Working as a physicist Flashcards
Femto
x10 ^-15
Pico
x10 ^-12
Nano
x10 ^-9
Micro
x10 ^-6
Milli
x10 ^-3
Kilo
x10 ^3
Mega
x10 ^6
Giga
x10 ^9
Tera
x10 ^12
What is uncertainty?
The interval in which the true value lies/the range of possible values
What is the error in a result?
The difference between the measured value and the true value
What is % uncertainty?
The uncertainty calculated as a percentage of the measured value
What is resolution?
The smallest measuring interval in a single reading. Resolution can give the uncertainty, but for instruments such as a stopwatch, human reaction time also contributes to uncertainty, so resolution cannot give uncertainty
What is the range?
The largest value minus the smallest value (in repeated readings)
What is precision?
Indicates the consistency between repeated values
Why is it better to measure larger values?
A larger value will give a much smaller percentage uncertainty, assuming the uncertainty is fixed
How should you estimate the uncertainty for a single measurement?
Given by half the smallest increment on the device. However, for instruments such as a ruler, the increment is the uncertainty, as 2 measurements are made.
How should you estimate the uncertainty for repeated readings?
Uncertainty is half the range, and % uncertainty is half range divided by mean
For calculated values, how should you combine uncertainties?
Add the % uncertainties (generally while multiplying or dividing results)
What is the purpose of error bars?
To visually represent the uncertainty, to allow a line of worst fit to be drawn which then allows for an uncertainty in the gradient to be calculated - difference between line of best fit and line of worst fit
What are the key steps of the scientific process?
- Creation and testing of theories
- Peer review
- Publication of results in scientific journals
- Testing of results by other scientists
- Acceptation of theory if supported by enough evidence
What are the 7 base quantities and their units?
- Mass (kg, kilogram)
- Length (m, metre)
- Time (s, seconds)
- Current (A, ampere)
- Temperature (K, kelvin)
- Amount of substance (mol, mole)
- Luminous intensity (cd, candela)
What are the most important things to consider when designing/evaluating an experiment?
- Does the method test what it set out to?
- Is the method clear enough?
- Are control variables properly controlled?
- Has appropriate apparatus been selected and will it be used correctly?
- Will enough repeated measurements be taken?
- Is the experiment safe?
- Are there any other ethical considerations?
How should you combine uncertainties when adding or subtracting data?
Add absolute uncertainties
How should you combine uncertainties when multiplying or dividing data?
Add the percentage uncertainties
How should you combine uncertainties when raising to a power?
Multiply percentage uncertainty by the power
What are systematic errors?
Errors that are the same every time an experiment is carried out, often caused by issues with the apparatus or the way the experiment is carried out. This includes zero errors.
Systematic errors affect the accuracy of the results, but not the precision, and can be identified when results are compared to another person’s, but are hard to see when considered in isolation.
To avoid them, check apparatus before and experiment begins
What are random errors?
Random errors vary and they are the cause of results being slightly different each time an experiment is repeated.
They are easier to spot than systematic errors and they affect the precision of results.
Using apparatus with better resolution can reduce the size of random errors in individual measurements, and doing more repeats then calculating an average also helps eliminate random error.
