Measurements and their errors

Question 1

absolute uncertainty

Answer 1

uncertainty given as a fixed quantity

Question 2

combing uncertainties: multiplying/dividing data

Answer 2

ADD PERCENTAGE uncertainties

Question 3

combing uncertainties: adding/subtracting data

Answer 3

ADD ABSOLUTE uncertainties

Question 4

combing uncertainties: raising to a power

Answer 4

MULTIPLY PERCENTAGE uncertainty by the power

Question 5

define precision

Answer 5

Precise measurements are consistent, they fluctuate slightly about a mean value - this doesn’t indicate the value is accurate

Question 6

define accuracy

Answer 6

A measurement close to the true value is accurate

Question 7

define repeatability

Answer 7

If the original experimenter can redo the experiment with the same equipment and method then get the same results it is repeatable

Question 8

define reproducability

Answer 8

If the experiment is redone by a different person or with different techniques and equipment and the same results are found, it is reproducible

Question 9

define resolution

Answer 9

The smallest change in the quantity being measured that gives a recognisable change in reading

Question 10

Fento

Answer 10

10^-15

Question 11

fractional uncertainty

Answer 11

uncertainty as a fraction of the measurement

Question 12

Giga

Answer 12

10^9

Question 13

how are uncertainties shown on a graph

Answer 13

error bars

e.g. if uncertainty is 5mm, then 5 squares of error bars on either side of the point

line of best fit should go thru all error bars

Question 14

how can SI units of quantities be derived

Answer 14

using their equations

e.g. F = ma ———–> kgms-2 which is N

Question 15

how many sig figs to give uncertainty to

Answer 15

same number of sig figs as the data

Question 16

how to find uncertainty in y intercepts

Answer 16

best y-intercept - worst y-intercept (using libnes of best and worst fit)

Question 17

how to find uncertainty of a gradient

Answer 17

by lines of worst and best fit

draw steepest and shallowest lines of best fit - both must go through ALL error bars

the uncertainty is the difference between gradients

Question 18

how to reduce random errors

Answer 18

take at least 3 repeats and calculate a mean - allows you to identify anomalies

use computers/data loggers to reduce human error

use appropriate equipment e.g. higher resolution

Question 19

how to reduce systematic error

Answer 19

calibrate apparatus by measuring a known value - can identify innacuraccies

if radiation experiement - correct for background radiation

read at eye level to reduce parallax error

use controls in experiments

Question 20

how to reduce uncertainty

Answer 20

reduce no. readings in a measurement e.g. fixing one end of a ruler

measuring multiple instances, e.g. taking 10 and dividing by 10 to find 1 (uncertainty is also divided by 10)

Question 21

mega

Answer 21

M 10^6

Question 22

micro

Answer 22

mu 10^-6

Question 23

Nano

Answer 23

n 10^-9

Question 24

percentage uncertainty

Answer 24

uncertainty as a percentage of the measurement

Question 25

Pico

Answer 25

p 10^-12

Question 26

Tera

Answer 26

T 10^12

Question 27

uncertainty

Answer 27

0.5 * range

% uncertainty = uncertainty / mean * 100

if all data is the same the uncertainty is the resolution

Question 28

uncertainty for digital readings

Answer 28

+ or - the last significant digit

Question 29

what are systematic errors

Answer 29

cause all results to be too high/low by the same maount each time e.g. zero error or parallax error

usually occur due to apparatus or faults in method

Question 30

what are the SI units

Answer 30

fundamental units:
Mass (m): kg (kilograms)
Length (I): m (metres)
Time (t): s (seconds)
Amount of substance (n): mol (moles)
Temperature (t): K (kelvin)
Electric current (I): A (amperes)

Question 31

what do random errors effect

Answer 31

precision - cause difference in measurements which cause a spread about the mean

Question 32

what do systematic errors effect

Answer 32

accuracy

Question 33

what is uncertainty

Answer 33

bounds in which the accurate value can be expected to lie