measurements and errors

Question 1

SI units

Answer 1

fundamental units

Question 2

SI units made up of

Answer 2

mass - kg
length - m
time - secs
amount of substance - mol
temp - K
current - A

Question 3

how to find SI units of force

Answer 3

F = ma
= kg x m/s
= kgm/s

Question 4

larger prefixes

Answer 4

tera (T) 10^12
giga (G) 10^9
mega (M) 10^6
kilo (k) 10^3

Question 5

smaller prefixes

Answer 5

centi (c) 10^-2
mili (m) 10^-3
micro (u) 10^-6
nano (n) 10^-9
pico (p) 10^-12
femto (f) 10^-15

Question 6

random errors

Answer 6

affect precision - cause differences in measurements - causing spread around mean
CBAT VE REMOVED

Question 7

how to reduce random errors

Answer 7

• 3 repeats + mean
• use computers/data loggers to enable smaller intervals and reduce human error
• use appropriate equipment eg micrometer not meter rule

Question 8

systematic error

Answer 8

affect accuracy - occur due to faults in method or apparatus - cause results to be wrong by the same amount each time eg 2m too high
eg zero error, parallax error

Question 9

reducing systematic error

Answer 9

• calibrate apparatus by measuring a know value eg a 1kg weight
• remove background radiation in radiation experiments
• read the meniscus at eye level

Question 10

precision

Answer 10

how consistent the measurement are

Question 11

repeatability

Answer 11

if the original experimenter can redo with the same method / equipment and get the same results

Question 12

reproducibility

Answer 12

if the experiment is redone by a different person / technique / equipment- and same results are found its repeatable

Question 13

resolution

Answer 13

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

Question 14

accuracy

Answer 14

how close it is to the true value

Question 15

uncertainty

Answer 15

bounds in which the accurate value is expected to lie
can be:
absolute
fractional
percentage
- to reduce fractional and percentage- measure larger quantities

Question 16

reading vs measurement

Answer 16

• reading is where one value is found eg temp on a thermometer
• measurement is the difference between two readings eg length on a ruler

Question 17

uncertainty in reading/ measurements

Answer 17

• uncertainty in a reading is +- half the smallest division
• in a measurement is +-the smallest division

Question 18

digital readings - uncertainty

Answer 18

digital readings uncertainty is +- the last significant digit

Question 19

repeated data uncertainty

Answer 19

+- half the range
eg mean +- range/2

Question 20

reducing uncertainty

Answer 20

• fixing one end of a measurement
• measure multiple instances
  (given to the same sig figs as the data)

Question 21

adding / subtracting data and uncertainties

Answer 21

add absolute uncertainties

Question 22

multiplying/ dividing data and uncertainties

Answer 22

add percentage uncertainty
(percentage uncertainty = uncertainty / value x 100)

Question 23

raising data and uncertainties to a power

Answer 23

multiply % uncertainties by the power

Question 24

uncertainty in a graph

Answer 24

error bars
like if best fit should go through all of them

Question 25

uncertainty in a gradient

Answer 25

must go through ALL bars but you can draw the steepest and shallowest gradients (best and worst)
- uncertainty is the difference between the two/ best gradient x 100

Question 26

estimation

Answer 26

approximate values of physical quantities in order to make comparisons or to check if a value they’ve calculated is reasonable