Uncertainties

Question 1

define accuracy

• how do you improve this

Answer 1

how close the values are to the true value

• reduce systematic errors

Question 2

define precision

• how do you improve precision

Answer 2

measurements are close together in their value

• reduce random errors

Question 3

define resolution

Answer 3

smallest non 0 value the device can read

(smallest detectable change)

Question 4

define repeatable

Answer 4

an experiment that can be done again, the same way and get the same results

Question 5

define reproducible

Answer 5

the experiment can be done by a diff person/diff method and get the same end results

Question 6

what is a true value

Answer 6

the value obtained from an ideal experiment

Question 7

define error

Answer 7

the difference between the measured value and the true value

Question 8

define uncertainty

Answer 8

quantification of doubt about the measured results/instruments precision

Question 9

how do you calculate the overall % uncertainty

(3)

Answer 9

1) uncertainty of measurements given either by the precision of the instrument OR half the range, whichever is larger
2) %U = (U / mean of result) x100
3) always add the uncertainties no matter the equation

(unless there is a power of the value, then; %U x power)

Question 10

How do you plot uncertaintys of values on a graph

Answer 10

add an error bar (highest and lowest value recored)

Question 11

how do you calc uncertainty from graphs

Answer 11

the difference between the line of best ft going through the mean values and most different gradient

(worst gradient is drawn from either the l_ine of best fit through the highest / lowest points of the error bars_)

Question 12

what is it key to know about your results relative to the units given

Answer 12

results are always quoted to the lowest possible amount of sig.figs given by the value with the loses sig.figs. ,

Question 13

What are random errors

Answer 13

• repeating measurement gives you various results, spreading them from the true values
• unpredictable / uncontrollable

Question 14

what are systematic errors

Answer 14

where the same influence affects all readings of the measurements, each differing by the same amount

• brought up by the system

Question 15

what are the usual precision of instruments

• what is it for stop watches

Answer 15

+- 0.1

+-0.3 (human reaction time to press button)

Question 16

How do you reduce systematic errors

(2)

Answer 16

• removing/knowing zero errors, use calibers to ensure device reads 0 when it should
• reduce human errors by using computers / data loggers

Question 17

How do you reduce random errors

(5)

Answer 17

• do repeats to get you a better average
• ignore anomalous results
• use more precise instruments/high revolution
• be eye level; ith scales, reduces parallax error
• having a smaller range per result

Question 18

define reliable

Answer 18

constant value obtained each time with the measurement repeated

Question 19

defne valid

Answer 19

the measurements taken are appropriate and required for the data

Question 20

define linearity

Answer 20

this is a design feature of instruments

• reading is directly proportional to the vait=rable that a=causes the reading to change (parallax error, not eye level)