1. First of all we can read the aims from the specification:
3.3 Assessment details
This unit is assessed by means of a written examination paper. The
assessment for this unit covers planning an experiment, analysing data and
drawing conclusions. A laboratory is not required for this assessment.
Planning Students will be expected to plan an experiment that is set by
Edexcel, although they will not be expected to carry it out.
Students may be required to:
 identify the apparatus required
 discuss calibration of instruments, eg whether a meter reads zero
before measurements are made
 describe how to measure relevant variables using the most
appropriate instrument and correct measuring techniques
 identify and state how to control all other relevant variables to make
it a fair test
 discuss whether repeat readings are appropriate
 identify health and safety issues and discuss how these may be dealt
with
 discuss how the data collected will be used
 identify possible sources of uncertainty and/or systematic error and
explain how these may be reduced or eliminated
 comment on the implications of physics (eg benefits/risks) and on its
context (eg social/environmental/historical).

2. You should remember and take into account the next points:
Difference between accuracy and precision:
Accuracy is referred to how far a measurement is from the real value. Precision is
referred to the total uncertainty that a measurement has(because of the significant
figures)
Accuracy is affected by the systematic errors (uncertainties) like zero error, parallax
error, time of reaction... Accuracy can be improved by repeating measurements
and taking the main value, or trying to get a line of best fit (These both options are
considered as methods to improve accuracy). Accuracy can also be improved by
adjusting the zero error, the point of view or even by ensure a straight movement
of objects (measuring vertically ensuring with a set square), starting from rest, etc…
(You should realize the difference between methods and precautions to improve
accuracy). Of course you can improve accuracy if you use apparatus like light gates to
take time measurements (this will eliminate the human time of reaction; if you use this,
take care about naming data logger + to computer)
Precision is affected by random errors, like all those that can be due to the changes in
the conditions of measurements. Precision can be improved (but it will never be
perfect) by using instruments with better resolutions (the smallest measurement
that can be taken: calipers/micrometers for lengths if it is able, digital scales for
masses, wider measuring cylinders for volumes…) or by adjusting with a line of best
fit. Also by calculating a gradient with a longer line.
Calculations:
Don’t forget to follow the number of significant figures (s.f) while you get an average
value from a set of measurements. Also remember to express the result of a
calculation with the same number of s.f. of the measurement that has the smallest one.
Making an average value will increase accuracy but not precision, so don’t put more
s.f. Remember that if you have an uncertainty value, the this will fix directly the last s.f.
of the measurement.
When doing averages, the uncertainty must cover all the values all of the set of
measurements. The percentage difference to show whether the measurements are
consistent is calculated by:
𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑚𝑒𝑛𝑡 − 𝑟𝑒𝑎𝑙 𝑣𝑎𝑙𝑢𝑒
%𝑒𝑟𝑟𝑜𝑟 =
𝑟𝑒𝑎𝑙 𝑣𝑎𝑙𝑢𝑒
Information from graphs:
Think about the units in the two axes and hence get the units for the gradient (units in
axe “y” divided units in axe “x”), the area under the graph (units in axe “y” times units
in axe “x”), and both intercepts will have the same units of each axe.
Safety precautions:
Any logical comment can be accepted but usually they look for, avoiding burnt, kicked,
spoiled or damaged in any part of the body, specially in the face (using goggles or lab
robes are usually a good option)

3. Explaining an experiment:
Choose the correct formula you must use to achieve the experiment. Identify the
variables and the constant values. Choose the independent and the dependent
variables and try to keep constant the rest of them if it is needed. Think about the
instruments needed to measure both variables and the method to change the
independent one in order to get a line of best fit (if there is no chance to change one
of them, then you should repeat measurements to increase accuracy). Recall the
information from graphs to explain the calculations. See in “precautions to improve
accuracy” to show the best way to do it. Rearrange equations to show calculations.
Always try to look for the form: y=mx+c. Ensure that “m” and “c” are constant.
Criticizing measurements:
For a line of best fit are needed at least six measurements.
All the measurements of the same set must have the same precision.
The range of measurements for a line of best fit must be as large and steeply
proportional as possible.
Precision of the measurements must be reasonably good.
All the measurement must have units.
Doing graphs and calculating gradients and areas:
Once you have all the points written in the table transpose them to the graph trying
to get the largest graph in the sheet that is possible. Choose the line of best fit just
by using only the points you fixed (don’t use the origin unless you got it as a point).
Draw the line leaving the same number of points at each side of the line (think that
you must choose the smallest sum of distances from the points to the line).
To calculate areas, just divide always the total area in rectangles and triangles (if it
is needed you can count squares).
To calculate gradients use always the largest line you can use (even extrapolating
the straight line if you can (this is a way of improving precision)
Don’t forget to show the units of whatever you calculate.