This section has information on the system of units used by the Scottish Qualifications Authority, (SQA). The SQA uses the Systéme Internationale (SI) for units of physical quantities.
This international system of units is based on the following five units:
Other SI units are defined in terms of these basic units.
SQA has published a list of the physical quantities in Higher Physics, together with the symbol and SI unit of each quantity - click on the link to see the list.
Learn these quantities, symbols and units a few at a time so that by the time you sit your Higher you will know all of them.
You also need to know the following prefixes:
Table of units
|G||Giga||109||one thousand million|
|n||nano||10-9||one thousandth of a millionth|
|p||pico||10-12||one millionth of a millionth|
Each prefix can go before any SI unit. For example:
Table of units
|1 pF||= 1 picofarad||= 1 × 10-12 farads||= 1 × 10-12 F|
|1 ns||= 1 nanosecond||= 1 × 10-9 seconds||= 1 × 10-9 s|
|1 µm||= 1 micrometre||= 1 × 10-6 metres||= 1 × 10-6 m|
|1 mA||= 1 milliamp||= 1 × 10-3 amps||= 1 × 10-3 A|
|1 kV||= 1 kilovolt||= 1 × 103 volts||= 1 × 103 V|
|1 MJ||= 1 megajoule||= 1 × 106 joules||= 1 x 106 J|
|1 GHz||= 1 gigahertz||= 1 × 109 hertz||= 1 × 109 Hz|
When you are trying numerical problems always make sure that you use the SI unit of each quantity given - this guarantees that the quantity you are calculating will be in its SI unit.
The kilogram is the SI unit for mass - do not change kilograms to grams.
Data can be obtained by taking measurements, and can lead to an explanation of why materials have different properties. During an experiment other factors, which could affect the outcome, need to be controlled.
Accuracy and reliability of data
Many people may have ideas about why materials have different properties, but these opinions are not very useful if they are not supported by data. To justify an explanation, you need to have data to support it. This data may be obtained by taking measurements.
The table below shows the length that equal-sized samples of one type of rubber can be stretched before they break:
Length of rubber before breaking (mm)
The accuracy of each measurement depends on the quality of the measuring apparatus and the skill of the scientists taking the measurement. If the apparatus is faulty, or the scientists make a mistake, the measurement may be inaccurate.
For the data to be reliable, the variation within the values must be small. There is always some variation in any set of measurements, whatever is being measured. There may be small differences in the composition of the rubber or the way the measuring apparatus is used.
In this set of data, each measurement is only slightly different from the others. The results are repeatable, meaning that each time a measurement is taken it has approximately the same value. We can say that this set of data is reliable.
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