UNITS There are 7 fundamental base units. All
Description: UNITS There are 7 fundamental base units. All other units can be derived from these units by multiplication or division of some combinations of the base units. Units can be simplified by using prefixes. These are the prefixes that you need
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slide1. UNITS There are 7 fundamental base units. All other units can be derived from these units by multiplication or division of some combinations of the base units. Units can be simplified by using prefixes. These are the prefixes that you need to be able to recognise and convert between at A – Level. UNIT 1 - MEASUREMENTS AND THEIR ERRORS You need to be able to convert between different units of the same quantity eg. When writing uncertainties always quote the uncertainty to the same number of decimal places are the value.
When calculating uncertainty in means leave answers in full, then find the uncertainty, then reduce the no. of decimal places of your value. Percentage uncertainty = absolute uncertainty x100
value When adding or subtracting measurements with uncertainties add the uncertainties.
When multiplying or dividing (or using indices) measurements with uncertainties add the percentage uncertainties.
When raising to a power multiply the percentage uncertainty by the power. UNCERTAINTIES
All measurements have an associated uncertainty. This reflects the errors involved in making the measurement. Fractional uncertainty = absolute uncertainty
value Reducing uncertainty practically – tips to remember:
If you are measuring a change in length, fixing one end of the scale reduce the percentage uncertainty as it means that only 2 readings need to be taken instead of 4.
Measuring something multiple times and dividing to find a value reduces percentage uncertainty as absolute uncertainty is unchanged but the value is larger. eg. Timing 10 oscillations to find period or measuring the thickness of 30 sheets to find the thickness of 1. GRAPHING UNCERTAINTIES
When plotting results onto a graph the uncertainties need to be taken into consideration. If the uncertainties could be visible on the graph (if they are significant) then the error bars must be drawn on the data points of the graph.
Two lines of ‘worst fit’ have to be drawn on graphs to estimate the magnitude of the error of the gradient. These are known as the maximum and minimum gradient. ORDERS OF MAGNITUDE
Common orders of magnitude:
Atomic size = 10-10 m
Frequency of visible light =
Wavelength of visible light = 10-7 m (Find using c=fλ)
Energy of a photon of UV light = 102 eV
Typical work function for Zinc = 4.31 eV
You will need to be able to use known equations to work out orders of magnitude for different quantities.<br>
When calculating uncertainty in means leave answers in full, then find the uncertainty, then reduce the no. of decimal places of your value. Percentage uncertainty = absolute uncertainty x100
value When adding or subtracting measurements with uncertainties add the uncertainties.
When multiplying or dividing (or using indices) measurements with uncertainties add the percentage uncertainties.
When raising to a power multiply the percentage uncertainty by the power. UNCERTAINTIES
All measurements have an associated uncertainty. This reflects the errors involved in making the measurement. Fractional uncertainty = absolute uncertainty
value Reducing uncertainty practically – tips to remember:
If you are measuring a change in length, fixing one end of the scale reduce the percentage uncertainty as it means that only 2 readings need to be taken instead of 4.
Measuring something multiple times and dividing to find a value reduces percentage uncertainty as absolute uncertainty is unchanged but the value is larger. eg. Timing 10 oscillations to find period or measuring the thickness of 30 sheets to find the thickness of 1. GRAPHING UNCERTAINTIES
When plotting results onto a graph the uncertainties need to be taken into consideration. If the uncertainties could be visible on the graph (if they are significant) then the error bars must be drawn on the data points of the graph.
Two lines of ‘worst fit’ have to be drawn on graphs to estimate the magnitude of the error of the gradient. These are known as the maximum and minimum gradient. ORDERS OF MAGNITUDE
Common orders of magnitude:
Atomic size = 10-10 m
Frequency of visible light =
Wavelength of visible light = 10-7 m (Find using c=fλ)
Energy of a photon of UV light = 102 eV
Typical work function for Zinc = 4.31 eV
You will need to be able to use known equations to work out orders of magnitude for different quantities.<br>