Measurements and their errors Flashcards
T prefix
10^12
G prefix
10^9
M prefix
10^6
k prefix
10^3
m prefix
10^-3
micro prefix
10^-6
n prefix
10^-9
p prefix
10^-12
f prefix
10^-15
SI unit for mass
kg
SI unit for length
metres
SI unit for time
seconds
SI units for temperature
kelvin
SI unit for amount of a substance
Moles
SI unit for current
Amps
Alternative unit for joules
eV and kWh
What is an eV
Electron volt - energy required to accelerate an electron from rest through a pd of 1 volt
How many joules in an eV
1.6 x 10^-19
What is a kWh
Killowatts per hour, 1000 watts in an hour
How many joules in a kWh
3.6 x 10^6
How many types of errors are there
2
Types of errors
Random, systematic
What do random errors affect
Precision
How can you reduce a random error
Repeating and finding mean, using computers, use equipment with higher resolution
What causes systematic errors
Experimenter, instruments or method
What do systematic errors affect
Accuracy
How can you reduce a systematic error
Changing method or equipment, calibrate (measure known qty’s to check equipment), read meniscus at eye level (curve of liquid), use controls, subtract background results (background radiation)
What is accuracy
How close your results are to true value
What is precision
Having similar values
What is repeatability
When the same person can get the same results each time with equipment and method
What is reproducibilty
When other people can the same results with different equipment or method
What is resolution
Scale of the instruments
Key features of a reading
Single judgement, absolute uncertainity is +/- half of smallest scale of division
Example of an instrument that gives readings
Thermometer
Key features of a measurement
Two judgements, chance for inaccuracies at either end of scale, absolute uncertainty is +/- smallest scale of division
Example of an instrument that gives measurements
Ruler, protractor
How to reduce fractional or percentage uncertainty
Measure larger quantities
Uncertainity of digital readings
Will either be told/known or can be assumed to be +/- the last significant digit - so resolution affects uncertainty
Uncertainity of a mean value
Half the range (largest - smallest value found)
Percentage uncertainty for a single reading
Abosolute uncertainity / measure value
Percentage uncertainty for a repeated reading
Half of range / mean value (range is largest-smallest value)
How to reduce uncertainty
Fix one end of ruler measuring a large space/instance and then dividing to find the required space/instance
How many significant figures to give the uncertainty to
Same as the significant figures of the data
Percentage uncertainty of gradient
|(LOBFm - WALOBFm)| / (LOBFm) *100
Percentage uncertainty of the Y-intercept
|(LOBFc - WALOBFc)| / (LOBFc) * 100
Absolute uncertainity of x when x = y + z
Absolute uncertainty of x = absolute uncertainty of y + absolute uncertainty of z
Percentage uncertainty of x when x = yz
Percentage uncertainty of x = percentage uncertainty of y + percentage uncertainty of z
Percentage uncertainty of x when x = y/z
Percentage uncertainty of x = percentage uncertainty of y + percentage uncertainty of z
Percentage uncertainty of x when x = y^a
Percentage uncertainty of x = (percentage uncertainty of y) * a
How to show uncertainties on a graph
Error bars - line of best fit must go through all
What is LOBF
Line of best fit
What is WALOBF
Worst acceptable line of best fit
How to find percentage uncertainty using max and min gradient
(max gradient - min gradient) / 2 * 100
Order of magnitude of wavelength of light
10^-7
Order of magnitude of mass of Earth
10^24
Order of magnitude of mass of sun
10^30
