A-level Physics - The Key Notes

Key Notes for A level Physics

Formulae

In Physics exams these days, there is an expectation that students will be provided with a formula sheet (although this is changing at GCSE!). This would appear to lighten the load on students (because they do not need to remember formulae) but it can mean that the teacher feels there is less need to focus on teaching the formulae.

Here are the drawbacks:

Like the phone numbers in their smartphones, students assume that they don t need to remember formula, so they pay less attention to understanding them

The formula sheet just gives a formula but gives no context not even the meanings of the symbols (or the units of quantities). Activities: 1. Get students to annotate their formulae with the meaning or symbols, including units, and the context of their use (eg. to work out the resistance of a wire from its resistivity). 2. Actually get students to learn formulae for each topic as you teach the topic and test them the formula sheet should be regarded as a safety net. Students may resist this, but try to persuade them that learning a formula speeds up access time and aids understanding.

Rearranging formulae should not be a problem, but it is. Students with poor algebra skills will struggle. Even high achievers make careless mistakes. Activity: Teach techniques for rearrangement explicitly and do regular speed test on rearranging formula using the formula they actually need and getting them to make each quantity the subject, will help them to recognise correct/ incorrect rearrangements.

Common errors with evaluating formula: here are some classics using diameter instead or radius in area/volume calculations, using Celsius instead of Kelvin in thermodynamic problems, careless use of brackets.

Computational skills are variable amongst students. Very few students know how to break calculations down step by step (unless forced to) everything goes into the calculator. The two issues are speed and accuracy. The biggest issues are : are with use of brackets and checking the sense of answers. Also students should be encouraged to break calculations into steps the justifications for this are that you are less likely to make errors and that if you do, then the examiner can give some credit for the working out. Activity: Give regular speed and accuracy test (timed). Expect high speed and perfect accuracy.

The most common cause of mark-loss in problems which involve formulae is the dreaded POT this is some common that often examiners will ignore it! POT means power of ten and usually indicate that the student has not taken account of units or has been sloppy about the use of standard form. There should be zero tolerance with regard to units students must use the correct units throughout and record units throughout. The problem arises partly because weaker students don t get units and so ignore them, so that stronger students pick up these bad habits. Always penalise incorrect use of units and incorrect POT.

Biggest mistake with units (even for high achieving students) trying to convert to SI units at the end of a problem instead of the start (Particular serious with area and volume.

Laying out of work is a major issue with students weak students are very poor at this but even some very able students, who get the right answers, lay out their work poorly. Students are reluctant to layout their work carefully the need to be trained to do so, it is not intuitive. The reasons for laying out work clearly are so that the examiner knows what you are doing and can award marks accordingly so that the student themselves know what they are doing and can follow their own train of reasoning. One of the biggest obstacles to effective layout technique is the use of calculators- students literally try to do the whole problem on a calculator and then write down the steps retrospectively. Although some students can cope with this it should be declared illegal! Activity: Give students a set of problems to solve with the following rules: working out should be on rough paper and then written out neatly, all steps of the processing should be recorded in sequence and the calculator should NOT be used until the final step. In this exercise, speed is not of the essence, especially in the early stages when students are developing the skill.

Communication skills

Written communication skills are a major problem with Physics students. This is partly because the type of students who choose Physics are reluctant readers and writers. The exams are examined through written communication, but students often have the view that if they know what the mean then the examiner will give them the marks! Students who can express themselves orally cannot necessarily express themselves in writing so written communication needs to be treated as a separate skill. This is why the use of classroom activities like discussions are not guaranteed to be effective.

Since recall of definitions is generally not tested these days, the tendency is not to expect students to learn by rote. The effect however is that students come up with improvised answers in exams which gain no marks. The problem is that examiners want to see the technical language which are indicated on the mark scheme. Students are not to guaranteed to come up with this language if hey haven t learned these terms in the first place. One good way to approach this is as follows:

Get students to learn definitions and key phrases by heart (not just single words but phrases). At this stage they will not fully understand what they are learning, but this is to be expected.

Get students to deconstruct their definitions and explain them. So, as they are learning to understand concepts they already have the necessary terms.

Example: it is customary to teach Newton s laws by expressing them in simple every day terms, but in the exam students will come unstuck and fail to get any marks. Better to start off with the formal statements and then get students to develop their own interpretations (in their own words) whilst retaining the formal definition for use in the exam.

If you run activities involving discussion of complex concepts, students MUST write down the descri ptions and explanations at the end of the activity to ensure they develop the necessary written communication skills.

Practical skills

The important skills developed by carrying out practicals are :

Recognition and use of equipment

Planning skills particularly in relation to reducing uncertainty (they find this concept really difficult)

Graphical analysis

Evaluation of the experimental results again the concept of uncertainty comes up again.

Taking them one by one:

Recognition and use of equipment

There is a disconnect between doing an experiment and writing about it. In the exam they need to name the equipment used whereas in the practical session they can carry out the measurement without even knowing the names of things (or their spellings). Likewise in the exam they need to describe the process of using the equipment, whereas in the practical session they may just follow a series of steps without much thought, and possible little understanding. Finally, most practicals are carried out in small groups and often students re just hangers-on who really don t know what s going on. When students have to do practicals by themselves, their lack of understanding comes as a shock.

Advice:

There must be a written method produced by each student as part of the practical activity not just copied from the activity sheet or from another student but written from memory

Take all opportunities to get students to work by themselves a good source for tis are legacy practical exams which use simple equipment.

Planning skills particularly in relation to reducing uncertainty (they find this concept really difficult).

Time for practical work is limited so there is a tendency to rush into a practical session to get the experiment completed on time. Which means limited time to actually plan an experiment. It is worth having whole sessions on planning without the plan being enacted. Students are set a task of planning an experiment with the equipment available, a whole session on this. They must write the plan. If time is not available to implement the plan, this doesn t matter a lot of experiments involve repetitive data recording which do not develop much in the way of skills and of little use for exam preparation.

The concept of Uncertainty is crucial. It is worth raising this to a level of a law of physics which must always be obeyed. Students find the subject very dry and don t recognise the importance. It is similar to the attitudes to units and to significant figures. Make sure that Uncertainty estimation and calculation takes place in every experiment. I get students to calculate Total Uncertainty and compare with Percentage Difference from expected value if it is larger then they have done well!

Evaluation of the experimental results again the concept of uncertainty comes up again.

In terms of evaluation, Uncertainty is crucial in identifying the flaws in the experimental method and modifications required. The key idea is that the measurement/ quantity with the largest Percentage Uncertainty is the one that needs to be addressed. Measurements with negligible uncertainty do not need to be refined.

A more detailed skill which students find challenging is to identify how uncertainty affects the final value. For example, if there is a systematic error (a zero error) how will this have affected the values obtained. This is a subtle logical exercise which needs to be worked through step by step. It is quite confusing and students need to practice this skill.

Graphical analysis

Graphs questions in exams are potential sources of easy marks if they are answered correctly.

Students need to know the precise rules about plotting points and drawing lines of best fit and worst fit. The practical handbook is a must.

Origins are sometimes a problem there is a judgement about drawing a line through the origin or not. The origin measurement, if it is actually measured has uncertainty as well, so it needs an error bar and should be treated like any other point. So if the line of best fit missing the origin, this is OK and indicates systematic error. False origins are fine, but they need to be aware of how this affects the intercept calculation if needed.

Make sure they use large triangles to calculate the gradient (they pick up the small triangle approach from Maths)

Correct labelling of axes is vital including units and scaling factors. Incorrect gradient values will result unless these rules are followed. Choice of scale is important never use intervals like 3 or 7. Also the scale should be chosen so that graph fills over half the page .

Show students the mark-scheme these are not just subjective considerations, the examiner is looking at these qualities.

Exam Technique

Students need to develop their own technique what is best for them.

Here are some useful guidelines:

MCQs. The first rule is to recognise that these carry few marks and eat up time. They are often at the start of the paper, but you are advised NOT to tackle them first. Suggest you leave say 30 mins at the end for the MCQs. Lots of practice is needed on these, both to develop technique and to get to recognise standard questions. There are different techniques such as eliminating the clearly incorrect responses or working out the answer then matching to each choice the point is that different style questions need different optimal approaches.

Structured questions : these need structured answers. Students need to use the mark schemes to show them how to lay out the answers. It is vital that the understand the marking methodology

o marks are given for individual steps, and these steps need to be transparent to the marker, which means laid out in a logical order. Don t skip steps (such as substitution into formulae). The skipped steps may have been worth marks.

o the concept of ecf which means that you can still get marks further down the line if you make earlier mistakes don t give up. Remember, the actual numbers in answers get few marks, it is the process that gets the marks.

o if you get wrong answers, markers will look for correct working, even in cancelled work so leave cancelled work readable

o Keep your answer in the answer box - it may be missed.

o Examiners are only human if they can t see the correct answer they will not award a mark.

o Students need to be aware from day one of the course that illegible work can never achieve marks my handwriting has always been bad is not an acceptable excuse.

o A simple strategy is to look at the mark allocation for a question and match it: it its 3 marks you need at least 3 key ideas.

o Another strategy is to focus on easy marks (usually earlier parts of questions) rather than get involved in solving the difficult final question parts.

o If you are literally running out of time, make sure you get a few key words into empty boxes they may just get you some extra marks.

o Students need to understand the action words: probably the biggest confusion is between Describe and Explain. Explain suggests the application of a scientific principle.

o Reading (misreading) of the question is cited as the major course of mark-loss (even for high achievers). This is a result of exam stress, we all do it. Techniques for reducing this: reading the question twice, highlighting keywords, aiming to finish early and proof read all your answers against the questions. Reading the whole of a structured question before starting on it is recommended but needs a lot of willpower. However, all of this advice depends on one factor Time. If you are well-prepared for an exam then you will answer questions more quickly, and then you will have time for quality control .

o So the key to all of this is good revision strategies.

Revision strategies

As with exam strategies, each student needs to develop a strategy which works for them.

It is easier to list ineffective strategies which occur commonly:

Cramming in the last week or two before the exam

Staying up all night before an exam

Reading (passively)through the text book or revision books

Working through exam papers but not reading the textbook

So the revision process needs to be

An active process, answering questions or making notes

Exam-focussed, practising exam style questions under exam conditions

An extended process, not a last minute rush