By Jim Breithaupt

Jim Breithaupt taught for over 30 years in UK state schools and colleges. He is the author of many textbooks, including a number of highly regarded textbooks for international specifications including Essential Physics for Cambridge IGCSE® and Complete Physics for Cambridge International AS & A Level, Physics for OxfordAQA International GCSE and for OxfordAQA International AS & A Level. He has also written textbooks for AQA’s UK and Oxford International GCSE, AS & A Level Physics examinations. He is passionate about helping students in their learning, and supporting them to prepare for their exams.

Students moving on from Lower Secondary to IGCSE® Physics will meet a wide range of new concepts in their physics classes and they will carry out practical experiments in small groups to develop their knowledge and understanding of the subject. The syllabus matching grid on pp vi – ix (in Cambridge IGCSE® & O Level Essential Physics: Student Book) shows how the topics in student book cover the knowledge, skills and understanding students needed for their IGCSE® examination. Each of the 16 chapters in the book is set out clearly in double page ‘topic’ spreads which are mostly in the same order as in the syllabus. In each topic spread, essential knowledge, explanations and practical work are structured in short paragraphs. Students will start practical work at an early stage in the course and they will continue with practical work throughout their course. This blog post explores IGCSE® Physics practical work and how it is assessed.

Practical work is an essential feature of physics. Through practical work, students become aware that scientists learn about the natural world by carrying out experiments to test their ideas and to develop their knowledge and understanding. As well as encouraging enthusiasm for physics, the practical activities in the student book are  designed to help students

• understand the key concepts and describe the essential facts in each topic
• build up and assimilate the practical and mathematical skills in each topic
• prepare for the end-of-course  examinations including  practical assessment tests

In their practical work, students should appreciate that they are learning to follow the well-established scientific method, namely

• planning an investigation or experiment, starting with a question about some initial observations followed by a  prediction then a hypothesis backed up by scientific reasoning
• gathering  data through making careful observations and accurate measurements of  relevant quantities
• analysing their data to look for relationships between variable quantities
• evaluating their results in terms of accuracy and reliability to reach valid conclusions
• using their results and conclusions to make theories that explain their observations and can be tested further
• publishing their work so other scientists can assess and verify all aspects of their work (or in the case of students, writing an account of their work for assessment purposes!)

Practical assessment in the IGCSE® physics course is by means of either the ‘Practical Test’ (paper 5) in the laboratory or the ‘Alternative to Practical’ written paper (paper 6). Both forms of practical assessment

• require the same experimental skills to be developed and learned
• require an understanding of the same experimental contexts
• test the same assessment objective, AO3

Teachers and students should note in the practical assessment papers 5 and 6, students are asked questions using the specified experimental contexts listed in Table 1 below. There are four questions on each practical paper. In both papers:

• Questions 1-3 test the same skills in the same contexts  in the same way apart from ‘gathering data’ skills which are tested  in a different way in each paper
  1. In Paper 5, students use the instructions and apparatus provided to obtain a set of measurements
  2. In Paper 6, for the same number of marks, the same skills are tested ‘on paper’, for example candidates are asked to read a copy of an instrument scale or to complete a diagram or to answer a short question,for example about safety

• Question 4 is common to both papers and asks candidates to write a plan of an investigation. A typical question would provide an outline of an investigation in an unfamiliar context and a plan format (eg identify relevant factors and a key variable, what additional apparatus is needed, what to measure and how, how to obtain reliable results, what graph to plot and how to use the graph to analyse the results and to evaluate the investigation).

Table 1 lists the experimental contexts and topic references to the relevant practical activities in the student book. Further practical activities in these contexts are described in the accompanying Cambridge IGCSE® & O Level Physics: Exam Success Practical Workbook.

Context	Topic reference
Measurement of physical quantities such as	length	1.1, 2.2, 9.3
volume	1.1, 2.2
force	2.1, 2.4
Measurement of	small distances	1.1
short intervals of time	1.1, 1.3, 2.4, 9.3
Determining a derived quantity such as	the extension per unit load for a spring	2.3
the acceleration of an object	1.5, 2.4
the value of a known resistance	12.3
Testing and identifying the relationship	between two variables such as between the potential difference across a wire and its length	12.4
Comparing measured quantities	such as angles of reflection	7.3, 8.1,
Comparing derived quantities	such as density	2.2
Cooling and heating	measurement of temperature	6.3, 6.4, 6.5, 6.7
Experiments using	springs	2.3, 2.5
balances	2.1/2.2
Timing measurements	motion	1.3, 7.1
oscillations	1.1, 7.1
Electric circuits	the connection and reconnection of these circuits	13.2, 13.3, 13.4
the measurement of current	12.3, 12.4 ,13.3, 13.3
the measurement of potential difference	12.3, 12.4, 13.4,13.5
Optics experiments using equipment such as	optics pins	8.1
mirrors	8.1
prisms	8.8
lenses	8.5, 8.6
glass or Perspex blocks (both rectangular and semi-circular) including the use of transparent, translucent and opaque substances to investigate the transmission of light	8.3, 8.4
Procedures using simple apparatus	in situations where the method may not be familiar to the candidate.

The experimental skills to be assessed in Papers 5 and 6 are in five broad areas as listed below.

• Safety (S) : Demonstrate knowledge of how to select and safely use techniques, apparatus and materials (including following a sequence of instructions where appropriate)

• Planning (P) : Plan experiments and investigations

• Observations (O) : Make and record observations, measurements and estimates

• Analysis (A) : Interpret and evaluate experimental observations and data

• Evaluation (E) : Evaluate methods and suggest possible improvements

The specific skills  in each experimental skill area are described in pp 42-3 of  the syllabus document. By carrying out the practical activities in the student book, students should be able to build up and master all the required experimental skills. For example, the following notes illustrate how experimental skills can be introduced gradually and reinforced later.

Topic 1.1 Making measurements: students practice how to make accurate measurements of lengths, time intervals and volume measurements.

Skills covered:

• use common techniques and apparatus
• take readings from apparatus (analogue and digital)
• take readings with appropriate precision, reading to the nearest half-scale division
• correct for zero errors

The skills above can be practised again for use in later practical activities, for example as highlighted below in 1.2 Measuring speed and in 2.2 Density.

Topic 1.2  Measuring speed: students follow instructions to set up the arrangement safely, plan what to measure and how to use a stopwatch and metre rule to make the measurements accurately. Then they record their measurements and use them to calculate a derived quantity, namely speed.

Skills covered:

• use common techniques and apparatus
• select the most appropriate apparatus or method for the task and justify the choice made
• describe and explain hazards and identify safety precautions
• take readings from apparatus (analogue and digital)
• take readings with appropriate precision, reading to the nearest half-scale division
• correct for zero errors
• take sufficient measurements to be reliable
• process data, including for use in further calculations
• repeat measurements where appropriate
• present data graphically, including the use of best-fit lines
• analyse and interpret observations and data, including data presented graphically
• suggest possible improvements to the apparatus, experimental arrangements, methods or techniques

Topic 2.2 Density measurements:

• use common techniques, apparatus and materials
• select the most appropriate apparatus or method for the task and justify the choice made
• describe and explain hazards and identify safety precautions
• take readings from apparatus (analogue and digital)
• take readings with appropriate precision, reading to the nearest half-scale division
• correct for zero errors
• take sufficient observations or measurements to be reliable
• process data, including for use in further calculations using a calculator as appropriate

Safety Matters

Responsibility for safety matters rests with individual schools and colleges. Teachers should make sure that they do not contravene any school, education authority or government safety regulations. Science teachers must ensure their students are fully aware of safety when undertaking practical work and safety must take precedence over all other aspects of any science activity. Teachers should undertake a risk assessment before any activity is carried out and all necessary information and equipment should be supplied to students.

Note there are two types of eye protection: safety spectacles and safety goggles. Although both types should be impact-resistant, only safety-goggles are splash-proof.  Safety goggles should be worn whenever corrosive or toxic liquids are used and whenever an elastic material, spring or wire is stretched.

Practical Language

In the practical assessment papers, students are expected to be familiar with the measurement terms below as described on p43 of the IGCSE® Physics syllabus. To ensure they become familiar with these terms , they should be encouraged in their practical work throughout the course to use the syllabus terminology correctly and consistently.

accuracy
anomaly
dependent variable
independent variable
measurement error
precision
range
repeatability
reproducibility
true value
validity of experimental design

Students should also know that several repeat readings should be taken whenever possible to identify measurement errors which may be random or systematic. If repeat readings are the same, a more sensitive instrument could be used if possible.  

A random error causes repeat readings to differ. To minimise random errors, the mean value of the readings should be calculated after eliminating any reading that is an ‘outlier’ (ie. much further away from the other readings).  

A systematic error is present if the mean value differs from the true value. An example of a systematic error is a balance that is not set at zero correctly so all the readings consistently differ from the true value.  

The uncertainty in a spread of repeat readings can be estimated  by halving the range of the readings (ie half the difference between the maximum and minimum values after eliminating any outliers). By estimating the uncertainty of a set of readings as a percentage  of the mean value, the experimental accuracy of the mean value can be estimated and compared with the 10% upper limit referred to on p42 of the syllabus. In addition, the percentage uncertainty of different measured quantities in an experiment can be determined and used to identify possible improvements.  

In experiments where measurements cannot be repeated, such as when a thermometer is used to measure a temperature change, the least measureable change in the scale reading should be used as the uncertainty in the reading. For example, in a heating experiment, if the thermometer can be read to an accuracy of + 0.5 ^oC and the initial and final readings are 21.0 + 0.5^oC  and 35.5+ 0.5^oC, the temperature change is 14.5 + 1.0^oC . Note the uncertainty in the temperature change is + 1.0^oC because each of the two readings has an uncertainty of + 0.5 ^oC.

Explore IGCSE® Science resources by visiting the Cambridge IGCSE® & O Level Essential Science webpage and Cambridge IGCSE® & O Level Complete Science webpage, where you can find out more about the resources available, explore sample pages and request digital inspection copies.