Measurements and their errors Flashcards
What are SI units?
fundamental (base) units of physical quantites
What is the SI unit of mass?
kg (kilogram)
What is the SI unit for an amount of a substance? (mole)
mol
What is the SI unit for current?
A (amperes)
What is the SI unit for temperature?
K (kelvin)
What is the SI unit for length?
m (metres)
What is the SI unit for time?
s (seconds)
What is the standard form for T, Tera?
10^12
What is the standard form for G, Giga?
10^9
What is the standard form for M, Mega?
10^6
What is the standard form for k, kilo?
10^3
What is the standard form for c, centi?
10^-2
What is the standard form for m, milli?
10^-3
What is the standard form for µ, micro?
10^-6
What is the standard form for n, nano?
10^-9
What is the standard form for p, pico?
10^-12
What is the standard form for f, femto?
10^-15
Express 60T ohms in standard form
6 x 10^13
T= tera, 10^12
Write 0.000003m with a suitable prefix
3µm
What is the actual value of 8M ohms?
8,000,000 ohms or 8 x 10^6 ohms
What is something to remember about s.f.?
-the answers should be given with the same number of s.f. as the value with the least amount of s.f. used in the calculation
-in tables, all data needs to have the same s.f.
What do we mean by accuracy?
how close a measurement is to the accepted (true) value
What do we mean by precision?
how close measurements are to each other and the mean
What is a random error?
these are errors in measurements which are unpredictable
How can we reduce random errors? (3)
-repeat readings and find a mean
-use best-fit graph lines
-use computers/data loggers/cameras to reduce human errors e.g. reaction times
What is a systematic error?
-errors which occur due to the apparatus or faults in the experimental method
-these cause all results to be too high or too low by the same amount each time
How can we reduce systematic errors? (3)
-calibrate equipment
-use graph gradients to calculate values
-read measurements at eye level
What is a zero error and how can we fix this?
-equipment that isn’t zeroed correctly
- take away starting reading from total when an object is measured
What is a parallax error and how can we fix this?
-reading a scale at a different angle which can make the measurement seem off
-read the measurement at eye level
What do we mean when an experiment is repeatable?
when the experiment is repeated with same method and equipment and achieves the same result
What do we mean when an experiment is reproducible?
when the experiment is repeated using different equipment or method but still achieves the same result
What is resolution?
the smallest increment on an apparatus
What is uncertainty?
the bounds in which the accurate value can be expected to
lie
How can we find the absolute uncertainty from a single judgment?
half the resolution
How can we find the absolute uncertainty from two judgements?
2 x half the resolution
How can we find the absolute uncertainty from repeat readings?
1/2 x range
How can we find the absolute uncertainty from combined readings?
divide absolute uncertainty by no. of objects
What s.f should the uncertainties be?
same as the data used
How can we find fractional uncertanties?
absolute uncertainty of value/ value
How can we find percentage uncertainties?
(absolute uncertainty of value/ value) x 100
What do we do with the uncertainties when adding/subtracting data?
add absolute uncertanties
What do we do with the uncertainties when multiplying/dividing data?
add percentage uncertanties
What do we do with the uncertainties when we raise the data to a power
multiply percentage uncertainty by the power
How can we show uncertainties on a graph?
use error bars
How can we calculate the gradient percentage uncertainty from a graph?
-draw a steepest and shallowest line of worst fit, it must go through all the error bars.
-draw a ‘best’ line of best-fit which passes all the points close as possible
percentage uncertainty= (best gradient - worst gradient/ best gradient) x 100
How can we calculate the y-intercept percentage uncertainty from a graph?
-draw a steepest and shallowest line of worst fit, it must go through all the error bars.
-draw a ‘best’ like of best-fit which passes all the points close as possible
percentage uncertainty= (best y-intercept - y-intercept/ best y-intercept) x 100
