02 Foundations of Physics Flashcards
physical quantity
property of an object or phenomenon that can be measured
International System of Units (SI)
standard system of units used by scientists which consists of 7 base units
6 base units used at A Level
metre (m)
kilogram (kg)
second (s)
ampere (A)
kelvin (K)
mole (mol)
degrees celsius to kelvin
add 273
prefix: peta
P
10^15
prefix: tera
T
10^12
prefix: giga
G
10^9
prefix: mega
M
10^6
prefix: kilo
k
10^3
prefix: deci
d
10^-1
prefix: centi
c
10^-2
prefix: milli
m
10^-3
prefix: micro
µ
10^-6
prefix: nano
n
10^-9
prefix: pico
p
10^-12
prefix: femto
f
10^-15
derived quantity
a quantity that comes from a combination of base units
derived unit
a unit used to represent a derived quantity
eg N for force
newton N in base units
kgms^-2
joule J in base units
kgm^2s^-2
how to find base units
use equations expressing derived quantities as base quantities and replace the quantities with the units (ignore any numeric values that do not have units eg 1/2 in Ek=1/2mv^2)
homogenous
identical
true value
value that would be obtained in an ideal measurement
(measurement) error
difference between a measured value and the true value of a quantity being measured
random error & how to correct
measurement errors where measurements vary unpredictably
cannot be corrected, but effect can be reduced by taking multiple measurements and calculating mean
systematic error & how to correct
measurements differ from true value by a consistent amount each time
find the value by which the measurements differ from the true value and add value to recorded measurements
zero error
type of systematic error: measuring device does not read zero when it should
accuracy
how close a measurement is to the true value - the closer, the more accurate
precision
how close repeated measurements are to each other - the closer, the more precise
uncertainty
an interval in which the true value of a measurement can be expected to lie
absolute uncertainty
+/- half the range
percentage uncertainty
(absolute uncertainty) / (mean value) * 100
adding / subtracting uncertainties
add the absolute uncertainties of each value
multiplying / dividing uncertainties
add percentage uncertainties of each value
raising uncertainties to a power
when a value is raised to n, percentage uncertainty is multiplied by n
resolution
smallest change a measuring instrument can detect
reading a micrometer
Read the sleeve measurement (resolution 0.5mm) then read the thimble measurement (resolution 0.01mm) and add the thimble measurement that aligns with the sleeve scale line to the sleeve measurement
reading a vernier caliper
read the cm value either lined up with (or if not lined up, to the left of) the zero line on the vernier scale. Them find the vernier scale line that best lines up with a line on the cm scale, and add this vernier scale measurement to the already attained cm measurement
