Measuring Internal Resistance - A Level Physics Practical
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- เผยแพร่เมื่อ 17 ก.ค. 2024
- A video demonstrating how we determine the internal resistance of a power supply using a simple model. Use of linear graph analysis, y=mx+c.
A Level Physics Practical Revision.
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Thank you.
It's really helpful
Thank you...
thank you for this!
Zoe Ubalde my pleasure! thanks for the thanks, made my day!
I've seen this practical with the voltmeter over resistor over the source of emf (cell/battery) and don't know which one is correct because of it being a potential divider between both resistors.
brilliant video! Can I just check when you were sliding the variable resistor, was it from max resistance to min resistance?
Yulin Chen yeah basically, you just need a good range for load resistance to get a good straight line graph. thanks for the comment.
THIS IS THE BEST VIDEO I EVER SEEN!! i been looking for measuring internal resistance video for like 2 hours, none of those video help. but after watch 5 mintues of your video, i understand how to calculate now! i just have 1 more question, from 3:00 why would you move your omhs to the left?
BlackMamba G69 wowzers! best ever! glad I could help out!
BlackMamba G69 not sure exactly what you mean, I move the slider to the left as it reduces resistance each time, I could have done the experiment the other way around and moved it to the right.
GorillaPhysics thanks for the reply, I already found out what happened :)
Hey thank you for the video it was helpful! I do have a question tho we've always learnt that when taking readings u must turn off the switch in between readings, is that correct?
Shahad Jabiti no problem, my pleasure. I've heard that too but I know from experience that you still get a precise line if you just leave it on as I did. The reason to turn it off if to avoid the heating effect of current, as the currents in this practical are so low the heating effect is pretty much negligible. However I've seen that advice on exam board material so I'd expect it would be an acceptable answer if asked to suggest an improvement to methodology.
The “r” in the circuits what does it stand for? I see u using a little wire thing but I don’t really know what it is? Thank you the video is very helpful
katy crazy Hiya. The little r stands for internal resistance. So a resistance that a power supply has.
This experiment is really just a model, as the real internal resistance is too small to measure accurately! So the little wire thing you mentioned is a fixed resistor. That's what we're measuring with our y intercept on the graph. Thanks! 😀
Hi! I don't really understand why the voltage decreases as current increases! It says in my textbook that the lost p.d. (which I think means p.d. lost from internal resistance ) increases as current increases.
ArmedPenguins you might be ready for the max power theorem!
th-cam.com/video/dF0EGP76EQ0/w-d-xo.html
Try to conceptualise the p.d. as energy per unit charge, this might help to explain the effect of a higher current causing more heating so higher resistance so dissipating more energy. I guess it depends on the proportional change in load resistance Vs internal resistance. There's lots going on in circuits!
Thanks for that vid! Our teacher did make us try using calculus but it was a little too difficult since we haven't seen chain rule and stuff yet. Okay so if the resistance increases due to the heating, shouldn't V increase? (from V =IR). Or, is this trying to say that as more p.d. is lost as internal resistance, less is lost from the load R, due to the ratio of how emf splits.
ArmedPenguins yeah exactly that. You've put it more clearly than I did. If the external resistors are ohmic then current shouldn't effect them. In this experiment with an ohmic resistor as the model of internal resistance then current shouldn't effect it either. Real power supplies do heat up though so that may be what your textbook is getting at... It's my best guess without having seen it! 😃
Thanks!
No dislike. Shows the importance of the video. Thanks
Sibasish Mukherjee thank you, glad you all have found it useful!
GorillaPhysics I shall thank you!
Is the conversion of milli amp to amp necessary?
Hiya! Yes, the gradient will be different if you don't convert. The y intercept will not change though, so if you just wanted to measure EMF you'd be ok!
Do you have a video for the experiment where you work out the viscosity of a fluid? (It's an AS edexcel practical) thanks
Anisha x Balls through washing-up liquid etc? I don't think I've done the practical. but I do have the theory. one sec....
th-cam.com/video/RDf_ULV42YQ/w-d-xo.html
+GorillaPhysics thanks for the reply, yes it is the washing liquid experiment.
Will AA cells work for experimenting??
Syed Aanjanul Haque yes! Should work just fine. I guess we buy the big ones because they'll last longer! 🦍
GorillaPhysics Thank you ! :D
for your reply
your first value was written wrong I believe
Yes you are right! the perils of reading and writing upside down! (Especially for 2 and 5 on a digital display!) You can easily spot that error on the graph though, so it wouldn't effect the line of best fit. One more reason why I like to have lots of data points in experiments.
Hopefully the video helped you understand the operatically though? Thanks for watching. :-)
+GorillaPhysics yep! loved the explanation :) thanks this will definitely help me in my upcoming exam !
+Lynette Art Great. I'll be doing a series of A Level practicals throughout the year so stay tuned!
+GorillaPhysics yes I will :)