# 29.2 Discovery of the parts of the atom: electrons and nuclei  (Page 2/7)

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To see how the amount of deflection is used to calculate ${q}_{e}/{m}_{e}$ , note that the deflection is proportional to the electric force on the electron:

$F={q}_{e}E.$

But the vertical deflection is also related to the electron’s mass, since the electron’s acceleration is

$a=\frac{F}{{m}_{e}}\text{.}$

The value of $F$ is not known, since ${q}_{e}$ was not yet known. Substituting the expression for electric force into the expression for acceleration yields

$a=\frac{F}{{m}_{e}}=\frac{{q}_{e}E}{{m}_{e}}\text{.}$

Gathering terms, we have

$\frac{{q}_{e}}{{m}_{e}}=\frac{a}{E}\text{.}$

The deflection is analyzed to get $a$ , and $E$ is determined from the applied voltage and distance between the plates; thus, $\frac{{q}_{e}}{{m}_{e}}$ can be determined. With the velocity known, another measurement of $\frac{{q}_{e}}{{m}_{e}}$ can be obtained by bending the beam of electrons with the magnetic field. Since ${F}_{\text{mag}}={q}_{e}\text{vB}={m}_{e}a$ , we have ${q}_{e}/{m}_{e}=a/\text{vB}$ . Consistent results are obtained using magnetic deflection.

What is so important about ${q}_{e}/{m}_{e}$ , the ratio of the electron’s charge to its mass? The value obtained is

$\frac{{q}_{e}}{{m}_{e}}=-1\text{.}\text{76}×{\text{10}}^{\text{11}}\phantom{\rule{0.25em}{0ex}}\text{C/kg (electron).}$

This is a huge number, as Thomson realized, and it implies that the electron has a very small mass. It was known from electroplating that about ${\text{10}}^{8}\phantom{\rule{0.25em}{0ex}}\text{C/kg}$ is needed to plate a material, a factor of about 1000 less than the charge per kilogram of electrons. Thomson went on to do the same experiment for positively charged hydrogen ions (now known to be bare protons) and found a charge per kilogram about 1000 times smaller than that for the electron, implying that the proton is about 1000 times more massive than the electron. Today, we know more precisely that

$\frac{{q}_{p}}{{m}_{p}}=\text{9.58}×{\text{10}}^{7}\phantom{\rule{0.25em}{0ex}}\text{C/kg}\left(proton\right),$

where ${q}_{p}$ is the charge of the proton and ${m}_{p}$ is its mass. This ratio (to four significant figures) is 1836 times less charge per kilogram than for the electron. Since the charges of electrons and protons are equal in magnitude, this implies ${m}_{p}=\text{1836}{m}_{e}$ .

Thomson performed a variety of experiments using differing gases in discharge tubes and employing other methods, such as the photoelectric effect, for freeing electrons from atoms. He always found the same properties for the electron, proving it to be an independent particle. For his work, the important pieces of which he began to publish in 1897, Thomson was awarded the 1906 Nobel Prize in Physics. In retrospect, it is difficult to appreciate how astonishing it was to find that the atom has a substructure. Thomson himself said, “It was only when I was convinced that the experiment left no escape from it that I published my belief in the existence of bodies smaller than atoms.”

Thomson attempted to measure the charge of individual electrons, but his method could determine its charge only to the order of magnitude expected.

Since Faraday’s experiments with electroplating in the 1830s, it had been known that about 100,000 C per mole was needed to plate singly ionized ions. Dividing this by the number of ions per mole (that is, by Avogadro’s number), which was approximately known, the charge per ion was calculated to be about $1\text{.}6×{\text{10}}^{-\text{19}}\phantom{\rule{0.25em}{0ex}}\text{C}$ , close to the actual value.

are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
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