M2 Units, Measurement and Errors Flashcards
define quantity
implies a measurement of something and its units
what are the six basic quantities and their unit
Mass - kg Time - s Current - A Temperature - K Length - m Amount of substance - mol
what is deci to the power of and what’s its symbol
-1
d
what is centi to the power of and what’s its symbol
-2
c
what is milli to the power of and what’s its symbol
-3
m
what is micro to the power of and what’s its symbol
-6
weird u
what is nano to the power of and what’s its symbol
-9
n
what is pico to the power of and what’s its symbol
-12
p
what is femto to the power of and what’s its symbol
-15
f
what is kilo to the power of and what’s its symbol
3
k
what is mega to the power of and what’s its symbol
6
M
what is giga to the power of and what’s its symbol
9
G
what is tera to the power of and what’s its symbol
12
T
what’s the difference between accuracy and precision
accuracy describes the difference between the measurement and the actual value whereas precision describes how close to each other repeated measurements are
how do you measure off a vernier calliper
look at the zero of a vernier scale and read where this comes on the main scale, estimating the figure for tenths of a millimetre
look along the vernier scale to see what vernier division coincides with one of the divisions on the main scale - this gives the correct figure for tenths of a millimetre
how do you measure off a micrometre screw gauge
read the main scale, estimating the figure for tenths of a millimetre
read the scale on the sleeve
what is more accurate, a vernier calliper or a micrometre
micrometer
the possible error associated with an instrument is always taken as…
+ or - the smallest scale division
what is the error or uncertainty of a metre stick
+ or - 1mm
what is the error or uncertainty of a vernier calliper
+ or - 0.1mm
what is the error or uncertainty of a micrometer screw gauge
+ or - 0.01 mm
how do you work out percentage error
(error / measurement) X 100
how do you combine errors when adding or subtracting quantities
add errors
how do you combine errors when multiplying or dividing quantities
add percentage errors
how do you combine errors when raising to a power
multiply the percentage error by the power
what is a zero error
caused when an instrument is not properly calibrated so it gives a non-zero value when the true value is zero
what is a systematic error
caused by inaccuracy in the apparatus or its
use by the person conducting the experiment. Shifts all the measurements in the same direction.
what is a random error
causes measurements to be scattered above
and below the true value when repeated. Better results can be obtained by finding a mean value of several results.
what’s an absolute uncertainty
the total uncertainty of the measurement
what’s a percentage uncertainty
the uncertainty as a percentage of the measurement
If I measure the time as 5.25 ± 0.01 s then what is the
percentage error in the measurement?
% 𝐄𝐫𝐫𝐨𝐫 =
𝟎.𝟎𝟏/𝟓.𝟐𝟓
× 𝟏𝟎𝟎 = 𝟎. 𝟐%
If the extension of a spring is (5.1 ± 0.3 cm) – (2.0 ± 0.1 cm) then what is the extension?
(5.1 – 2.0) ± (0.3 + 0.1) cm = 3.1 ± 0.4 s
How do you work out the gradient
∆y / ∆x
equation of a straight line
y = mx + c
estimate:
i) mass of a person
ii) mass of a car
iii) height of a man
iv) walking speed
i) 70kg
ii) 1500kg
iii) 1.8 m
iv) 1.5ms^-1
what is meant by homogeneity of units
the units in any equation must be equal on both sides
what is pd in base units
kgm^2s^-3A^-1
