unit 5 practical Flashcards
independent variable definition
the variable for which the values are selected by the investigator
dependent variable definition
the variable for which the values change when the independent variable is changed
controlled variable definition
a variable which may affect the outcome of the investigation and therefore should be kept constant
range definition
the maximum and minimum values of the independent or dependent variables. this shouldnt be too big or too small
valid conclusion definition
a conclusion supported by valid data, obtained from an appropriate experimental design and based on sound reasoning
validity of experimental design definition
- suitability of investigative procedure to answer the question being asked.
- strategies to ensure validity include fair test and controls that aim to isolate the effect of the independent variable on the dependent variable
resolution definition
this is the smallest change in the quantity being measured by a measuring instrument that can be observed
- e.g +/- 1mm on a 1m ruler
anomaly definition
value in a set of results which is judged not to be part of the inherent variation
true value definition
this is the value that would be obtained in an ideal measurement
uncertainty definition
the interval within which the true value can be expected to lie
e.g the temperature is 20°C +/- °C
measurement error definition
the difference between a measured value and the true value
systematic error definition
- these cause readings to differ from the true value by a consistent amount each time a measurement is made
- systematic errors can include the influence of the environment, the methods of observation or the instruments used
- the effect of systematic errors cannot be reduced by increasing repeats
random error definition
- these occur due to results varying in an unpredictable way from one measurement to the next
- the effect of random errors can be reduced by taking more measurements and calculating a mean
accuracy definition
a measurement result is considered accurate if it is judged to be close to the true value
precision definition
- this shows the closeness of agreement between measured values
- it gives no indication of how close results are to the true value
repeatability definition
the precision obtained when repeat readings are obtained by a single learner/group
repeatable definition
- a measurement is repeatable, if repetition by a single learner/group using same method and equipment, obtains the same or similar results
reproducability definition
the precision obtained when repeat readings are obtained by a different learner/group
reproducible definition
- a measurement is reproducible if repetition by different learners/groups obtains the same or similar results
- this could include using different equipment/methods
- this is a harder test of the quality of data
hazard definition
- a chemical or piece of apparatus that could cause harm
- it is expected that in risk assessments the nature of the hazard is also specified
risk definition
an action involving a hazard that might result in danger
control measures definition
something that can be done to reduce or prevent a risk while allowing you to carry out the experiment
what are the 3 types of specified practical work in the spec?
- investigative work
- microscopy
- dissection
in an experimental design, you should be able to:
- identify the independent variable - the factor that tests/changes
- identify the dependent variable - the factor that you are measuring
- identify the controlled variables - the factors that you need to keep constant
- use the correct units for all your variables
- identify a suitable range for your independent variable, this would normally be at least five values
- explain why repeat readings would be needed - a mean is more reliable than an individual reading and it will help identify anomalous results
- design a suitable control experiment
- assess the main risks of your experiment