How Big is an Electron Volt?
volt is a measure of energy. An electron volt is
the kinetic energy gained by an electron passing
through a potential difference of one volt.
This unit can be confusing. A volt is
not a measure of energy.
An electron volt is a measure of energy.
An electron volt is very tiny.
103 eV = 1 KeV
106 eV = 1 MeV
109 eV = 1 GeV
1012 eV = 1 TeV
one eV = 1.602 x 10-19 joules
Examples of more familiar measures of energy:
BTU-h, joule, erg, kw-hour
100 watt light bulb burning for one hour
Kinetic Energy of a 1900 lb INDY 500 car (with
driver and fuel) traveling at 230 mph
50,000 BTU Furnace heating your home for one
4.5 million joules
52 million joules
2.2 x 1024 electron volts WOW!
thats 2.2 Trillion TeV or 2.2 Trillion Trillion
28 x 1024 electron volts
And still more
324 x 1024 electron volts
Diane is an engineer designing a theme park ride. A
car will be 'fired' along the level part of a track by
a big catapult, so it is moving quickly when it hits
the loop. The car must have enough energy to complete
car has a mass of 200kg. Diane plans for the car to be
moving at 15 m/s by the time it reaches the base of
the loop. How much kinetic energy will the car have at
Don't confuse mass and weight
Kinetic energy = 1/2 m v2
= 1/2 x 200kg [15m/s]2
= [1/2 x 200 x 225]J
22 500 J
loop is 10 m high. How much potential energy will the
car have gained when it reaches the top of the loop?
Don't confuse mass and weight
Change in g.p.e. = mgh
= 200kg x 10m/s2 x 10m
20 000 J
much kinetic energy will the car have at this point?
20 000 J of k.e. has changed to g.p.e., so new k.e.
= (22 500 - 20 000) J
safety reasons, Diane does not want the car to travel
at less than 3 m/s at any point in the loop. Would
this car fulfil this requirement? Show your working.
k.e. of car at 3m/s
= 1/2 x 200kg x [3m/s]2
= (1/2 x 200 x 9) J
which is less energy than the car actually has, so it
must be going faster than this.
This has been answered the 'easy' way, which is good.
You could have changed the
subject of the K.E. formula to get this:
= 1/2 x m x v2
= k.e x 2/m
2,500 X 2/200
= 50/2 =25
Therefore v = 5m/s (squareroot of 25)
it's easy to make a mistake doing it this way. So be
is it impossible, at this point in time, to convert
energy into matter?
happens all the time. Particle accelerators convert
energy into subatomic particles, for example by
colliding electrons and positrons. Some of the kinetic
energy in the collision goes into creating new
not possible, however, to collect these newly created
particles and assemble them into atoms, molecules and
bigger (less microscopic) structures that we associate
with 'matter' in our daily life. This is partly
because in a technical sense, you cannot just create
matter out of energy: there are various 'conservation
laws' of electric charges, the number of leptons
(electron-like particles) etc., which means that you
can only create matter / anti-matter pairs out of
energy. Anti-matter, however, has the unfortunate
tendency to combine with matter and turn itself back
into energy. Even though physicists have managed to
safely trap a small amount of anti-matter using
magnetic fields, this is not easy to do.
Also, Einstein's equation, Energy = Mass x the square
of the velocity of light, tells you that it takes a
huge amount of energy to create matter in this way.
The big accelerator at Fermilab can be a significant
drain on the electricity grid in and around the city
of Chicago, and it has produced very little matter.
Mukai, with David Palmer, Andy Ptak and Paul
for the Ask a High-Energy Astronomer .