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A black and white image of scientist J. J. Thomson wearing a coat and oval shaped spectacles.
J. J. Thomson (credit: www.firstworldwar.com, via Wikimedia Commons)
A diagram of the glass apparatus that was used to discover the electron in J. J. Thompson’s experiment.
Diagram of Thomson’s CRT. (credit: Kurzon, Wikimedia Commons)
Image of a cathode ray tube on x axis between two inverted L shaped north and south pole magnets on y axis, with z axis as a wire carrying high voltage supply to the charging plates inside the C R T. Zoomed image of the charging plate area inside the C R T showing the intersection of magnetic field between the poles in red lines towards south pole on the y axis along with an electron beam in green color line with velocity v toward right on the x axis.
This schematic shows the electron beam in a CRT passing through crossed electric and magnetic fields and causing phosphor to glow when striking the end of the tube.

To see how the amount of deflection is used to calculate q e / m e size 12{q rSub { size 8{e} } /m rSub { size 8{e} } } {} , note that the deflection is proportional to the electric force on the electron:

F = q e E . size 12{F=q rSub { size 8{e} } E} {}

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

a = F m e . size 12{a= { {F} over {m rSub { size 8{e} } } } } {}

The value of F size 12{F} {} is not known, since q e size 12{q rSub { size 8{e} } } {} was not yet known. Substituting the expression for electric force into the expression for acceleration yields

a = F m e = q e E m e . size 12{a= { {F} over {m rSub { size 8{e} } } } = { {q rSub { size 8{e} } E} over {m rSub { size 8{e} } } } "." } {}

Gathering terms, we have

q e m e = a E . size 12{ { {q rSub { size 8{e} } } over {m rSub { size 8{e} } } } = { {a} over {E} } } {}

The deflection is analyzed to get a size 12{a} {} , and E size 12{E} {} is determined from the applied voltage and distance between the plates; thus, q e m e size 12{ { {q rSub { size 8{e} } } over {m rSub { size 8{e} } } } } {} can be determined. With the velocity known, another measurement of q e m e size 12{ { {q rSub { size 8{e} } } over {m rSub { size 8{e} } } } } {} can be obtained by bending the beam of electrons with the magnetic field. Since F mag = q e vB = m e a size 12{F rSub { size 8{"mag"} } =q rSub { size 8{e} } ital "vB"=m rSub { size 8{e} } a} {} , we have q e / m e = a / vB size 12{q rSub { size 8{e} } /m rSub { size 8{e} } =a/ ital "vB"} {} . Consistent results are obtained using magnetic deflection.

What is so important about q e / m e size 12{q rSub { size 8{e} } /m rSub { size 8{e} } } {} , the ratio of the electron’s charge to its mass? The value obtained is

q e m e = 1 . 76 × 10 11 C/kg (electron). size 12{ { {q rSub { size 8{e} } } over {m rSub { size 8{e} } } } = - 1 "." "76" times "10" rSup { size 8{"11"} } " C/kg"} {}

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 10 8 C/kg size 12{"10" rSup { size 8{8} } " 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

q p m p = 9.58 × 10 7 C/kg (proton), size 12{ { {q rSub { size 8{p} } } over {m rSub { size 8{p} } } } =9 "." "57" times "10" rSup { size 8{7} } " C/kg"} {}

where q p size 12{q rSub { size 8{p} } } {} is the charge of the proton and m p size 12{m rSub { size 8{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 = 1836 m e size 12{m rSub { size 8{p} } ="1836"m rSub { size 8{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 . 6 × 10 19 C size 12{1 "." 6 times "10" rSup { size 8{ - "19"} } " C"} {} , close to the actual value.

Questions & Answers

are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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Source:  OpenStax, College physics -- hlca 1104. OpenStax CNX. May 18, 2013 Download for free at http://legacy.cnx.org/content/col11525/1.1
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