Planning an experiment

Know the difference between ‘precise’ (fineness of scale devisions) and ‘accurate’ (closeness to true value).

Explain the advantages of dataloggers. When timing oscillations measure at least 20 twenty in total (e.g. a

minimum of 2 sets of 10 oscillations). Rather than single results take a range to plot a graph, best fit a curve

and take a gradient that is less sensitive to random error.

Taking results

Place a ficidual mark to aid the timing of a pendulum (this must go under the pendulum at the equilibrium position for minimum transition time).

Place a ficidual mark to improve accuracy when measuring the extension of a material.

Use a mirror to eliminate parallax error. Be able to draw a sketch of the above three techniques. Use a set square to ensure an object (e.g. metre rule) is vertical. This

needs to be placed at two perpendicular surfaces to ensure the object is vertical in both planes.

Units that are name after people must start with a capital letter e.g. ‘Volt’.

Ensure the independent variable is given at the precision used e.g. 5.0cm not 5cm if measuring with a ruler – because you are controlling it doesn’t mean it should be truncated.

Measure the diameter of cylindrical objects (e.g. wire) by using the instrument at three different angles in three different positions (at least – take more readings if there is a lot of variation).

Record results to the max number of sig fig available. Record zero as ‘0.00’ if you are measuring to 2 dp (marks are removed if you do not do this.)

Plotting graphs

If a variable is defined in a question (e.g. x = deflection of metre rule) then use it on the axes label.

A best fit curve or line must not be drawn with thick pen, it must not be sketchy or feint. It must have an even number of data points on either side.

Ensure numbers are put on scale at least every 5cm. The examiners penalise marks for points marked as ‘blobs or dots’. They

require that points are marked with ‘+’ (and not ‘x’)

Analysing data

Use a mirror to draw a normal to a best fit curve. Use a protractor to place a tangent perpendicular to the normal. Draw a large triangle extending from a tangent in order to calculate

gradient or inverse gradient. Draw construction lines and label with values to show how you took the

gradient – ‘unless clear evidence of working is show full credit cannot be given’.

Understand that in the context of practical papers ‘Evaluate’ can mean work out e.g. ‘Evaluate the force if the mass = 3kg and the acceleration =10ms-2 ’.

Express answers to the minimum number of sig fig given in the question. Don’t truncate the significant figures during working. Don’t give the final answer to more than 4 sig. fig. Don’t truncate valid data e.g. 638mm 64cm. When multiplying and dividing add %error. When adding and subtracting add uncertainties.

Describing experiment

Where a lot of marks are given use bullet points to ensure all are achieved.

Include instruments used, measurements to be made, graphs to be plotted, results processing required.

Be specific (pedantically so) e.g. when asked how to check that a ruler was horizontal students answered that ‘they measured the height from

the floor at both ends’. They were not awarded a mark as they omitted to say that they ‘check that both heights were the same’.