Capacitor Discharge Practical - A Level Physics Key Practical - Experimental Physics Revision

In this practical I show you how to conduct and refine a practical into the discharge of a capacitor. This is specified as a core practical in many A Level Physics Syllabus.
It is an important practical and involves many key and transferable practical skills for your practical skills paper, general and practical principals of physics paper.
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[@spag5296]

Using a very high resistance should slow down the decay of the voltage, so its easier to read off values on the voltmeter. Great experiment otherwise!

[@idontcare8756]

Thank you

[@nevinneblake8254]

Is a capacitor of 3000microfarad store more charge than one with 600 microfarad

[@antony5899]

thank you mate 🐐

[@KitBetts-Masters]

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[@janeb9986]

So how do we find charge at each time interval? I want to plot a graph of charge versus time to prove that charge of a capacitor decays exponentially during discharge.

[@martians_sol2568]

i have my unit 6 exam (my last a level ever!) tomorrow and your core practical vids have been super helpful, thank you!!

[@suryavanshnagpal]

What does the gradient of the V-t graph show??

[@KitBetts-Masters]

Rate of discharge. Proportional to rate of energy transfer... so power output.

[@fredrickwamai1006]

Really helpful clip. Still useful in 2021, even with Corona pandemic upon us!!

[@spencerpostlethwaite1346]

CPAC still has to be done 🤣

[@emmanuelb3081]

W physics teacher

[@richardkenny6290]

What capacity capacitor are you using? Is there a minimum capacitance that must be used?

[@KitBetts-Masters]

100micro Farads. There is no minimum, but the smaller the value of R and C the quicker the discharge. Smaller times are less easy to measure, so just pick a value of RC that gives you a time for discharge that you can measure accurately. Thanks,

[@richardkenny6290]

@@KitBetts-Masters Thank you for the reply! I am having trouble getting the lab to work unless I use a 1F capacitor. Maybe for the smaller capacitors (like 100 microF) I need to use a larger resistor to increase the discharge time. It seems that the capacitor is discharging almost instantly. I will try using larger resistor. Thank you!

[@richardmortimer6539]

@@richardkenny6290 The time constant is the product of capacitance (in uF) and resistance in Ohms and needs to be comparable to the timescale for your measurement. Eh, 470 uF and 100kOhm gives a time constant of 47 s, so either charging or discharging you should be able to obtain reasonable sets of data.

[@azmilard]

thank you so much this have helped me understand more about capacitors

[@KitBetts-Masters]

Great news! Very glad to help! 🦍

[@leeboehmer6793]

Really helpful video, man. Thanks.

[@KitBetts-Masters]

Glad to help my buddy. I hope you'll scan my channel for my other useful content. And recommending to your friends and teachers is another big help!

[@Jet2Guy]

hi whats the y=mx+c form for the charging equation?

[@Vipa567]

Is it possible to get the half life of the capacitor from time constant?

[@KitBetts-Masters]

Malazan yeah, half life would be RCxln2

[@KitBetts-Masters]

Think of RC as being the same as 1/lamda in nuclear decay.

[@Vipa567]

The question is, "With R set to zero resistance, charge the capacitor by connecting the flying lead to terminal C. Discharge the capacitor by connecting the flying lead to terminal D. Make suitable measurements to determine T(o), the time for the voltmeter reading to decrease by 50% when R=0." This is for half life?

[@KitBetts-Masters]

Malazan must be some confusion as if there is R=0 then maths can't work. Double check the question is there another resistance that you need to take account of? Clearly if R=0 then RCxln2 is 0 or the exponent is t/0 which is meaningless.

[@Vipa567]

In the practical there were 3 resistors and a hidden one. I made another graph besides the onew in this vid of all 3 resistor combinations and found the resistor by following the line of best fit beyond y=0 to where it hits the x-axis. In the papers its written "Hint: you have probably not drawn your graph with a true origin, even if you think R=0."

[@anujtalwar]

Sir which university do you teach at?

[@KitBetts-Masters]

Lols, secondary school bud. GCSEs and A Levels! (15-18 year olds.)

[@mushfek]

Nice graph!

[@KitBetts-Masters]

Thanks, it doesn't get more exciting than graph time!