Variables When scientists undertakes aninvestigations they will look to find a relationship between two variables.There are different types of variables and these can be described or measured in different ways. 21 February, 2011
Types of variables• Independent variable: This is the variable that you change during the experiment. You set the value for each reading.• Dependent variable: This is the variable that is measured during the experiment in order to find out how the independent variable affect it.• Control variables: These are the variables that are kept constant during the experiment in order the make the test fair.
Example In this experiment the ability of different metals to conduct heat is investigated. The time it takes for the heat to flow through the metal and melt the wax holding the match is measured.Independent variable = type of metalDependent variable = time it takes for the match to fallControl variables = length and thickness of the metal rods.
Description of variables• Continuous variable: This type of variable can take any numerical value. We usually use line graphs with these.• Discrete variable: his type of variable has certain fixed values only – usually whole numbers.• Categoric variable: This type of variable is described by words. They have no numerical value. We usually use bar charts with these.
Examples In this experiment the ability of different metals to conduct heat is investigated. The time it takes for the heat to flow through the metal and melt the wax holding the match is measured.Type of metal = categoric variableTime it takes for the match to fall = continuous variableThere are no discrete variables in this experiment
Errors• Systematic error: this is an error in the way in which the investigation is being done – the error will always occur until the method is changed.• Random error – this is a one off error – usually due to an incorrect reading of an instrument.• Zero error – this is an error on the instrument being used – all the reading will be incorrect because the instrument is not calibrated correctly.
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