Question

In Milikan’s oil drop experiment, an oil drop carrying charge Q is held stationary by a potential difference f 2400V between plates. To keep the drop of half the radius stationary, the potential difference has to be made 600V. what is the charge on the second drop?

Answer 1

quite confused?? could you please model

Answer 2

Which part of the question is not clear?

Answer 3

are we having two drops??

Answer 4

Yeah first a drop is taken and the results are noted.Then another drop with half the radius is taken

Answer 5

E/r = F/qr => V = F/qr ,,, where r is the distance

Answer 6

But that is distance from the charge

Answer 7

yeah ... somehow it seems that at certain point ... no matter how much the charge ... it will remain static.

Answer 8

Yeah now have to see how the radius of the drop affects the situation

Answer 9

at certain distance

Answer 10

i don't think radius will affect the distance ... because usually you need microscope to see the oil drop ... basically, it's the mass of the drop what will affect ...

Answer 11

yeah i know that ... i studied it in my 11 or 12 grade ... but i forgot

Answer 12

That aside I also have another question.Please see if you can get it
"There are 27 drops of a conducting fluid.Each has a radius r and they are charged to a potential V.All these drops combine to form a bigger drop.What is it's potential?

Answer 13

first let's nail this millikan oil drop experiment ...

Answer 14

Ok

Answer 15

oops .. sorry, that was supposed to + ...and negative -- plate on top

Answer 16

But he said it is stationary.What is keeping it stationary?

Answer 17

forced will be balanced at certain point ... that makes it stationary

Answer 18

I mean what here is counteracting the electric field to make it stop moving

Answer 19

gravitational force

Answer 20

But the m here is not given.Damn I got stuck here on lots of questions because I didnt think this is on earth and gravitational force is acting

Answer 21

lol ... i had the same problem. i never understood milikan oil drop experiment

Answer 22

So can we take m/V is constant and measure mass?

Answer 23

most likely the mass in calculated form density and volume/

Answer 24

Yeah so that settles it I think.Now it's just equating those two

Answer 25

still one parameter is missing

Answer 26

What is it?

Answer 27

distance .. or height

Answer 28

Cant we just take distance d for both?

Answer 29

I mean it's just a constant right?

Answer 30

yeah ...i was thinking the same/

Answer 31

So thanx for that.Please see the other question too

Answer 32

sure ... will you do the calculation?

Answer 33

Yeah ill do the calculations

Answer 34

There are 27 drops of a conducting fluid.Each has a radius r and they are charged to a potential V.All these drops combine to form a bigger drop.What is it's potential?

Answer 35

having same diameter?

Answer 36

Yep equivalent drops

Answer 37

and ... and what do we call that ...capability of holding charge??

Answer 38

What?Didnt get you

Answer 39

i am not quite sure myself ... i never understood electricity and magnetism.

Answer 40

Yeah I am presently doing Electromagnetism

Answer 41

i was planning to do too ... since i had pretty close exams. but let's focus on the question first.

Answer 42

Yeah so by equating the volumes i got the radius for the fianl sphere as 3r

Answer 43

charge will be 27 times ... but there's something fishy

Answer 44

Firstly what is causing the potentail there is not given

Answer 45

how can we define potential??

Answer 46

work done on certain distance.

Answer 47

It's potential energy per unit charge in the electric field

Answer 48

So maybe we can assume all this is going on in a uniform electric field