Topic 1 : Measurement and Uncertainties Flashcards
Temperature SI Unit
Kelvin (K)
Distance SI Unit
Meters (m)
Current SI Unit
Ampere (A)
Time SI Unit
Second (s)
Amount of Substance SI Unit
Mole (mol)
Mass SI Unit
Kilogram (kg)
Light Intensity SI Unit
Candela (cd)
Derived quantities
- Derived quantities have units that are combinations of the fundamental units
- e.g. speed (m/s) or acceleration (m/s)
Analog measuring device vs Digital measuring device
analog measuring device is where you have to estimate last digit, somewhere between 2 digits whereas digital measuring device gives an exact last digit
Accuracy
how close an experimental value is to the true value
Uncertainty
used to estimate the likely ranges in which the true value will lie
Random error
- error due to the person measuring, rather than the instrument
- affects the precision of the reading
Random Uncertainties
- Random uncertainties/errors occur in any measured quantity
- The more measurements are taken, the closer the mean value of the measurements is likely to be to the “true” value of the quantity
- Taking repeat readings and calculating an average → reduces the effect of random uncertainties, improves the accuracy of the results
Parallax error
eye viewing meniscus at an angle rather than eye-level with the reading and perpendicular to the scale
Systematic error
- due to the instrument “out of adjustment” or poorly calibrated (e.g. voltmeter having a zero offset error or meter stick rounded on one end)
- affects the accuracy of the reading
- Taking repeats using the same method does not reduce systematic errors
Absolute error
raw uncertainty / precision of measurement → smallest unit of measurement of instrument
To calculate uncertainty for repeated measurements
absolute uncertainty = (max-min)/2
fractional error formula
fractional error = absolute error/measured value
percentage error formula
percentage error = (absolute error/measured value) * 100%
Calculating uncertainty in sum / difference
- To find the uncertainty in a sum, add the uncertainties of all the terms in the sum/difference
- If y = a±b, then Δy = Δa + Δb
Calculating uncertainty in product / quotient
- To find the uncertainty in a product or a fraction, add the percentage or fractional uncertainties of all the ingredients to find the total percentage or fractional uncertainty in the calculated value
- If y = (ab) / c, then Δy / y = Δa/a + Δb/b + Δc/c
Scalar
quantity that has only magnitude (size)
Vector
quantity with a magnitude (size) and a spatial direction
