1993), tells us that:

Work expands so as to fill the time available for its completion.

 

In other words a lot of time can be wasted.  And this happens frequently in practical work.  One person (if that) does the work, while others watch.  The comments about working with others are relevant here as well.  The picture above (the study in indolence) is a result of poor organisation.

 

To avoid wasting time, and get the maximum benefit from practical work, you need to:

 

If one member of the group is not sure how to do the experiment, show him or her.  If a student are not sure of the physics, help him or her; peer teaching is very effective.

 

On completion of the practical work, each student should make its own copy of the results.  Then get on with doing the graph and answering the question.  Remember that the more you get done in class, the less you have to do for homework.

 

 

2. Apply investigative approaches and methods when using instruments and equipment

A generic worksheet that is published commercially may well give very general instructions, along the lines of "Use about a metre of resistance wire".  What kind of resistance wire?  What diameter?  How are you going to measure lengths to reduce uncertainty?

 

You may be given apparatus that varies from that in the worksheet.  The authors would have written their instructions in their normal style, using equipment that was available in their physics departments.  They may have specified a 30-ohm resistor in the worksheet.  Your department may have 10-ohm resistors.

 

So if you do a preliminary experiment to decide on appropriate ranges for meters, you are applying an investigative approach.  You may be given a resistance wire, of which you know nothing.  You can investigate it by measuring the diameter in three or more places with a micrometer.  As for the material, its resistivity will give you its identity when you compare your value for resistivity with the value given in a data sheet.  You will have successfully carried out an investigative approach to identify what the material is.

 

The preliminary experiment may help you to decide what interval to use for your independent variable, and what values of control variable you will use.

 

A more challenging task will be for you to devise your own experimental strategies to investigate one of the required practicals.  If you do that, get decent results, and write a report, you have certainly shown evidence for application of investigative approaches and methods when using instruments and equipment.

 

 

 

 

3. Safely use a range of practical equipment and materials

This competency concerns the choice and use of equipment for a procedure.  At AS level, you use standard laboratory equipment such as a digital multimeter and select the appropriate range.

 

 

In this picture, the 600 volt AC range has been chosen.  You can see that there are a lot of other ranges that can be chosen.  Other standard equipment includes:

Not very high-tech, but perfectly good for harvesting accurate data.

 

You need to do repeat readings where appropriate.  It is good practice to do this anyway.

 

It should go without saying that equipment is used properly in accordance with the instructions.  While most school laboratory equipment is well-made, it is not indestructible.  It is also remarkably, if not eye-wateringly, expensive.  And if you damage it through abuse, you may get a bill for it, as well as an interview with the Head of Physics, the Vice-Principal, or the Headmistress...

 

Question 3

You have a 15 volt DC power supply.  What range would you use to measure this voltage?

Answer

 

A more challenging instrument to use is an analogue meter.  A school analogue meter consists of a basic meter, to which you add components that are appropriate to the measurements.  These are:

 

And there is another factor you need to consider.  What is the value of the quantity you are going to measure?  If you are going to measure 20 mA, you will get nowhere if you use a 10 amp shunt.  And then which scale you use.  If you use the 10 V multiplier, you would use the "10 range", so that a reading of 4.6 gives a reading of 4.6 V.  If you have a 20 V multiplier, then a reading on of 4.6 on the 10 range would give 9.2 volts.

 

Question 4

You are using the 2 amp shunt.  The needle shows 7.2 on the "10 range".  What is the current?

Answer

 

Safety

No activity in college or work is so important that people should put themselves or others at risk.  The risks in a school physics laboratory are very low, but students still have a responsibility to look after their own safety and that of others.

Risks in physics experiments include:

 

Safety should always be considered before carrying out any experiment.  If equipment is faulty, it must be reported to the teacher.  It should go without saying that no action should be taken to compromise safety by abusing equipment or doing unauthorised experiments.

 

You should get into the habit of making your own risk assessment, even though your teacher will have carried out a risk assessment previously.  In this, you should consider:

 

As always this is not an exhaustive list.

 

Question 5

 Write a risk assessment for carrying out an experiment to investigate resistivity.

Answer

 

And when you have done the risk assessment, follow it.  You may want to use goggles.  You might decide on using a heat-proof mat, and so on.

 

Any shout of “ouch!” means that you are not working safely.

 

4. Make and record observations

When I first started teaching, it was the trendy idea that it didn't matter how the results were written down as long as they were the actual results that were obtained on the day.  The trouble with that approach is that what might make sense on the day will end up being absolutely meaningless a few days later.  (My lecture notes at university were like that.)

 

It is far more effective to write a prepared table.  The layout will be informed by not just the worksheet, but also any preliminary experiment you do.  Your results sheet should have:

The individual cells should be boxed in with pencil.

 

If you have to process data, provision should be made on the results table.  Do not use a second table to process the data.

 

Seldom are the rough results neat enough to go into the final report - mine certainly weren't.  I always encouraged my students to write their results "in smooth" in their report.  The advantage of this is that the table can be easily read and understood.  Be careful that you don't make any transcription errors.

 

I write at length about presentation HERE in the Induction Notes.

 

 

5. Research, reference and report

This competency requires you to research a method and/or expected results for one of your required practicals, instead of following a set of instructions given out by your tutor. 

 

You can do this using a text-book from your school or college library.  You could use a web site.  I got my students to research from at least two different sources.

 

You should write your findings in your own words, showing that you understand what your research is telling you.  Anyone can do a cut and paste from a website.  To do this and pass it off as your own work is plagiarism and can be considered to be malpractice.  When you actually do the practical, you could mention what changes you made in your method.  (For example:  "...I used 0.1 N loads instead of 1.0 N loads because the wire used had a much smaller diameter..."  In this way, you are demonstrating how your research informed the planning of your experiment.

 

You also need to consider what the expected results are and compare how your results matched up with the expected results.  For example, the expected Young Modulus for a material might be 2.0 × 1010 Pa, but your result might be 3.5 × 109 Pa.  Your result may be low because of the imperfections in the crystal structure of the test wire that result from drawing it through a die.  You could research the reasons for this on-line.  Give the reference.

 

You MUST put your references in a way that your reader can find the text easily.  For example, "Reference - Fullick textbook" is not referencing at all.  It doesn't give a title.  Fullick could have written any number of textbooks.  Which Fullick anyway? (Patrick Fullick is the author of a Physics textbook.  Anne Fullick writes a Chemistry textbook.)  The reader (your tutor) does has neither the time nor the inclination to read Fullick's textbook from cover to cover. 

 

To write this correctly, you should reference at least like this:

(1) Measuring the Young Modulus, Physics by Patrick Fullick, Chapter 2.2, pp 128 - 129 (Heinemann 1994).

(2) Measuring the Young Modulus, Phyics for You by Keith Johnson...

 

When referencing from a website, you must give the full url (uniform resource locator).  This can be copied and pasted from the url bar on your browser.  For example:

https://www.quora.com/Whats-the-difference-between-experimental-and-theoretical-value