Topic 1: Measurements and uncertainties Flashcards
What is precision?
how well repeated measurements of a value agree with one another (exact)
What is accuracy?
how well a measurement agrees with the true value (correct)
When using an analog scale, what is the uncertainty?
plus or minus half the smallest scale division
When using a digital scale, what is the uncertainty?
plus or minus the smallest unit shown
When taking repeated measurement how do you find the uncertainty?
find the difference between the average and the measurement that is furthest from the average
What is the order of magnitude for the size of subatomic particles to the extent of the visible universe?
10^-15 m to 10^25 m
What is the order of magnitude for the mass of the electron to the mass of the universe?
10^-30 kg to 10^50 kg
What is the order of magnitude for time for light to cross a nucleus to the age of the Universe?
10^-23 s to 10^18 s
What is the order of magnitude for the size of a hydrogen atom?
10^-10 m
What is the order of magnitude for the size of a proton?
10^-15 m
What is the ratio of diameter of a hydrogen atom to its nucleus?
10^-10/10^-15 = 10^5
What is displacement?
the distance moved in a stated direction (the distance and direction from the starting point)
What is velocity?
the rate of change of displacement
What is acceleration?
the rate of change of velocity
What is instantaneous speed/velocity?
the change in distance/displacement divided by time at one particular time
What is a frame of reference?
a point from which a situation is observed
What are systematic errors and examples of them?
Systematic errors are constant errors that are due to faults in the system used to measure a variable.
Examples are miscalibration, wearing down over time, or a constant delay in every reading.
They will be precise but not accurate.
What are random errors and examples of them?
Random errors can occur in any method of measuring but happen primarily when estimating.
These will differ from trial to trial and are not precise.
For example, measuring the speed of sound when making a loud clap a distance from the wall might cause a random error due to the reaction time of the experimenters measuring the time it takes the sound to travel.
What are absolute uncertainties?
When the uncertainty is given in the same unit as the answer given and should be written to the same number of decimal places.
E.g. 294.56 ± 3.01 N
What are fractional uncertainties?
When the uncertainty is given as a fraction of the original quantity. It is dimensionless (without units).
E.g. 2.6 ± 0.2 = 2.6 ± (0.2/2.6 or 0.077)
What are percentage uncertainties?
When the uncertainty is given as a percentage of the original quantity. You can get this from multiplying the fractional uncertainty by 100.
E.g. 2.6 ± 0.2 = 2.6 ± 7.7%
What is the combination of the uncertainties of different quantities called?
Propagation of uncertainties
What do you do to the uncertainty of two values when you multiply or divide them?
You add their fractional or percentage uncertainties.
