Capacitors and Dielectrics 

Love the way he says "Farads"... dunno why... Keep up the good work Doc! Your videos are the best!

Thanks. You can find a complete list at the link on the graphic at the top of my main page.. The A level subjects are clearly identified. The rest are subjects which would be covered at some stage of an undergraduate course.

I'm afraid I have no idea. But I am reliably informed that if you Google how to download RU-vid videos to mobiles there is a substantial amount of help there. Just one small point. I understand that while my videos are clear on laptops, PCs and Ipads, the writing can be very small on the smaller mobile devices. Good luck.

This guy is absolute top class. I think he lectures at Kings College, which is a shame for me because I'm not a massive fan of London haha

Eminent guidance. Could you make a list of your lectures ordered by level (e.g. A.) and one by topics (e.g. Electronics, capacitor ; Electronics, inductor). It would be great to be able to download your notes for in depth analysis. You are splendid and precice - I love it!

Well there are far fewer free electrons in an insulator than in a conductor. But there are still some. So there is still scope for those free electrons to be attracted (or repelled) from a charge on the capacitor plate.

you sounded like Mr. Bean XD but, Thank you so much for everything.. this will really help me in the exam tomorrow. Kudos

Thanks. If it is where I think you mean I had already added an annotation to correct the error but I realise that not everyone can see the annotations.

this is beautiful, I would like to ask you kind sir to do a video on current orientation

Thanks for the explanation, much appreciated.

@DrPhysicsA Thank you very much for your great work. I am sorry, but i have to report a mistake. At about 9:15 there you write, that (1-b)=k. Actually it is (1-b)=1/k.

Time taken to fully charge a capacitor is taken to be about 5RC. So 300 = 5RC = 5 x C x 0.22 x 10^6 C = 300/ (5 x 0.22 x 10^6) = 2.7 x 10^-4 farad

C=Q/V. So as Q (charge) reduces (because current flows and current is charge per unit time) so does V - voltage or PD.

Not while the capacitor remains connected to the battery. Why would the PD across C be any different to that of the voltage of the battery. But if you disconnect the battery and then insert a dielectric or change the distance between the plates then the voltage can change. See 13:00

Thank you! It is very appreciated! ;)

Thank you so much!!!

Well then, if you take the copper plates off a charged capacitor a potential will still exist across the dielectric, and since there is a dielectric constant of space charge will flow to the charge dielectric from space (similar to how you stated charge will flow in dielectric even though the dielectric is not a conductor, for another video on how exactly that manifests). Of course same would apply if you were in earth’s atmosphere, or water, etc. just a different dielectric constant. It follows then for a charged capacitor that charge is not only stored in the dielectric but in the area outside of each plate.

thank you so much!!!

Ahhhh yeahh that makes sense now thanksss!!!!! :D

very helpful..thanks

Thankyou so much!! (:

Thank you.

awesome thanks

Dr physics thanks for the GREAT work you doing. pls how can I download your videos to my mobile device? I use blackberry bold 5.

how electron go through 2 capacitor series??

Sir, could you make a video on the effects on the parameters of capacitor, when dielectric is inserted with battery connected and battery not connected to the capacitor. Your parametrs could include capacitance, potential difference across capacitor, potential energy of the capacitor, charge on the plates, field in between the plates and the force on the plates due to each other.. Please it would be very useful to us... For example when battery is not connected, force will remain same or increase k times, etc. Your video just doesn't include effects on force on the plates of capacitor... Please include it in your video..

"There is not a large amount of free electrons to flow" in a dielectric? I'm sorry, what's happening is that the tiny particles that make up the dielectric are aligned and/or stretched to create tiny induced dipole moments, the sum of which is the surface charge on the dielectric, called a bound charge. There is no flow of charge inside the dielectric.

Isn't dielectric constant Er(kappa) and not E? What will be the capacitance for a parallel plate, in terms of epsilon, for air and for medium(dielectric)

@DrPhysicsA 1) A capacitor charges through a 0.22M ohm resistor. Calculate the capacitance if the time taken for it to reach full charge is 5 minutes. I keep getting 1.36 x 10^-3 :( but the answer is 2.7 x 10^-4 farad!! How do you do this?

at 6:09 it sort of looks like a resting neuron, just without the axon ending and cell body.

but the dielectric is an insulator, how is there going to be induction between the capacitor and thhe dielectric. charges dont move in non condducting materials right?

Okay thank you very much :)! Have you got videos on capacitor graphs and explaining why they have certain shapes? There was a question i attempted today and it gave u a graph of discharge for a torch(charge against time) and it said "explain why the output power from the LED decreases with time"? My guess was as a capacitor discharges the p.d across it falls hence charge will fall?

I mean in the video before this. Sorry i was writing the comment and it jumped to next video before it was done :)

oh yeah thanks btw

"feehh rahhts"

did u record the video with a calculator?

The formula for charging the capacitor is wrong. It should be a V instead of a 1.