2 Limitation of physical measurement Flashcards
give three ways to 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, e.g a micrometer has higher resolution (0.1 mm) than a ruler
(1 mm).
what do random errors affect
Random errors affect precision, meaning they cause differences in measurements which causes
a spread about the mean. You cannot get rid of all random errors.
what do systematic errors affect
Systematic errors affect accuracy and occur due to the apparatus or faults in the experimental
method. Systematic errors cause all results to be too high or too low by the same amount each
time.
give three ways to reduce systematic errors
● Calibrate apparatus by measuring a known value (e.g. weigh 1 kg on a mass balance), 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 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 absolute uncertainty determined by
absolute uncertainty is determined by the resolution if the scale n the measuring instrument
how would you work out absolute uncertainty (A.U.)
A.U. = 1/2 the smallest division
how would you work out the fractional uncertainty (F.U.)
F.U. = A.U. / measurement
how would you work out percentage uncertainty (P.U.)
P.U. = F.U. x 100
how would you work out absolute uncertainty (A.U.) for repeated measurments
A.U. = 1/2 the range
how would you work out the fractional uncertainty (F.U.) for repeated measurements
F.U. = A.U. / mean
how would you work out percentage uncertainty (P.U.) for repeated measurements
P.U. = F.U. x 100
what does the measurement need to be ≤ to be within the bands of accepted experimental uncertainty for P.U.
10%
