3.1 Measurements and their Errors Flashcards
(25 cards)
What are the 6 SI units? What are they for?
Metre (length), second (time), kilogram (mass), ampere (electric current), kelvin (temperature), mole (substance amount)
Conversion from eV to J
x 1.6 x10^-19
Value of all the (big) prefixes
T x10^12
G x10^9
M x10^6
k x10^3
Value of all the (small) prefixes
c x10^-2
m x10^-3
micro x10^-6
n x10^-9
px10^-12
f x10^-15
Conversion from kWh to J
x3.6x10^6
How to reduce random errors?
By repeating steps and creating a mean (ignoring anomalies)
What is a systematic error?
Difference from true value but by the same amount each time
How to reduce systematic error?
Change method/ person doing experiment, use better instruments, be more careful in general
What is the difference between readings and measuremnts?
Readings have only one judgement, whereas measurements have two.
How do you find out the absolute uncertainty of something?
Look at the upper and lower limits of the mean value.
Half of the measuring instrument’s smallest scale division.
How do you find the percentage uncertainty of something?
(absolute uncert./measured value) x100
How do you find the fractional uncertainty of something?
absolute uncert./measured value
How do you combine uncertainties when multiplying quantities?
add them together
How do you set an object vertically?
Use a set square perpendicular to the object (and bench)
How do you set an object horizontally?
Use a set square to align the object perpendicular to a vertical ruler
What are the two scales of a micrometer and where are they?
main scale - on the sleeve/ barrel
thimble scale - rotating scale on the thimble
What is each division equal to on the main scale of a micrometer?
0.5mm
What is each division equal to on the thimble scale of a micrometer?
0.01mm
What is the purpose of the rachet on the end of a micrometer?
prevents the user from tightening the object too hard and damaging the micrometer/ the object.
How do you eliminate a zero error reading?
add/ subtract the error to each reading taken with that instrument
How do callipers measure the internal diameter of an object (e.g. a tube)?
P lace the two prongs inside the tube. Adjust the moving part of the callipers until the prongs just grip the inside of the tube
Would micrometer of calliper be better for taking many measurements and why?
calliper; it may have less accuracy but it is quicker to use
What is the difference between readings and measurements?
readings come from single judgements from a piece of equipment, whereas measurements come from the difference between two judgements
How to figure out uncertainty from a stated value given e.g. 1.60x10^-19
± 1 of the last significant digit (e.g. ±0.01x10^-19)
