# Physics - Units and Prefixes

> Source: https://ollybritton.com/notes/a-level/physics/topics/units-and-prefixes/ · Updated: 2020-09-07 · Tags: ankify, physics, year-1

# Units and Prefixes
Units and Prefixes are a simple topic but very important and foundational for the rest of physics as a whole. It's one of those things that are important learning because it improves fluency in thought involving physics problems and having a good conceptual understanding of what the units actually represent can also be helpful.

## Units
##### What are the two types of units??
* Base units
* Compound units

##### What is a base unit??
Standard units of measurement from which all other SI units are derived.

##### What is a compound unit??
An SI unit created from a combination of base units.

##### What are the 6 base units??
* metre
* kilogram
* second
* Ampere
* Kelvin
* Mole

##### How do base units relate to base quantities??
Base units are standard units of measurement for the base quantities.

##### What are the 6 base quantities??
* length
* mass
* time
* electric current
* absolute temperature
* amount of substance

##### What is the base unit of mass??
kilogram, [$]kg[/$]

##### What is the base unit of length??
metre, [$]m[/$]

##### What is the base unit of time??
second, [$]s[/$]

##### What is the base unit of current??
ampere, [$]A[/$]

##### What is the base unit of temperature??
kelvin, [$]K[/$]

##### What is the SI unit of potential difference??
volt, [$]V[/$]

##### What is the SI unit of density??
kilogram per metre cubed, [$]kgm^{-3}[/$]

##### What is the SI unit of energy??
joule, [$]J[/$]

##### What is the SI unit of power??
watt, [$]W[/$]

##### What is the SI unit of charge??
coloumb, [$]C[/$]

##### Q: What is [$]1m^2[/$] in [$]mm^2[/$]??
[$]10^6mm^2[/$]

##### Q: What is [$]1m^3[/$] in [$]cm^3[/$]??
[$]10^6cm^3[/$]

##### Q: What is [$]1km^2[/$] in [$]m^2[/$]??
[$]10^6m^2[/$]

##### Q: What is [$]1cm^3[/$] in [$]mm^3[/$]??
[$]10^3mm^3[/$]

##### Q: There are [$]10^24[/$] free charge carriers per [$]m^3[/$] of material. How many are there per [$]mm^3[/$]??
[$]10^15[/$]

##### Q: [$]10^6[/$] particles strike each [$]mm^2[/$] of a surface per second. How many strike [$]1m^2[/$] of the surface per second??
[$]10^12[/$]

##### Q: If there is 1 particle per [$]mm^2[/$], how many are there per [$]m^3[/$]??
[$]10^9[/$]

##### Q: Water has a density of [$]1000kgm^-3[/$]. What is this in [$]kgcm^{-3}[/$]??
[$]10^{-3}[/$]

##### Q: Water has a density of [$]1000kgm^-3[/$]. What is this in [$]gcm^{-3}[/$]??
[$]1[/$]

## Units
##### What is the value of the prefix T (tera)??
[$]10^12[/$]

##### What is the prefix for [$]10^12[/$]??
T, tera

##### What is the value of the prefix G (giga)??
[$]10^9[/$]

##### What is the prefix for [$]10^9[/$]??
G, giga

##### What is the value of the prefix M (mega)??
[$]10^6[/$]

##### What is the prefix for [$]10^6[/$]??
M, mega

##### What is the value of the prefix k (kilo)??
[$]10^3[/$]

##### What is the prefix for [$]10^3[/$]??
k, kilo

##### What is the value of the prefix d (deci)??
[$]10^{-1}[/$]

##### What is the prefix for [$]10^{-1}[/$]??
d, deci

##### What is the value of the prefix c (centi)??
[$]10^{-2}[/$]

##### What is the prefix for [$]10^{-2}[/$]??
c, centi

##### What is the value of the prefix m (milli)??
[$]10^{-3}[/$]

##### What is the prefix for [$]10^{-3}[/$]??
m, milli

##### What is the value of the prefix [$]\mu[/$] (micro)??
[$]10^{-6}[/$]

##### What is the prefix for [$]10^{-6}[/$]??
[$]\mu[/$], micro

##### What is the value of the prefix n (nano)??
[$]10^{-9}[/$]

##### What is the prefix for [$]10^{-9}[\$]??
n, nano

##### What is the value of the prefix p (pico)??
[$]10^{-12}[/$]

##### What is the prefix for [$]10^{-12}[/$]??
p, pico

##### What is the first step in using a variable with a prefix??
* Replacing the prefix symbol with its equivalent multiplier.
* e.g. [$]0.16\muA = 0.16 \times 10^{-6}A[/$]

##### Q: What is [$]1.4kW[/$] _without_ a prefix??
[$]1.4\times10^3 W[/$]

##### Q: What is [$]340MW[/$] _without_ a prefix??
[$]3.4\times10^8 W[/$]

##### Q: What is [$]46pF[/$] _without_ a prefix??
[$]4.6\times10^{-11}[/$]

##### Q: What is [$]6.4\times10^{-3}[/$] _with_ a prefix??
[$]6.4mW[/$]

##### Q: What is [$]0.520\times10^4 \ohm[/$] _with_ a prefix??
[$]5.2k\ohm[/$]

##### How many $cm^3$ in $1\quad\text{litre}$??
$$
1000cm^3
$$

##### How many $m^3$ in $1\quad\text{litre}$??
$$
10^{-3}m^3
$$

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