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Topic 1: measurements and uncertainties - Coggle Diagram
Topic 1: measurements and uncertainties
vectors and scalars
1.3 vector and scalar quantities
Scalar: A quantity which is defined by its magnitude only.
distance
speed
time
energy
Vector: A quantity which is defined by both is magnitude and direction.
displacement
velocity
acceleration
force
combination and resolution of vectors
Vector addition and subtraction can be done by the parallelogram method or the head to tail method. Vectors that form a closed polygon (cycle) add up to zero.
When resolving vectors in two directions, vectors can be resolved into a pair of perpendicular components. (triangle)
Definitions
Accuracy
: An indication of how close a measurement is to the accepted value (a measure of correctness)
Precision
: An indication of the agreement among a number of measurements made in the same way (a measure of exactness)
Random uncertainty
: An uncertainty produced by unknown and unpredictable variations in the experimental situation, such as temperature fluctuations and estimations when reading instruments. (Affects the precision of results - Can be reduced by taking repeated trials but not eliminated – shows up as error bars on a graph)
systematic error
: An error associated with a particular instrument or experimental technique that causes the measured value to be off by the same amount each time. (Affects the accuracy of results - Can be eliminated by fixing source of error – shows up as non-zero y-intercept on a graph)
Vector
: A quantity with both a magnitude ("size") and a direction
Scalar
: A quantity with magnitude ("size") only
1.1 Measurement in physics
fundamental and SI units
SI base units:
-length (m)
-time (s)
-mole (mol)
-electric current (A)
-temperature (K)
-luminious intensity, candela (cd)
-mass (Kg)
Derived units:
-frequency (Hz)
-force (N)
-pascal (Pa)
-energy (J)
-work (J)
-quantity of heat (J)
-power (W)
-electric charge (C)
-quantity of electricity (C)
-Potential Difference (V)
-electric resistance (ohm)
-Celsius temperature (°C)
-activity of a radioactive source(Bq)
scientific notation
number between 1 and 10 times x10^
metric multipliers:
Prefix
Peta
Tera
Giga
mega
kilo
hecto
deca
deci
centi
mili
micro
nano
pico
femto
abbreviation
P
T
G
M
k
h
da
d
c
m
µ
n
p
f
Value
10^15
10^12
10^9
10^6
10^3
10^2
10^1
10^-1
10^-2
10^-3
10^-6
10^-9
10^-12
10^-15
significant figures : always 3 sig figs
orders of magnitude
Estimations
are usually made to the nearest power of 10
1.2 uncertainties and errors
random errors:
-Caused by fluctuations in measurements centred around the true value (spread).
-Can be reduced by averaging over repeated measurements.
-Not caused by bias.
examples:
Fluctuations in room temperature
The noise in circuits
Human error
systematic errors:
Caused by fixed shifts in measurements away from the true value
Cannot be reduced by averaging over repeated measurements
Caused by bias
examples:
Equipment calibration error such as the zero offset error
Incorrect method of measurement
uncertainties:
error bars
uncertanty og gradient and intercepts