measurements and errors Flashcards
what are the base SI units
Candela- cd (Luminos intensity), Metre- m (length), Kelvin- K (temperature), Mole- mol (chemical mass), Ampere- A (electrical current), kilogram- Kg (mass), Second- s (time)
What are other useful SI units
Celsius- `C (temperature), Joule- J (energy), Ohm- omega (resistance), Tesla- T (magnetic flux density), Hertz- Hz (frequency), Pascal- Pa (pressure), Newton- N (force), Coulomb- C (charge), Watt- W (power), Volt, V (P.d)
unit prefixes
Nano- nm (10^-9), Micro- um (10^-6), Milli- m (10^-3), Centi, c (10^-2), kilo- K (10^3), Mega- M (10^6), Giga- G (10^9)
what are the observed value, true value and error
observed value- the measurement you make
True value- what the measurement should be
error- uncertainty about our measurement (the difference between observed and true value)
the 2 parts of an error model
random error- follows no pattern (reduced by doing experiment multiple times)
Systematic error- follows a set pattern also known as zero error (reduced by calibration e.g weighing a known mass)
what is the precision of the measurement system
how close repeated measurements are to each other
what makes a measurement repeatable
if the same person does the same experiment with the same apparatus and gets the same results
what makes a measurement reproducible
if a different person can perform the experiment with the same apparatus and get the same result
what is the resolution of a measuring instrument
it describes its maximum precision
define uncertainty
a measure of how confident you can be in a measurement
what is the absolute uncertainty
The range of possible real values (e.g + or - 5)
what is the fractional uncertainty and percentage uncertainty
the absolute uncertainty divided by the measured value (percentage uncertainty is this as a per cent)
what is an error bar
a line on an uncertainty graph showing the range of possible values. they can be used to find the steepest and shallowest line of best fit
how can uncertainty be spotted from a graph
if the theory and the results do not match when the independent variable is zero
how do you calculate the uncertainty in a measurement on a graph
the steepest possible line of best fit has a gradient g1
the shallowest possible line of best fit has a gradient of g2.
uncertainty= (g1+g2)/2 + or - (g1-g2)/2