42 Physics Equations They Don't Tell You in A Level Exams

These are 42 of the most useful A Level Physics equations that they don't provide for you in the Data and Formulae Book in your exam.

I show my favourite equation for working out the area of a circle, then I go through all of the main topic areas including forces and motion, ideal gases, uncertainties, electricity, logs and finally waves.

I also found that because I set up my microphone in the wrong place, my initial audio quality sounded really bad - but I ran it through Adobe Podcast and it's new AI audio enhancer - it is amazing the difference!

Thanks for watching,

Lewis
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00:00 Introduction
01:19 Forces and Motion
06:20 Materials
08:37 Ideal Gases / Thermal
10:47 Uncertainty
14:16 Electricity
17:54 Capacitors
19:14 Logs
22:17 Waves

[AlanKey]

A = πd²/4

Mechanics
s = vt
s = vt - at²/2
KE = mv²/2
GPE = mgh
v = root(2gh)
v = root(2GM/r) [escape velocity]
W = mg
m1u1 + m2u2 = m1v1 + m2v2 [conservation of momentum]

Material Properties
EPE = kΔL²/2
stress = F/A
strain = ΔL/L
Young's Modulus = FL/AΔL

Thermal Physics
n = sample mass/relative molar mass
N = nN_A (where N_A = Avagodro's Constant)

Uncertainty
%uncertainty = absolute uncertainty/value × 100
absolute uncertainty = 1/2 range/mean
absolute uncertainty = |G_max - G_min|/2 [where G is gradient]
total absolute error if quantities are added (or subtracted) = sum of absolute errors
total % error if quantities are multiplied (or divided) = sum of % errors


Electricity
V1/V2 = R1/R2 [potential dividers]
v = root(2E/m) [velocity of accelerated charge]
qV = mv²/2
V = V_0 e^(-t/RC) [voltage across discharging capacitor]
V = (1 - V_0) e^(-t/RC) [voltage across charging capacitor]

[joelcairns]

Impressed at the effort that has gone into printing a backwards t-shirt so its the right way round!

[Fyr]

Its so useful to be able to derive some of these (equating circular motion with gravitational force to find Kepler's 3rd law or using coulombs law to derive other equations for charged particles like in a velocity selector, equating GPE with KE to find the equation for escape velocity, deriving the pV = (1/3)NMC^2 equation from the ideal gas model using conservation of momentum in an elastic collision and modelling 1/3 of particles travelling in each axis etc.)

[DynestiGTI]

Phase difference (rad) = 2π * path difference (m) / λ (m)

Constructive interference:
Path difference = nλ

Destructive interference:
Path difference = (n + 1/2)λ

[shahd]

you are an actual physics god thanks sir!

[eagle]

Absolutely Beautiful! You are amazing. I just want to ask 3 simple but very important questions to clear some confusion:
1 - When finding answers to certain degrees/figures, can we write our degree in the answer box next to the answer (e.g. N)
2 - Do you always give your answers to the same degree of figures as the values that they give you? I have been checking mark schemes and they sometimes give answers to different degrees.
3 - Does your answer always have to be EXACTLY like the mark scheme answer? Or is there a level of tolerance for every questions?

Thank you so much Physics digita...I mean Online!

[lustredream]

A small correction, for dicharging the capacitor, the equation for current should include a negative sign (I=-Ioe^-t/rc) since the polarity has changed. Other than that these are quite helpful, thank you!

[pratyasha]

11:02 was going to ask - takes a sheer amount of potential to write the other way around at that speed sir, quite admirable ahah - I was humbled real quick!!

[jameskonefal]

Another useful one when thinking about stationary waves is density (kgm^-3) = mass per unit length (kgm^-1) / cross-sectional area (m^2).

[spoonky]

thanks man, you should do a collaboration with science shorts, he is also insane at physics

[abdulqodirmir]

and also example or explanation of more usage of the formulae for the waves would be much appreciated (even a link to the related videos would be useful)

[peter_ade]

Another good one would be the equation for GPE in a radial field: Ep = - G M m / r

It isn't on the AQA equation sheet

[puggamerp]

Could you use instead +- 273.15 for converting between degrees and kelvin?

[kingzmash]

11:00 I have wanted to know this for CENTURIES 😅😂

[fahrenheit]

Pretty helpful, as usual. Is there a video on this channel going over uncertainties in more depth?
Also, I've got a q. I could've sworn I saw something somewhere which said the uncertainty in the gradient is the difference between the 2 worst fit lines divided by 2, and the same for any intercept. Is this also valid?
Also, I feel like the MS also said something about estimating the actual gradient as the average of the 2 worst fit lines (instead of eyeballing an actual best fit line ig). Is this fine, too?

[jw]

I have to say brightons scouts are next level

[abdulqodirmir]

A bit more explanation and example on this would be much appreciated:
%U=(half the range)/(mean value)

[pratyasha]

Sir which of the equations do we need to know how to derive? (Year 1 and 2 of OCR A-level Physics)?

[clytiec]

Not doing a levels yet, but that marker is so good

[MdNabilIslam-koui]

Could you please tell me that when do we use the reading furthest from the mean to calculate absolute uncertainty?