P3 - Practical skills Flashcards
What are the two types of error?
Random error
Systematic error
What is random error? e.g?
Random errors cause the results to spread about the true value due to the results varying in an unpredictable way, measuring something 20 times your head is in slightly different position each time so your creating random error
what is systematic error? e.g?
systematic errors usually cause each reading to be different to the true value by the same amount - ie they shift all your measurements. e.g using an inaccurate clock
How can you reduce uncertainty?
Repeat the experiment several more times, more repeats means more precise data. Also this allows to check for any anomalies in the results
Take averages because the more measurements you average over the less random error you are likely to have
Using best equipment. The higher the resolution the more accurate the result
What should you split uncertainties into?
what’s the difference?
readings are taken from 1 measurement as 0 is assumed to have no uncertainty. e,g thermometer
measurements are taken from 2 things so there are two uncertainties, e.g ruler
what are the uncertainties value in a reading?
The uncertainty of a reading (one judgement) is at least ±0.5 of the smallest scale reading.
what is the uncertainties value in a measurement?
The uncertainty of a measurement (two judgements) is at least ±1 of the smallest scale reading.
What is the uncertainty in given data on data sheet?
In all such cases assume the uncertainty to be +-1 in the last significant digit.
what is the uncertainty when there are repeats?
If measurements are repeated, the uncertainty can be calculated by finding half the range of the
measured values.
how do you draw error bars?
plot the data point at the mean value
calculate the range of the data, ignoring any anomalies
add error bars with lengths equal to half the range on either side of the data point.
how do you find percentage uncertainty in a graph of error bars?
percentage uncertainty = |best gradient−worst gradient| over best gradient x 100
what is absolute uncertainty?
the uncertainty of a measurement given
How do you find percentage uncertainty?
absolute uncertainty/ measurement x 100
What is zero error?
error involving not taking 0 as the correct measurement
what is parallax error?
error by not being in eye level with the object
