SI units Flashcards
What is a physical quantity?
A physical quantity is something that can be measured.
What needs to be done for any measurement + why?
For any measurement, the unit being used must be stated to give an understanding of the scale of the measurement.
In the case of measuring distance, why is it important to identify what measurement was used?
→ For example, distance can be measured in kilometres or in miles.
* They are similar, but not the same + it is important to identify which was used for the measurement, to know how far the distance actually is.
How are the units scientists use all over the world standardised?
The units that scientists use all over the world are standardised in the Système International d’Unités- SI units.
What is the Système International d’Unités?
Internationally agreed system of measurements.
What are the six fundamental(or ‘base’) units of measurement?
It is important to remember these six fundamental(or ‘base’) units of measurement:
* metre(m) - unit of length
* kilograms(kg) - unit of mass
* second(s) - unit of time
* amphere(A) - unit of electric current
* kelvin(K) - unit of temperature
* mole(mol) - unit of amount of substance
What are derived units + why are they not fundamental?
- There are many quantities scientists measure that come from fundemental units.
- These derived units are very useful to quote as measurements, but are not fundamental as they come from fundamental units.
Why is frequency not a fundamental unit, but a derived unit?
→ For example, frequency is the number of times something happens per unit of time.
* This is a useful quantity, but it is a division into the time unit.
* The standard unit for frequency is considering the number ‘per second’, which is called ‘hertz, Hz,’ from the fundamental unit ‘second’.
Examples of derived units, (their name, their unit + their abrrievitation)
Frequency, hertz, Hz
Force, newton, N
Energy, joule, J
Power, watt, W
Pressure, pascal, Pa
Electrical charge, coulomb, C
Electrical potential difference, volt, V
Electrical resistance, ohm, Ω
Magnetic flux density, tesla, T
