Charge and Mass of an Electron - A Level Physics

[@Darcmora]

Ive been watching multiple physics videos the past couple of days, and I have to say your diagrams and explanations were by far the best and easiest to understand. Thank you!

[@DrPhysicsA]

Thanks. I am delighted. I hope you get a real good grade. No remuneration is necessary. Feedback like yours makes it all worthwhile.

[@DrPhysicsA]

The Millikan's Oil drop experiment requires two sets of balancing forces. First the oil drop achieves terminal velocity which means the gravitational force down is balanced by the viscous drag force up. This enables us to calculate the mass of the oil drop. Secondly an electric field is applied to stop the drop from falling. At that point there is no viscous drag. Instead the gravitational force down is balanced by the electric field force up. This enables the charge on the drop to be calculated

[@rahilashah71]

Thank you sir! Id also just like to say that you are so much better to listen to that all the other teachers I've come across on here! It makes it that much more easier to learn, so thank you :)

[@DrPhysicsA]

Thanks. Let me know if there's anything at AS level I have missed in the series that you think might help you and your fellow students.

[@DrPhysicsA]

Go to my main page and scroll down to see two videos on Fluid Dynamics covering Archimedes Principle. Bernoulli's Theorem (which you may not need) and Stokes' Law.

[@DrPhysicsA]

I think so. It is the exam taken in the UK by students aged 17-18 just before they go on to university. I hope it covers broadly the same material as that covered by students elsewhere in the world of about that age.

[@isaacalawode7035]

I have my final A Level physics exam on Thursday (AQA unit 5) I want to thank you very much for these videos. This one especially as it has helped me soo much to understand the concepts for the option topic :)

[@DrPhysicsA]

The charged particle has to be moving to start with. A stationary charged particle in a mag field wont move. But if is it moving with velocity v thro a mag field B, then there will be a force perpendicular to the plane of v and B. That's a condition for circular motion.

[@DrPhysicsA]

Thanks. Very kind of you to say so.

[@李溟东]

Thank u so much! I am an international student and I was really confused with Millikan's oil-drop experiment. But now I am quite happy with it and I found it is not as difficult as my imagination! Thank u so much!!

[@gregorycawthorne]

I haven't done this yet as I'm only doing AS at the moment, but still very interesting thank you! I shall revisit next year! *Subscribed*

[@DrPhysicsA]

Good question. HIghly unlikely he would have got any drops with just one electron charge on them. So I guess numerous observations had the electron charge as the highest common factor.

[@aryan0605]

really a great job sir...... Have my A level exam in 3 days its really helpful for quick revision

[@DrPhysicsA]

Because you stop the particle so that the mag and electric forces are equal. If no movement, no viscous drag.

[@AnotherFkingidiot]

These videos are awesome for my year 12 HSC revision! I'm curious, what exactly is "A level physics"? is that like the UK version of high school finals?

[@jad2805able]

Great work. You really explain it clearly, making it very understandable for me ^^

[@deeyabheeroo8945]

Sir, for the millikan's experiment, why is upthrust not considered?

[@feelingzhakkaas]

Very nice and effective video. How the Neutrons were discovered ? Do you have video on this? Thanks for updating our knowledge.

[@samiurai0]

Best Physics teacher ever.

[@paulhong111]

why do the electrons act like a magnetic monopole (S) at the JJ Thomson experiment ? If you apply a magnet around the tube from the outside without an external electric field, the beam ray deflects towards the N-pole and repels the S-pole. From the Stern-Gerlach experiment, an electron has a magnetic dipole moment. So it could have N-pole as well. But it seems that the electrons on the Thomson experiment don't have the N-pole. Why is that ? Thanks

[@DrPhysicsA]

F=Bqv which supplies centripetal force = mv^2/r Bqv=mv^2/r Bqr=mv So r = mv/Bq

[@DrPhysicsA]

The electron is moving to the right but the conventional current moves from + to - so it is moving to the left.

[@awolgeordie9926]

Thank you very much for these excellent videos. My A Level Physics students enjoy them very much here in Thailand. They were wondering though .... is your paper infinitely long??

[@DrPhysicsA]

+AWOL Geordie Many thanks. Glad they are of help. The paper is in fact only A3.

[@李溟东]

It is perfectly clear and logical!

[@alphie10]

brilliantly explained. Milikan was a clever guy but how did he figure out the "multiplier" and the "number" 1.6 x 10^-19 C did he just record patterns and read of values from what he used to measure the charge on the oil droplet.

[@DrPhysicsA]

The mathematics will show that when you have an electron moving from west to east in a force operating from north to south the electron will follow a curved rather than the straight path.

[@mahmoudm451]

How did Thomson observe a the positive particles slightly diverting towards the negative plate? I thought that the cathode at high temperatures only releases electrons and not protons? and why did he add hydrogen to the tube? how did that help him? is it that the electrons from the cathode were ionizing the hydrogen atoms and causing them to become positively charged? is it the positively charged hydrogen atom that is diverting towards the negative plate? please answer.

[@saminatariq561]

Mahmoud Matar and why were those positive particles moving towards anode? It's all confusing

[@nineeleven9455]

What makes you think there are any particles at all moving through the tube.? There is no evidence of such. It's all electromagnetic phenomena.

[@DrPhysicsA]

That assumes that the formula at 13:39 has E=V/r

[@aishilaha5311]

THANK YOU SIR, I AM OF CL X STANDARD AND KNOW MUCH LESS IN THE OCEAN OF PHYSICS BUT I HAVE SOME QUESTIONS 1-WHY IS THE ELECTRON GETTING ATTRACTED IN A PARABOLIC PATH AND NOT IN A STRAIGHT PATH IN THE EVACUATED TUBE 2- WHAT IS THE EFFECT/IMPORTANCE OF HYDROGEN 3 - IF THE ELECTROS ARE GETTING DEVIATED AND ARE BEING ATTRACTED, THEN THE ACTUAL CIRCUIT BREAKS AND THEN NO ELECTRONS WILL BE PRODUCED- IS IT SO? (I FOUND DIFFICULT TO UNDERSTAND THE LATER PART ON CALCULATIONS WHICH I WILL TRY LATER)

[@SailaMaham]

That was really really helpful. Thank you so much!

[@Yizak]

And of course from e/m you can now find the mass! Horray!

[@fleurtastic]

Hey there, I can't seem to find AS level "fluids" :/

[@DrPhysicsA]

Thanks. All good wishes for Thursday.

[@sierracanvill3147]

qe=qvB e=vB hence v=e/B.-(1) F=qvB and F=mv^2/r...so we get q/m=v/Br..-(2) from (1) and (2), q/m=e/B^2R...is this right? how do i bring it to the result u've got?

[@sierracanvill3147]

i'm not getting it.why have you derived an equation for r?what are we gonna do with it?i mean,i,have got the result q/m=e/B^2r,while you have got it as q/m=2v/B^2r^2 in your video....what i wanna know is that how the two results are different from one another

[@sierracanvill3147]

what makes the charged particle go in a circular motion in a magnetic field?

[@neilkrupa]

at around 11:00 you have an electron being attracted towards the anode and a mag field directed into the page. Why is the motion of the electron directed downwards when due to the LHR the current is moving right, mag field is into the page, shouldn't the motion of the electron be upwards?

[@sujanaunonymous2788]

is the electric field force(upwards) = gravitational force(downwards) and is electric field force = viscosity force.. because above it is said????????????

[@sumankhadkaanimeonly1935]

thank you so much for your video it helped me a lot :)

[@DrPhysicsA]

It doesn't. The electrons from the cathode hit the atoms of hydrogen in the tube and ionise them. The protons which remain will be attracted to the -ve plate.

[@sierracanvill3147]

why is there no viscous drag when electric field is applied?

[@alphie10]

i see but then if he discovered that the basic charge on the electron was -1.6 x 10^-19 and that the other charges were multiples of this number then wouldnt it make more sense to use the smallest possible multiple of -1.6 x 10^-19 as the basic number of charge on an electron so numbers like -0.8 x 10^-19 as its still a multiple of the actual charge

[@syedsafi6455]

but the formula of charge to mass ratio of electron in my text book is e/m=E/B^2r.

[@Izzatmashoori]

why does the proton come from the cathode?

[@Gazeta2nd]

If only I had seen this prior to my test today :P. I still understand it anyways, so I'm ok.

[@generalgrievous5483]

In which videos do you cover photoelectric effect

[@DrPhysicsA]

Try kzbin.info/www/bejne/mqiyZKyhmbJ3r9E at 4:03

[@hibarikyoya4051]

thanks sir..................... wonderful explanation

[@CrestinaBerzentho]

Hello, Today I want to Thank you For This video, this Exact Experiment, This Exact Explanation was applied to the Physics unit 4 Edexcel Paper and I think I Aced it. Thank you so Much. I think There Should Be a way to Donate to Your work. at least I would want to donate After I get a Job. please let me know if there is a way.

[@DrPhysicsA]

Kind of you to say so. Thanks.

[@Dyslexic-Artist-Theory-on-Time]

Thanks for sharing!!!

[@havishg5638]

how does he know velocity of oil drop

[@nahom4062]

thank you

[@sierracanvill3147]

yeah!! thnx!

[@ayonendubiswas6078]

why do we need to evacuate the jar

[@lukewarmbeverage6088]

So the electrons don't scatter by hitting air particles

[@aishilaha5311]

is that mathematical reason in cl xii standard...? i got the point......thank you sir.

[@AjayKumar-bm8tt]

AISHI LAHA hi

[@manfredgeilhaupt5070]

mass and charge of an electron from theory

[@simonb8988]

I wish I understood that math, but I don’t.

[@fleurtastic]

cheers ;D

[@praiseokwu1433]

Whose here 9 years later

[@dexz8721]

Can i marry your brain?