Practical Skills

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Drawing Graphs

When drawing graphs you must ensure that you follow these guidelines

• Graphs must be an appropriate size, filling most of the space available
• Scales should use appropriate, even spacings
• Axes should be labelled correctly (i.e. Mean time taken/secs)
• Lines of best fit should not go beyond the points
• A single line of best fit should be drawn with a pencil - it can be curved or straight
• Points should be small crosses

Scatter graphs should be used for continuous data and bar charts should be used for discontinuous data

The independent variable should go on the x - axis (horizontal) and the dependant variable should go on the y - axis (vertical)

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Working with data

Calculating the mean

• Calculate to 2 dp (unless working with times - nearest second)
• Show working out if possible
• Double check if using calculator to avoid input errors

Calculating rates

• always n / time taken (secs)
• Be aware of whether you should use mean time taken or individual time taken
• Units should always be same as calculation (e.g. ml/sec)
• Check - as time increases for reaction rate decreases
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Reliability

Recognising reliability

• All results are very similar
• All results are grouped very closely together (small range)

A mean is more reliable when there is a small range and several repeats

Improving reliability

• More repeats
• More intermediate values
• Ignoring or retesting anomalous results
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Accuracy and precision

Using suitable measuring equipment and using the equipment correctly improves the accuracy and precision of an experiment.

To be accurate, reading must be as close to their true value as possible

To be precise, readings must be close together

Eg - if I weigh out 6.579g, and 6.580g my readings are precise, but if i had left a pen on the balance while I weighed them, they would not be accurate

Note - this often is mentioned when we look at timings as reaction times affect the precision of a stopwatch

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General tips

Follow instructions carefully - read through all the instructons, highlighting important ones.

Follow the instructions at all times - never do anything from memory

Check your results to avoid anomalous data

Read all questions carefully - word for word

Use data from tables to support and illustrate your answer, especially when describing or explaining trends

Use scientific vocabulary at all times

Double check all calculations and figures from graphs

Always use units

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