chapter 2 - prefixes and units - uncertainties

Question 1

prefixes (small)

Answer 1

femto (f) x 10-15
pico (p) x10 -12
nano (n) x 10 -9
micro (u)x10 -6
mili (m) x10 -3

Question 2

prefixes (big)

Answer 2

kilo (k) x 10 3
mega (M) x 10 6
giga (G) x10 9
terra (T) x10 12
peta (P) x10 15

Question 3

si

Answer 3

standard system of units

Question 4

base units

Answer 4

all units can be expressed as these
meters
seconds
kg
amps
kelvin
moles
candela (luminosity)

Question 5

how to convert SI > base units

Answer 5

use a simple GCSE equation and substitute in units eg
Q = It
C = As

Question 6

homogeneity in equations

Answer 6

in an equation the units on both sides must be the same - write equation and insert in units
eg s = ut + 1/2at^2
m = ms^-1 x s + ms^-2 x s^2
m = m + m

Question 7

random error

Answer 7

vary due to unpredictable circumstances
cannot be corrected only mitigated - make more measurements and calculate new mean

Question 8

systematic error

Answer 8

differ from true value by a consistent amount
corrected by using a different technique to take measurements

Question 9

precision

Answer 9

how close they are to each other/ the mean

Question 10

accuracy

Answer 10

how close they are to the true value

Question 11

repeatable

Answer 11

can be repeated using the same method to get the same results

Question 12

reproducible

Answer 12

can be repeated using different equipment or techniques and the same results are obtained

Question 13

resolution

Answer 13

smallest division on measuring apparatus

Question 14

uncertainty in one measurement

Answer 14

+- resolution (1sf)
eg 2.7 +- 0.1

Question 15

uncertainty in repeated measurements

Answer 15

+- 1/2range
eg 1.9, 1.95 and 2 uncertainty is +- 0.05

Question 16

uncertainty when multiplied by a number

Answer 16

multiply uncertainty too
eg 1.2 +- 0.4 (/4) = 0.3 +- 0.1

Question 17

uncertainty when performing a function eg sin/ log

Answer 17

do 1/2(max-min)
eg 2.6 +-0.2 logged
uncertainty is (log(2.8) - log(2.4))/2 = 0.03

Question 18

combining uncertaincies

Answer 18

if added/ subtracted ADD uncertainties

Question 19

percentage uncertainty

Answer 19

uncertainty/ quantity measured x 100

Question 20

how to reduce percentage uncertainty

Answer 20

measure over larger amounts

Question 21

percentage uncertainty when raised to a power

Answer 21

x %uncertainty by the power

Question 22

percentage uncertainty if times or divided

Answer 22

ADD percentage uncertainty

Question 23

how to get absolute uncertainty from percentage uncertainty

Answer 23

find the percentage of the measurement
eg percentage uncertainty of 100 is 1% so uncertainty is 0.01 x100 = +-1

Question 24

when combining absolute and percentage uncertainties

Answer 24

deal with absolute first then add %uncertaincy

Question 25

absolute uncertainty on a graph

Answer 25

use error bars (+- smallest division or 1/2 range)
- draw WFL

Question 26

experimental uncertainty

Answer 26

+- (WFL value - BFL value)