Uncertainties in Graph Gradients and Y-Intercepts Using Lines of Worst Acceptable Fit

Methods for evaluating the reliability of your physics data and for quantifying the uncertainty in gradient and y-intercept values by using error bars, line of best fit and a line of worst acceptable fit.
You can practice these skills yourself with a worksheet I've created here (on TES):
www.tes.com/teaching-resource...
Or here (on TPT):
www.teacherspayteachers.com/P...
Relevant concepts: graphs, experimental uncertainties, gradients and intercepts, scatter of plots, line of best fit, line of worst acceptable fit, error bars, percentage difference, and percentage uncertainty.

[@aleezajehangir178]

Great video, thanks!

[@PhysicsHQ]

You're welcome!

[@aleezajehangir178]

@@PhysicsHQ Just keep uploading more videos like these 👍

[@PhysicsHQ]

I’ve got the follow up video for analysing log graphs coming soon.

[@annarae834]

Wow this explained everything so well!! Thank you so much for this video!

[@PhysicsHQ]

You’re welcome ☺️
All the best with your studies!

[@SGayanFernando]

This video helped me a lot! Thank you very much!

[@PhysicsHQ]

You're welcome! Glad it helped.

[@insertusername4822]

Thx alot, great video

[@naweyeeminn23]

May you please drop the link for the tips for not starting from the zero origin .

[@masked_musings]

really love this, very clear explanation. Is it possible to ask for the ppt you used? Would really appreciate it

[@PhysicsHQ]

Thanks very much!
It’s a Keynote presentation not PowerPoint. But yes I can share that via my website & TES. I’ll ping a link.

[@PhysicsHQ]

Hi again. Just uploaded it here as free download: wonkylogic.co/a-level-physics-hq
Will put it on TES too but on my website no login needed for download.

[@saieshengovender7109]

thanks a lot sir

[@PhysicsHQ]

Thanks! You’re welcome.

[@kidjuke6262]

clean presentation👌👌👌

[@PhysicsHQ]

Thanks. All the best with your studies.

[@taejgaul5991]

Thank you so much! 🥰 love the hair btw 😅

[@PhysicsHQ]

😊 thanks. I am at the mercy of what my hair does day to day!
All the best - especially if you have exams coming up.

[@Proph77]

How can I change the percentage to a definite value

[@PhysicsHQ]

The percentages are percentage uncertainties in gradient or intercept. They are related to a quantity of interest - e.g. resistivity (ρ) - so apply uncertainty calculation rules to determine percentage uncertainty in that quantity. Then multiply percentage uncertainty by the value of the quantity for the absolute uncertainty of the quantity.
E.G. gradient = ρ/A ⇒ %ρ = %gradient + %A
If ρ = 2.3 × 10⁻⁸ Ω m
And if %ρ was determined to be 5.8% then absolute uncertainty is 1 × 10⁻⁹ Ω m.
So the absolute uncertainty of the gradient or intercept is not of so much interest but the absolute uncertainty of the final value is of interest.

[@jamieashworth_]

Surely you should have a modulus sign on the bottom as if the gradient is negative you'll get a negative uncertainty

[@PhysicsHQ]

That’s right. A negative uncertainty wouldn’t make sense.

[@jamieashworth_]

@@PhysicsHQ okay was just saying because you didn't include a modulus on the bottom of your formula

[@PhysicsHQ]

Yes I see that now. Had forgotten at the time that the standard percentage difference equation needed modification.

[@eatinsomtin9984]

Does %c mean the the percentage uncertainty?

[@PhysicsHQ]

%c is the percentage uncertainty in the y-intercept.