Exam terms

Zero error

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero eg the reading on an mass balance failing to return to zero when nothing is being weighed.  A zero error may result in a systematic error. 

Validity

Suitability of the investigative procedure to answer the question being asked. For example, an investigation to find out if the rate of a chemical reaction depended upon the concentration of one of the reactants would not be a valid procedure if the temperature of the reactants was not controlled. 

Use

In the context of the exam questions this means that: your answer must be based on the information given in the question. You might also be expected to give  your own knowledge and understanding but unless the information given in the question is used no marks can be given. Make sure you consider all the …

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Uncertainty

The interval within which the true value can be expected to lie with a given level of confidence or probability. eg ‘the temperature is 20 °C ± 2 °C at a level of confidence of 95%’  The level of confidence part of this definition is just a statistical measure related to how precise (spread out) …

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