Limitation Of Physical Measurements

Question 1

what do random errors effect

Answer 1

they affect precision

Question 2

what does it mean when it says it affects precisions

Answer 2

they cause differences in measurements which causes a spread about the mean

Question 3

can you get rid of random errors

Answer 3

no

Question 4

what is an example of random error

Answer 4

is electronic noise in the circuit of an electrical instrument

Question 5

how do you reduce random errors

Answer 5

• 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)

Question 6

what does systematic error affect

Answer 6

they affect accuracy

Question 7

how does systematic error occur

Answer 7

occur due to the apparatus or faults in the experimental method

Question 8

what does systematic error do to the results

Answer 8

it causes all results to be too high or too low by the same amount

Question 9

what is an example of systematic error

Answer 9

is a balance that isnt zeroed (zero error) correctly or reading a scale at a different angle (parallax error)

Question 10

how do you reduce systematic error

Answer 10

• 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

Question 11

what is the definition of precision

Answer 11

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

Question 12

what is the definition of repeatability

Answer 12

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

Question 13

what is the definition of reproducibility

Answer 13

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 14

what is the definition of resolution

Answer 14

the smallest change in the quantity being measured that gives a recognizable change in reading

Question 15

what is the definition of accuracy

Answer 15

a measurement close to the true value is accurate

Question 16

what is the uncertainty of a measurement

Answer 16

is the bounds in which the accurate value can be expected to lie

Question 17

what is the absolute uncertainty

Answer 17

uncertainty given as a fixed quantity

Question 18

what is fractional uncertainty

Answer 18

uncertainty as a fraction of the measurement

Question 19

what is percentage uncertainty

Answer 19

uncertainty as a percentage of the measurement

Question 20

how do you reduce percentage and fractional uncertainty

Answer 20

you can measure larger quantities

Question 21

what is a readings

Answer 21

is when one value is found

Question 22

what is a measurement

Answer 22

when the difference between two readings is found

Question 23

what is the uncertainty in a reading

Answer 23

+/- half the smallest division

Question 24

what is the uncertainty in a measurement

Answer 24

at least +/-1 smallest division

Question 25

what is the uncertainty of digital readings and given values

Answer 25

have it quoted or assumed to be +/- the last significant digit

Question 26

what affects the uncertainty of the instrument

Answer 26

its resolution

Question 27

what is the uncertainty for repeated data

Answer 27

is half the range (mean +/- range/2)

Question 28

how can you reduce uncertainties

Answer 28

• by fixing one end as only the uncertainty in one reading is included
• or by measuring multiple instances

Question 29

should the uncertainties be given in the same number of sig figs as the data

Answer 29

yes

Question 30

when combining uncertainties if you add/subtract data what do you do with the uncertainties

Answer 30

you add the ABSOLUTE uncertainties

Question 31

when combining uncertainties if you multiply/divide data what do you do with the uncertainties

Answer 31

you add the PERCENTAGE uncertainties

Question 32

when combining uncertainties if your raising to a power what do you do with the uncertainties

Answer 32

you multiply percentage uncertainty by power

Question 33

how are uncertainties shown on graphs

Answer 33

as error bars

Question 34

what should the line of best fit go through

Answer 34

all error bars

Question 35

how can you find the uncertainty in a gradient

Answer 35

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

Question 36

what is the equation for percentage uncertainty in a gradient on a graph

Answer 36

= ((best gradient - worst gradient)/ best gradient) x 100

Question 37

if the best and worst lines have y intercepts what can you find from that

Answer 37

the (percentage) uncertainty of the y intercept using the same equation as the gradient

Question 38

what can be used on a graph to calculate the percentage uncertainty

Answer 38

the average of the two max and min lines max gradient-min gradient/2 x 100