NATIONAL QUALIFICATIONS CURRICULUM SUPPORT
Physics
Researching Physics:
Planning an Investigation
Teacher’s Notes
[HIGHER]
The Scottish Qualifications Authority regularly
reviews the arrangements for National
Qualifications. Users of all NQ support materials,
whether published by Learning and Teaching
Scotland or others, are reminded that it is their
responsibility to check that the support materials
correspond to the requirements of the current
arrangements.
Acknowledgement
Learning and Teaching Scotland gratefully acknowledges this contribution to the
National Qualifications support programme for Physics.
© Learning and Teaching Scotland 2011
This resource may be reproduced in whole or in part for educational purposes by
educational establishments in Scotland provided that no profit accrues at any stage.
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Contents
Introduction
Variables
Hypotheses
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Lesson ideas: Variables
Introduction: What is meant by variables?
Suggested activity: Identifying variables (short introduction)
Suggested activity: Indentifying different types of variables in an
investigation
Alternative suggestion: Inclusion of the above in other
practical work
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Lesson ideas: Hypotheses
Suggested activity: Developing a hypothesis
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TEACHER’S NOTES
Introduction
Variables
Whatever the constraints on teaching time, it is important that some lessons
give students a degree of autonomy in practical investigations and allow them
sufficient time to try different approaches. As well as motivating learning,
open-ended practical investigations help them to appreciate the nature of
scientific enquiry. Practical investigations can be a stimulating and
interesting part of students’ science education and while it is beneficial i f
they enjoy what they are doing it is more important that they learn through
their experiences.
Experimental work should never make students feel as if they are just
carrying out a detailed set of instructions to find out something that they
already know.
The management of open-ended practical investigations can present
challenges for the teacher. Students may have had different experiences of
carrying out investigations, having come to Higher Physics by a variety of
different routes. Different students in the same class may be carrying out
different activities, perhaps as pairs or in small groups, and be at different
stages within their investigations. A clear framework is needed to ensure that
all students continue to work successfully and at a good pa ce throughout the
allocated time. That is why it is essential that investigations are well planned,
and that students have sufficient background knowledge and are fully aware
of what is expected of them as well as knowing what they should have
achieved by the end of the investigation.
Having undertaken some web-based research, students need to revise or
perhaps learn some of the vocabulary and concepts that they should have at
their fingertips when planning an investigation by developing and testing a
hypothesis.
The first part of the work will concentrate on making sure that the students
have a clear understanding of variables and the types of variable which
feature in their investigation – the independent variable, the dependent
variable and one or more controlled variables. At Higher it is useful that
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TEACHER’S NOTES
students understand not only the concept of these variables, but also the
vocabulary.
In the design of experiments, an independent variable’s values are controlled
or selected by the experimenter to determine its relationship to an observed
phenomenon, which is the dependent variable. In such a n experiment, an
attempt is made to find evidence that the values of the independent variable
determine the values of the dependent variable. The independent variable can
be changed as required, and it is not necessary to explain these changes, they
are simply made by the investigator. The dependent variable, on the other
hand, usually cannot be directly controlled and occurs as a direct
consequence of varying the independent variable. One of the biggest
challenges many people have to deal with when looking at an independent
variable is the fact that all variables depend on something. While that may be
true, there is an easy way to determine what this variable is. Simply ask the
question: What do I need to change in order to influence, or try to influence,
the other thing? The thing that needs changed is the independent variable.
Controlled variables are also important to identify in investigations. They are
the variables that are kept constant to prevent their influence on the effect of
the independent variable on the dependent variable. Every experiment has a
controlled variable, and it is necessary to not change it, or the results of the
experiment won’t be valid.
In summary
Independent variables answer the question ‘What do I change?’
Dependent variables answer the question ‘What do I observe?’
Controlled variables answer the question ‘What do I keep the same?’
In addition to this it is useful to do some graph work to show which axis
should be use for which variable. SQA marking stipulate s this.
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TEACHER’S NOTES
Hypotheses
At this stage it is often useful to bring in the concept of the hypothesis. Often
the introduction of the hypothesis will clarify the labels on the different types
of variables when a student is having conceptual difficulties with the terms
used. So why is a hypothesis needed? A good hypothesis will help the student
to focus the investigation. It will keep them from ‘getting too involved in
details’. As they progress through the investigation they might notice that
more and more information comes out. The hypothesis will ensure that the
investigation stays on course.
A hypothesis is a tentative statement that proposes a possible explanation of
what is happening in the investigation. A useful hypothesis is a testable
statement, which usually includes a prediction. The student then goes on to
test the prediction by altering one variable in a controlled manner and
observing how it affects one other variable , with all the rest of the variables
being kept constant. Sometimes a hypothesis is described a s an
‘if...then...statement’ but that is not really enough. In scientific research it is
important that the hypothesis is reasonably formal such that a condition is
described and then a conclusion is postulated, eg ‘If skin cancer is related to
ultraviolet light, then people with a high exposure to ultraviolet light will
have a higher incidence of skin cancer’ could be classed as a good
hypothesis. A common problem is that students write a simple statement that
is a cause and effect relationship that makes a prediction, eg ‘If I eat
chocolate, then I will get pimples.’ They have to be reminded that what
makes a hypothetical statement is the idea that two things might be, but not
necessarily are, related. In other words the fail to state a proposed
relationship before making the prediction. Literally speaking, cause and
effect statements are often based on unstated assumptions. In models for
scientific research, minimising assumptions first and then stating your
hypothesis is how variables are controlled. A lo t of difficulties in writing
hypotheses can be traced back to the simple lack of writing skill but students
need to learn how to write in all subjects. Hypothesis writing is just one more
contribution to overall literacy across the curriculum.
It is unlikely that all students will reach this high level of success, so it will
be necessary to make some judgements while assessing the work to decide
whether or not a student has undertaken this aspect of the work to a
reasonable standard, while ensuring that t he more able students have a good
grasp of what would be ideal.
Students need to be reminded frequently that a hypothesis is still valid even
when results are the opposite of what is predicted because it will still shed
light on the true nature of the relationship being tested. This lowers the risks
of being wrong. For example, ‘If the period of a pendulum is related to its
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length, then the longer the pendulum the shorter the period.’ Actually the
results show just the opposite is true.
Hypotheses that predict unrelated variables are also useful. For example, ‘If
the period of a pendulum is related to its mass, then increasing the mass will
increase the period. ’As it turns out, the mass has no effect at all, as the
student will discover while testing this hypothesis. This is particularly
important as students often make the assumption that since they are testing or
investigating this, there must be a relationship and so massage the results
accordingly.
While it is important that this aspect of the cour se be looked at seriously, it is
also important that there is not too much time spent here. It could be useful,
but not necessary, if examples based on the investigations that the teacher is
expecting the student to undertake were incorporated into these i ntroductory
lessons. By the end of these lessons it would also be useful if the students
have identified the dependent and independent variables that will feature in
their own investigation as well as how the independent variable will be
altered, how measurements will be taken and how the controlled variables
will be kept constant. When the students fully understand what they are
investigating and how they are doing this a hypothesis can be made before the
practical work is undertaken.
Finally
These strategies could help to make open-ended investigations successful:
 Make clear at the start the minimum data set or equivalent required for all
groups (eg ‘Three variables need to be investigated, with at least five sets
of repeated results for each one’). Al so, make clear what written work
needs to be produced.
 At the outset of a practical session, get each student (or student group) to
agree a target with the teacher (eg ‘In this lesson we will collect at least 10
sets of results for mass against accelerat ion’). This could be done in
advance of the session.
 Organise lessons so that there are allocated times for planning, practical
work and writing up. Ideally, there should be at least one practical session
after an initial writing-up session, so that students have an opportunity to
repeat and check results, or to refine their method. This will help to
encourage students to improve their results.
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TEACHER’S NOTES
Lesson ideas: Variables
Introduction: What is meant by variables?
The purpose of the introduction is to ensure that the students have a clear
idea of what is meant by variables and are able to differentiate variables from
non-variables. This may necessitate some adaptation of their previous
assumptions and some maturity of thought. It is particularly important that
students are aware that some variables, which have perhaps been referred to
as being constant, are actually variables, which have a constant value within
the boundaries of how the students have used them. Examples of this could be
room temperature or g – the acceleration due to gravity. The second
important issue is that students are able to decide which variables are relevant
in any investigation that they are undertaking and which variables, although
present, do not affect the investigation in any w ay; so are not relevant. An
example of this is measuring speeds of an object travelling horizontally,
which is not affected by the value of g.
Suggested activity: Identifying variables (short introduction)
Resources
Sets of laminated cards with either a variable or a constant on each.
Learning intention
Students will understand what is meant by a variable and be able to
differentiate it from a constant.
The teacher can revise the idea of variables. Students should arrange these
into two groups. This could be done individually, in twos or in groups,
perhaps students working alone then sharing their findings with one another
or in a group would work well but would need more resources. Ultimately,
consensus should be reached on all the cards. Students will not have met
many constants yet but should have met enough to make this a valid exercise
and perhaps it might lead to further discussion.
This activity can also be done using the interactive white board if there is one
available.
Students may be aware of the following constants:
 speed of light in a vacuum
 electronic charge
 mass of an alpha particle
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



mass of a proton
mass of neutron
Planck’s constant
Avogadro’s number.
Note: A much-simplified version of this lesson would be to identify variables ,
but care needs to be taken that students are aware that not everything that has
a value is a variable.
Physical constants can be found at:
http://physics.nist.gov/cuu/Constants/index.html
Suggested activity: Identifying different types of variables in
an investigation
Resources
Set of laminated cards with a variable on each – optional.
Set of laminated cards with investigation suggestions. These investigations
will not be carried out.
(An interactive white board is a possible option .)
Learning intentions
Students will be able to identify all the variables that have relevance in any
investigation. Students will understand the terms independent variable,
dependent variable and controlled variable, and will be able to identify each
of these in any investigation.
By careful questioning, the teacher will ascertain that the students understand
the terms independent variable and dependent variable, and that there are
always a few other variables in an investigation, which need to be kept
constant. The teacher will also ascertain that the students can suggest ways of
controlling those variables, which need to be controlled. If the teacher feels
that it is required, students can work in pairs or in groups to discuss or clarify
these ideas. If students are struggling with these concepts teachers may
choose to work through one investigation idea with the students.
Students are given investigation cards (or the information will be put on the
whiteboard). These can be standard investigations from any level or previous
course work, eg how does the speed of a trolley at the bottom of a slope
depend on the angle of the slope? Students could work singly, in pairs or in
groups to find all the variables involved in the investigation, using the
laminated cards with the variables or simply writing them down in their
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TEACHER’S NOTES
lab book, and identify each different type of variable. It is useful for students
to be given the opportunity to collaborate in some way to reinfo rce their
learning.
Several investigations could be analysed but it is more important to spend a
bit more time analysing one or two investigations thoroughly than to skim
over the surface of many investigations.
Additional work could be undertaken at thi s stage to plan how these variables
could be measured and how the controlled variables could be kept constant,
which controlled variables are not easily controlled and what should be done
in that case.
As a final part of this work, the teacher may choose to introduce an actual
investigation that the students will undertake, although this may be left until
all the preparatory work is done.
Alternative suggestion: Inclusion of the above in other
practical work
Suggested activity: Identifying different types of variables in an
investigation
Resources
Any investigation or piece of practical work being undertaken by the student.
Learning intention:
Students will be able to identify all the variables that have relevance in any
practical work they undertake. Students will understand the terms
independent variable, dependent variable and controlled variable , and will be
able to identify each of these in all their practical tasks.
Instead of producing materials to concentrate solely on identifying variables,
this can be done as an ongoing part of all the practical work that the students
undertake. However, time should be set aside to ensure that the students have
a full and clear understanding, and an ability to use all of the terms
mentioned above.
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Lesson ideas: Hypotheses
Suggested activity: Developing a hypothesis
Resources
Set of laminated cards with investigation suggestions. These investigations
will not usually be carried out.
(An interactive white board is a possible option .)
Learning intentions
Students will be able to plan an investigation, identifying the independent and
dependent variable, and suggest a possible relationship between them using
an if...then...statement.
Perhaps starting with a very simple, whole -class activity, eg the pendulum, a
list of variables is identified. This could be done in many ways, eg think,
pair, share.
Think, pair, share
Part 1
Each student identifies as many variables as possible and then shares their
idea with a partner. After this a definitive is arrived at by any suitable
method. From that decisions are made on which variables could be varied
practically in the laboratory with the available equipment.
The next step is to create the ‘if’ statement . For this example a statement
would be ‘If the period of the pendulum depends on...’:
 the mass of the bob
 the length of the string
 the angle at which the swing starts.
The ‘then’ statement follows: ‘As the mass increases, then the period will
increase.’
At this point it is important that the full statement is sta ted. That the
hypothesis is incorrect is not at all important.
Part 2
Students could then do another one or more of these experiments in groups or
later in pairs or individually, finally ending with their own investigation.
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