Weight of Electrons

[Nave]

First off I wasnt sure where to put this so i just put here. I was wondering if anybody knew of a lab or the equations to figure out weight of electrons. I know you have to do stuff with magnets and a cathode ray gun which i have access too..but what are the equations to figgure out the weight of electrons. I mean i all ready know how much they way i just wana like prove it to myself cuz i dont have anything better to do. I looked on the internet but i really havent found anything yet so any help will be appreciated.

[swansont]

First off I wasnt sure where to put this so i just put here. I was wondering if anybody knew of a lab or the equations to figure out weight of electrons. I know you have to do stuff with magnets and a cathode ray gun which i have access too..but what are the equations to figgure out the weight of electrons. I mean i all ready know how much they way i just wana like prove it to myself cuz i dont have anything better to do. I looked on the internet but i really havent found anything yet so any help will be appreciated.

 

You probably want the mass, rather than the weight.

 

You can do a Millikan oil drop experiment and use qE=mg

 

Or do an electron beam deflection and use m = er²B²/2V (derived in the link)

[5614]

the mass of an electron is 1/1836

 

i cant rememer the unit that this is... which really isnt good! sub-atomic particles have their own measuring system where a proton is 1 and neutron is 1 and an electron is 1/1836... i'll find out the name in a sec.

 

the weight of it depends on gravity and mass... you know it's mass already, weight is dependant on where the atom is and how much gravity there is there.

[Martin]

First off I wasnt sure where to put this so i just put here. I was wondering if anybody knew of a lab or the equations to figure out weight of electrons. I know you have to do stuff with magnets and a cathode ray gun which i have access too..but what are the equations to figgure out the weight of electrons. I mean i all ready know how much they way i just wana like prove it to myself cuz i dont have anything better to do. I looked on the internet but i really havent found anything yet so any help will be appreciated.

 

this is partly a science history question

JJ Thomson around (i think) 1895

did this experiment with a cathode ray tube where he measured the

CHARGE TO MASS ratio

by bending a beam of electrons using both plates (electrostatic) and coils (magnetic) forces

 

later R. Millikan was able to measure the charge of electrons by having tiny oil droplets of a known weight and charging them and watching the cloud of charged droplets drift, in an electric field between two plates.

 

so the two pieces of info were combined to give us the MASS itself.

 

 

If you want to do the stuff with the cathode ray tube then focus on the

CHARGE TO MASS ratio. it is a real important number

and that is what JJThomson experiment determined

and it is popularly called his "discovery of the electron"

 

he discovered that there was a particle, that the cathode ray consists of a stream of these particles, that the particle has a definite mass and a definite charge------and he couldnt determine what either of them was but at least he could figure out their ratio.

 

that 1895 experiment was the beginning of modern physics

Planck black body radiation curve came later: 1900

Einstein photoelectric effect and special rel came later: 1905

 

Look for JJ Thomson on google, must be lots

[ecoli]

electron mass = 9.10938188 × 10^-31 kilograms

[Martin]

the mass of an electron is 1/1836

 

i cant rememer the unit that this is... which really isnt good! sub-atomic particles have their own measuring system where a proton is 1 and neutron is 1 and an electron is 1/1836... i'll find out the name in a sec.

 

the weight of it depends on gravity and mass... you know it's mass already' date=' weight is dependant on where the atom is and how much gravity there is there.[/quote']

 

1/1836 is a good way to think of it IMO

the NIST fundamental constants site lists the

mass ratio of the proton to the electron as 1836.152... unless it has changed since i last looked.

 

he needs to think of an experiment to get a handle on the mass

 

if he could send electrons AT KNOWN SPEED between two plates,

so they were subjected to a sideways force, by the static electric field between the plates

and if he could then measure the deflection of the beam

that way he would have an F=ma thing.

he would know the sideways force that the electron is subjected to

and he would know the sideways drift speed that results (by measuring the deflection and knowing the speed of particles in the beam)

and so he would find out mass from F = ma.

 

but to do that he must know the charge on the electron because that

is what determines the force that an electric field applies to the particle!

let us assume he knows the charge (which JJThomson didnt)

then finding the mass is not going to be too difficult

 

good idea for a project!

[Nave]

5614 its 1/1837 of a Hydrogen atom

[Martin]

5614 its 1/1837 of a Hydrogen atom

 

 

that makes real good sense if it is 1/1836 of a proton!

 

 

because then, in electron masses, the proton weighs 1836

and the electron weighs 1

so the total of the two weighs 1836 +1 = 1837

[Martin]

 

...I know you have to do stuff with magnets and a cathode ray gun which i have access too..but what are the equations to figgure out the weight of electrons. I mean i all ready know how much they way i just wana like prove it to myself ...

 

 

can you get the specs for an electrostatic CRT

(like an oscilloscope or something)?

 

If you just want to convince yourself then if you have the specs someone here can help figure out.

 

the specs will show the beam going between two plates and getting deflected

 

if we know what voltage between the plates produces what angle of deflection then we are nearly there (that almost will tell the mass of the electron, but a little more info is needed like the speed of electrons in the beam and the separation between the plates)

 

the fact that the CRT works as the specs say it works is proof that the electron has a certain mass (because of F=ma, and it takes a certain force to give it a sideways shove, depending on its inertia, and the force is easy to calculate from the plate voltage)

[Nave]

well its a real cathode ray gun. you see in the old tvs they had a sort of somthing with them so if u mod a tv a bit you can have one...so i guess i could figure out the specs somehow :/

[Martin]

well its a real cathode ray gun. you see in the old tvs they had a sort of somthing with them so if u mod a tv a bit you can have one...so i guess i could figure out the specs somehow :/

 

if you dont have detailed published specs that gives good information

like the plate dimensions and plate voltage related to deflection etc

then I wouldnt know how to use it.

 

maybe Swantsont or Severian or some of the others can suggest

 

you may have to get someone else advice

 

all I know---to get the mass---is you have to give the little sucker a known amount of push and then be able to measure the resulting speed, the smaller the speed turns out to be, the bigger the mass was.

 

mass is inertia, it is resistance to being accelerated, basically you measure it with F = ma

(but the underlying eqn may be disguised

 

the way you give an electron a push is with voltage

 

so you have to have a real good handle on the voltage between the plates that creates the force that is pushing the electron (sideways say)

 

the more difficult the beam is to deflect (other things being equal, like the speed of the beam) the more massive must have been the particles

 

 

Maybe you should not use your old CRT with no specs. Maybe you should go somewhere they have a engineer-grade oscilloscope with circuit diagrams and a book of printed specs and read up on the oscilloscope specs

 

oscilloscopes work by deflecting a beam of electrons so the whole device totally depends on what the electron mass is. if you learn the basic operation of one you will be convinced that you know the mass of the electron

[ed84c]

well its a real cathode ray gun. you see in the old tvs they had a sort of somthing with them so if u mod a tv a bit you can have one...so i guess i could figure out the specs somehow :/

 

All tvs that arnt very new, thankyou

[JaKiri]

5614 its 1/1837 of a Hydrogen atom

 

The standard unit is, in fact, 1/12th the mass of an atom of Carbon 12, not a hydrogen atom.

[5614]

The standard unit is, in fact, 1/12th the mass of an atom of Carbon 12, not a hydrogen atom.

 

one sec, this has all confused me a bit... JaKiri, 1/12th the mass of C12 atom is the amu (atomic mass unit) of a proton or neutron and the 1/1836 is the amu of an electron?

if so then where does the 1/1837 that nave mentioned come from?

[swansont]

The standard unit is, in fact, 1/12th the mass of an atom of Carbon 12, not a hydrogen atom.

 

That's the atomic mass unit you are defining, not the electron mass. There are Avogadro's number of amu's in a gram.

[JaKiri]

Sorry, the point I was trying to make was that the mass is standardised from Carbon 12, not from Hydrogen.

 

The 1837 comes from 1386 + 1, because a hydrogen atom contains a proton and an electron, their combined masses being 1387 times the mass of an electron, and therefore the mass of an electron is that amountth (if you will) of the mass of a hydrogen atom.