{education} orders of magnitude + general formulae.

good afternoon everyone, today im going to be going over orders of magnitude for the people in their GCSE weeks. i had a physics test the other day that went really well except for on one of the questions it had me converting from metres to milimetres. sadly i hadnt expected to do that as i had studied nm (nanometres) μm (micrometres) and mm/cm's. so im just going to give you all a quick reminder on what = what. i recommend studying this as much as you study the 6 main formulae as it is incredibly likely that you will have to convert measurements and lengths in a gcse science exam.

what is the lowest measurement your expected to know?

the smallest measurement in length that you are expected to know is a micrometre (1×10⁻⁶ metre. thats a whopping millionth of a metre.) but dont worry, we will cover how to go from micrometres to mm's later in this extract.

what are the units we work with in physics GCSE?

in gcse physics we work with milimetres (MM), amperes (I), seconds (s), mol (Mol), kelvin (k), grams (g) and metres (m) these are what you are most likely going to be converting into.

what is 'mol'?

mol is a mole, more accurately it is the molar mass of a substance. this is usually used in chemistry but it can occasionally work its way into physics as well. it is calculated by using moles = mass / molar mass and is used to express the amount of a substance.

example calculation of moles (because moles are horrid little things)

Example question

    Let's say you have 60 grams of water (H₂O) and you want to find the number of moles.

        ‣ Determine the Mass: Determine the Mass: Mass of water = 60

        ‣ Find the Molar Mass of Water (H₂O):

                     ‣ Hydrogen (H) has an atomic mass of approximately 1.

                     ‣ Oxygen (O) has an atomic mass of approximately 16.

                     ‣ Therefore, the molar mass of water (H₂O) is 2 x 1 + 16 = 18 g/mol.

        ‣ moles = mass / molar mass = 60 / 18 gpmol ≈ 3.33 moles

general conversions you may need for physics (unrounded)

length

• 1 KM = 1e+6 mm
• 1 M = 1000 mm
• 1 CM = 10 mm
• 1 μm = 0.001 mm
• 1 nm = 1e-6 mm
• 1 mile = 1.609e+6 mm
• 1 yard = 914.20454544552 mm
• 1 foot = 304.73484848184000384 mm
• 1 inch = 25.394570706819994399 mm
• 1 nautical mile = 1851604.1318516000174 mm

volume

• 1 cubic inch = 16.38710000237962916 ml
• 1 cubic foot = 28316.908804111997597 ml
• 1 imperial teaspoon = 5.9194034719008641332 ml
• 1 imperial tablespoon = 17.758210414702588764 ml
• 1 imperial fluid ounce = 28.41312492349834784 ml
• 1 imperial cup = 284.13122423492853841 ml
• 1 imperial pint = 568.26249846996699944 ml
• 1 imperial quart = 1136.5249969399339989 ml
• 1 imperial gallon = 4546.0999877597359955 ml
• 1 litre = 1000.0021970000012743 ml
• 1 cubic metre = 1000002.1970000013243 ml
• 1 us teaspoon = 4.928930828837246203 ml
• 1 us tablespoon = 14.786797267772243458 ml
• 1 us fluid ounce = 29.573594535544486916 ml
• 1 us legal cup = 240.00052728000034108 ml
• 1 us liquid pint = 473.17751256871179066 ml
• 1 us liquid quart = 946.35502513742358133 ml
• 1 us liquid gallon = 3785.4201005496943253 ml

time

• 1 nanosecond = 1e-9 seconds
• 1 microsecond = 1e-6 seconds
• 1 millisecond = 0.001 seconds
• 1 minute = 60 seconds
• 1 hour = 3600 seconds
• 1 day = 86400 seconds
• 1 week = 604800 seconds
• 1 month = 2.628e+6 seconds
• 1 year = 31535965.4396976 seconds
• 1 decade = 315359654.39697599411 seconds
• 1 century = 3153596543.9697599411 seconds

temp

• 0 kelvin = -273.15 celcius
• 0 farrenheight = -17.7778 celcius

speed

• 1 knot = 1.68781 feet per second
• 1 killometre per hour = 0.911344 feet per second
• 1 metre per second = 3.28084 feet per second
• 1 mile per hour = 1.46667 feet per second

pressure

• 1 bar = 100000 pascal
• 1 pound per square inch = 6894.76 pascal
• 1 standard atmosphere = 101325 pascal
• 1 torr = 133.322 pascal

plane angle

• 1 radian = 57.2958 degrees
• 1 minute of arc = 0.0166667 degrees
• 1 milliradian = 0.0572958 degrees
• 1 gradian = 0.9 degrees
• 1 arcsecond = 0.000277778 degrees

mass

• 1 tonne = 1e+6 grams
• 1 kilo = 1000 grams
• 1 milligram = 0.001 grams
• 1 microgram = 1e-6 grams
• 1 imperial tonne = 1.016e+6 grams
• 1 us ton = 907185 grams
• 1 stone = 6350.29 grams
• 1 pound = 453.592 grams
• 1 ounce = 28.3495 grams

frequency

• 1 Khz = 28.3495 hertz
• 1 Mhz = 1e+6 hertz
• 1 Ghz = 1e+9 hertz

energy

• 1 kilojoule = 1000 joules
• 1 gram calorie = 4.184 joules
• 1 kilocalorie = 4184 joules
• 1 watt hour = 3600 joules
• 1 kilowatt hour = 3.6e+6 joules
• 1 electronvolt = 1.6022e-19 joules
• 1 british thermal unit = 1055.06 joules
• 1 us therm = 1.055e+8 joules 
• 1 foot-pound = 1.35582 joules

general

formulae needed

i dont feel good leaving you guys without telling you about the 6 essential formulae needed in physics, so im going to tell you what they are. im going to be telling you them where its AxB=C but it can go into the triangle of C on the the top and A and B beneath. this means that in the question if your trying to find something but you have two others, for example you want B but you have A and C, you can cover the one you need on the triangle and complete the question left (A/C).

1. E = Q x V
2. E = P x T
3. P = I x V
4. P = I^2 x R
5. Q = I x T
6. V = I x R

theres also an extra one thats usually given with the exam F = B x I x L (where B is teslas)

blog identifier: 042321-JDQIM