I have to explain electron-volts as part of an antimatter essay (when describing the amounts of energy accelerators can imbue in a particle), but no explaination I’ve found has helped me understand… I don’t want to use some definition I don’t know, so could someone put it into lay-terms so I might have a better idea of what they are?
It’s a unit of energy. An electric charge at rest in an electric potential of 1 volt has a potential energy of 1 electron-volt. The charge on one electron is 1.6 x 10[sup]-19[/sup] Coulombs, making an electron-volt 1.6 x 10[sup]-19[/sup] Joules.
An electron-volt is a unit of energy. A volt is measure of electric potential, V=U/q. An electron has a specific charge. So, if you multiply the charge of an electron, 1.602e-19 C (coulombs) by 1 V, you get an electron volt, which is 1.602e-19 joules. It’s just a way to record an amount of energy. You can put any sort of multiplier before an eV, so you can get kilo-electron volts, mega-electron volts, giga-electron volts, and so on.
Honestly, I would suggest going and borrowing a college intro. physics textbook and look at the chapters on electricity and magnetism. With any luck, they can explain better than I can.
Yeah, the newest accelerators are up to 200 GeV, I think.
Okay, start again. My physics class hasn’t dealt with any sort of electricity, and that’s one area where I’m very, very weak.
So, what’s electric potential? :o
Others may chime in here, but here’s a stab at a simple explanation, suitable for understanding the units at least.
Think of electric potential as a potential to do work, the same way as you might think of potential gravitational energy (i.e. some object at a particular height on earth has potential energy mgh ). It’s important to realize that it’s a relative measurement; the potential is measured from A to B. For example, if all we care about is the height from the court, a basketball 10 ft. off the ground at sea level has roughly the same grav. PE as one 10 ft. off the ground on a court 100 ft above sea level.
To extend the analogy, think of ‘charge’ as the mass of an object. The potential (gravity-height) is going to work on a 0.5-kg. ball the same as on a 1000-kg car, but you’d rather be hit by a falling ball than a falling car – that is, the car has more energy at the same height in the same field.
To understand the units, if ‘charge’ ~ ‘mass’ then ‘volts’ ~ ‘g-meters’ . You could measure energy in kilogram-g-meters. ( 1 kg-g-m = 9.8 Joules )
At 10 ft. (= 3 m) the ball has 1.5 kg-g-m’s and the car has 3000 kg-g-m’s .
Slight amendment : You should think of electric potential as a potential to do work because it is potential to do work. Electric fields are conservative, too, just the way a gravitational field is.
No, the potential to do work is called Potential Energy (PE.)
Electric Potential is it’s own thing. Analogy: it’s like the
height above the Earth’s surface. If you lift a boulder up
to a certain height, then you store some PE. But what if
there’s no boulder, but only a height exists? The gravity
field is still there. So is the stuff called “A Potential.”
Potential is fairly hard to explain. Here are several
attempts:
http://amasci.com/miscon/volts.html
If you know about magnetic fields and flux lines or “lines
of force”, you can think of Potential as being like a stack
of layers in the magnetic field which are perpendicular
to the field lines. Magnetic fields are MADE of “Potential,”
and this is true of gravity fields and Electric Fields too.
We can visualize a field as being like a bunch of fibers,
or we can visualize fields as being like a pile of thin
layers, and these layers are made of Potential.
Where electric fields are involved, Potential is measured
in terms of Volts.
Think of Electrical Potential as being like “Electrical Height,”
with Volts being roughly equivalent to meters above the
Earth. If we lift an electric charge up through a certain number
of Volts, then we store some potential energy. If we let the
blob of charge fall back down again, the stored energy is
converted into Kinetic Energy again.
Letting a rock fall through a certain height gives it a
certain amount of kinetic energy. Letting an electron
fall through a certain Voltage gives it a certain amount of
kinetic energy.
The forumula for charge, volts, and energy is:
U = V * Q (U is energy in Joules, Q is charge in Coulombs.)
So, if we’re dealing with elementary charges, then coulombs
are way too big. The quantity of charge carried by an electron
would be a more convenient unit. So, the above equation
can be changed: Q remains a quantity of charge, but it’s
expressed in numbers of electron-charges. U then becomes
volts times number of elementary charges, or volts times
electrons, or electron-volts.
Look, it’s not that complex. Take a pair of parallel metal plates (electrodes), and hook them up to a 1-volt battery. You take one electron and put it gently on the negative electrode. The electro will get repelled by the negative electrode and attracted to the positive electrode. Since the potential difference between the two is 1 volt, the electron will hit the positive electrode with a kinetic energy of 1 electron-volt.
X-ray generators work exactly like that. A heated filament acts as a source of free electrons, and a nearby piece of metal (usually tungsten) acts as a target. You take a 60,000 volt power supply and hook up the positive output to the tungsten target and the negative output to the filament. When you turn it on, the free electrons get accelerated by the electric field and collides with the target with a kinetic energy of 60,000 electron-volts (or 60 keV) each. Each collision can cause an emission of an X-ray photon up to 60 keV in energy.