Units and Dimensions Flashcards
Name all the base units and their quantities
Length - m ‘the metre’
Second - s ‘the second’
Amount of substance - mol ‘The mole’
Electric current - A ‘The ampere’
Temperature - K ‘The kelvin’
Mass - Kg ‘The kilogram’
Example: What is the SI derived unit for speed?
- Definition: Speed is the measure of distance travelled over a period of time
Speed = Distance/time
IDENTIFY THE BASE UNITS
- Distance has the SI base unit of the metre/m.
Time has SI base unit of the second, s.
Speed = m/s Substitute base units into definition (equation)
- The SI derived unit for speed is therefore metres per second ms^-1.
Acceleration derived unit and name
ms^-2 don’t have one
Force derived unit and name
kgms^-2 Newton(N)
Pressure derived unit and name
kgm^-1s^-2 Pascal (Pa)
Energy derived unit and name
kgm^2s^-2 Joule (J)
Charge derived unit and name
A s Coulomb (C)
Potential difference derived unit and name
kgm^2A^-1s^-3 Volt (V)
Resistance derived unit and name
kgm^2A^-2s^-3 Ohm (Ω)
femto (f)
x10^-15
pico (p)
x10^-12
nano (n)
x10^-9
micro (μ)
x10^-6
milli (m)
x10^-3
centi (c)
x10^-2
deci (d)
x10^-1
kilo (k)
x10^3
mega (M)
x10^6
giga (G)
x10^9
tera (T)
x10^12
peta (P)
x10^15
How to convert from cm^2 to m^2
- Think about a simple example e.g. the area of a square with sides 1 cm (i.e. 0.01 m). 1 cm x 1 cm = 1 cm2; 0.01 m x 0.01 m = 0.0001 m2. Therefore 1 cm2= 0.0001 m2or 1x10-4 m2.
*Again think about a simple example e.g. the volume of a square with sides 1 mm (i.e. 0.001 m). 1 mm x 1 mm x 1 mm = 1 mm3; 0.001 m x 0.001 m x 0.001 m = 0.000000001 m3. Therefore 1 mm3= 0.000000001 m3or 1 x 10-9 m3.
How to convert from kmh^-1 to ms^-1
Yet again think about a simple example e.g. 1 kmh-1is 1000 m in 3600 s (i.e. 60 min x 60s). Therefore 1 kmh-1= 1000 / 3600 ms-1= 0.28 ms-1
How to convert from kWh to J
Joules are standard units of energy. However, electricity bills are given in kWh which are also units of energy. So 1 kWh is 1000 W for an hour. Using E = P x t gives E = 1000 x 3600 = 3600000 = 3.6 x 106 J. Therefore 1 kWh = 3.6 x 106 J.