Physics - Units and Prefixes
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 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 SI unit of density?
kilogram per metre cubed, [$]kgm^{-3}[/$]
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 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 [$]0.520\times10^4 \ohm[/$] _ with _ a prefix?
[$]5.2k\ohm[/$]