Limitation Of Physical Measurements Flashcards
what do random errors effect
they affect precision
what does it mean when it says it affects precisions
they cause differences in measurements which causes a spread about the mean
can you get rid of random errors
no
what is an example of random error
is electronic noise in the circuit of an electrical instrument
how do you reduce random errors
- take at least 3 repeats and calculate a mean, this method also allows anomalies to be identified
- use computers/data loggers/cameras to reduce human error and enable smaller intervals
- use appropriate equipment (something with a higher resolution)
what does systematic error affect
they affect accuracy
how does systematic error occur
occur due to the apparatus or faults in the experimental method
what does systematic error do to the results
it causes all results to be too high or too low by the same amount
what is an example of systematic error
is a balance that isnt zeroed (zero error) correctly or reading a scale at a different angle (parallax error)
how do you reduce systematic error
- calibrate apparatus by measuring a known value, if the reading is inaccurate then the systematic error is easily identified
- in radiation experiments correct for background radiation by measuring it beforehand and excluding it from the final results
- read the meniscus ( the central curve on the surface of a liquid) at eye level (to reduce parallax error) and use controls in experiments
what is the definition of precision
precise measurements are consistent, they fluctuate slightly about the mean value - this doesn’t indicate the value is accurate
what is the definition of repeatability
if the original experimenter can redo the experiment with the same equipment and method then get the same results it is repeatable
what is the definition of reproducibility
if the experiment is redone by a different person or with different techniques and equipment and the same results are found it is reproducible
what is the definition of resolution
the smallest change in the quantity being measured that gives a recognizable change in reading
what is the definition of accuracy
a measurement close to the true value is accurate
what is the uncertainty of a measurement
is the bounds in which the accurate value can be expected to lie
what is the absolute uncertainty
uncertainty given as a fixed quantity
what is fractional uncertainty
uncertainty as a fraction of the measurement
what is percentage uncertainty
uncertainty as a percentage of the measurement
how do you reduce percentage and fractional uncertainty
you can measure larger quantities
what is a readings
is when one value is found
what is a measurement
when the difference between two readings is found
what is the uncertainty in a reading
+/- half the smallest division
what is the uncertainty in a measurement
at least +/-1 smallest division
what is the uncertainty of digital readings and given values
have it quoted or assumed to be +/- the last significant digit
what affects the uncertainty of the instrument
its resolution
what is the uncertainty for repeated data
is half the range (mean +/- range/2)
how can you reduce uncertainties
- by fixing one end as only the uncertainty in one reading is included
- or by measuring multiple instances
should the uncertainties be given in the same number of sig figs as the data
yes
when combining uncertainties if you add/subtract data what do you do with the uncertainties
you add the ABSOLUTE uncertainties
when combining uncertainties if you multiply/divide data what do you do with the uncertainties
you add the PERCENTAGE uncertainties
when combining uncertainties if your raising to a power what do you do with the uncertainties
you multiply percentage uncertainty by power
how are uncertainties shown on graphs
as error bars
what should the line of best fit go through
all error bars
how can you find the uncertainty in a gradient
can be found by lines of best and worst fit
- draw the steepest and shallowest line of worst fit it must go through all the error bars
- calculate the gradient of the line of best fit and worst fit the uncertainty is the difference between the best and worst gradients
what is the equation for percentage uncertainty in a gradient on a graph
= ((best gradient - worst gradient)/ best gradient) x 100
if the best and worst lines have y intercepts what can you find from that
the (percentage) uncertainty of the y intercept using the same equation as the gradient
what can be used on a graph to calculate the percentage uncertainty
the average of the two max and min lines max gradient-min gradient/2 x 100
