Errors & Uncertainties (CIE AS Physics)

• Measurements of quantities are made with the aim of finding the true value of that quantity
• In reality, it is impossible to obtain the true value of any quantity, there will always be a degree of uncertainty
• The uncertainty is an estimate of the difference between a measurement reading and the true value
• Random and systematic errors are two types of measurement errors which lead to uncertainty

 

Random error

• Random errors cause unpredictable fluctuations in an instrument’s readings as a result of uncontrollable factors, such as environmental conditions
• This affects the precision of the measurements taken, causing a wider spread of results about the mean value
• To reduce random error: repeat measurements several times and calculate an average from them

 

Systematic error

• Systematic errors arise from the use of faulty instruments used or from flaws in the experimental method
• This type of error is repeated every time the instrument is used or the method is followed, which affects the accuracy of all readings obtained
• To reduce systematic errors: instruments should be recalibrated or the technique being used should be corrected or adjusted

Representing precision and accuracy on a graph

 

Zero error

• This is a type of systematic error which occurs when an instrument gives a reading when the true reading is zero
• This introduces a fixed error into readings which must be accounted for when the results are recorded

• Precision of a measurement: this is how close the measured values are to each other; if a measurement is repeated several times, then they can be described as precise when the values are very similar to, or the same as, each other
• The precision of a measurement is reflected in the values recorded - measurements to a greater number of decimal places are said to be more precise than those to a whole number
• Accuracy: this is how close a measured value is to the true value; the accuracy can be increased by repeating measurements and finding a mean average

 

The difference between precise and accurate results