1: Measurements and their Errors Flashcards
What are SI units?
The Fundamental (base) units
What are the 6 fundamental units?
Kilogram/Kg (mass), Amperes/A (electric current), Kelvin/C (temperature), Metres/m (length) , Time/s (time) and Moles/Mol (amount of substance).
What is a random error?
An error that affects precision and cannot be completely removed, it causes differences in measurements.
What is a systematic error?
An error that affects accuracy and occurs due to faults in equipment or experimental method, causing the result to be too large/small by the same amount each time.
What are 3 ways to reduce random error?
- take at least 3 repeats and calculate a mean
- use a computer or a data logger
- use higher resolution equipment
How can systematic error be reduced?
Calibrate apparatus before using.
What is precision?
Precise measurements are consistent, they fluctuate slightly about a mean value - this doesn’t indicate the value is accurate.
What is repeatability?
If the original experimenter can redo the experiment with the same equipment and method then get the same results - that is repeatable.
What is reproductibility?
If the experiment is redone by a different person or with different techniques and equipment and the same results are found, it is reproduceible.
What is the standard form for each prefix? Negative
c - x10^-1, d - x10^-2, m - x10^-3, m - x10^-6, n - x10^-9, p - x10^-12, f - x10^-15
What is resolution?
The smallest change in the quantity being measured that gives a recognisable change in reading.
What is an accurate value?
If the value is close to the true value.
What is absolute uncertainty?
uncertainty given as a fixed quantity.
What are the prefixes?
Tera/T, Giga/G, Mega/M, Kilo/k, Centi/c, Deci/d, Milli/m, Micro, Nano/n, Pico/p, Femto/f.
What is the standard form for each prefix? Positive
T - x10^12, G - x10^9, M - x10^6, k - x10^3
What is fractional uncertainty?
Absolute uncertainty / measured value
What is percentage uncertainty?
(absolute uncertainty / measured value) * 100
How do we combine uncertainties?
When adding and subtracting we add the absolute uncertainties together, when multiplying or dividing we add the percentage or fractional uncertainties. When rising to a power, we multiply the percentage uncertainty by the power.
What is an error bar?
The uncertainty shown on a graph. They show the absolute uncertainty.
Where does the ‘best’ line of best fit sit?
Passes close to the points as possible.
where does the ‘worst’ line of best fit sit?
either steepest or shallowest possible line that still goes through all the error bars.
How do we calculate the percentage uncertainty from the gradient?
(best gradient - worst gradient) / best gradient * 100
How do we calculate the percentage uncertainty from the y-intercept?
(best y-intercept - worst y-intercept) / best y-intercept x 100
What are the derived units?
Newtons/N, Joules/J, Pascals/Pa
How do you deduce Newtons?
Newtons =
Force = mass x acceleration
N = Kg x ms^-2
N = Kgms^-2
How do we convert J to eV (electronvolts)?
J –> eV = divide by 1.6 x10^-19
eV –> J = multiply by 1.6 x 10^-19
How to de convert J to kWh?
J –> kWh = divide by 3.6 x 10^6
kWh –> J = multiply by 3.6 x 10^6
1kWh = 3600kWs
3600kWs = 3,600,000Ws
3,600,000Ws = 3,600,000J = 3.6MJ
How do you find the uncertainty of a reading?
1/2 x resolution
How do you find the uncertainty of a measurement?
+/- smallest division
what is the uncertainty for repeated data?
range / 2
