Energy                How Big is an Electron Volt? An electron 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 A 50,000 BTU Furnace heating your home for one hour 360,000 joules 4.5 million joules 52 million joules 2.2 x 1024 electron volts WOW! thats 2.2 Trillion TeV or 2.2 Trillion Trillion electron volts Even Bigger 28  x 1024 electron volts And still more 324 x 1024 electron volts  Sample question 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 the loop.    Question 1 The 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 this point?  Teacher's Note Don't confuse mass and weight  The Solution Kinetic energy = 1/2 m v2 = 1/2 x 200kg [15m/s]2 = [1/2 x 200 x 225]J = 22 500 J  Question 2 The loop is 10 m high. How much potential energy will the car have gained when it reaches the top of the loop?  Teacher's Note Don't confuse mass and weight  The Solution Change in g.p.e. = mgh = 200kg x 10m/s2 x 10m = 20 000 J  Question 3 How much kinetic energy will the car have at this point?  The Solution 20 000 J of k.e. has changed to g.p.e., so new k.e. = (22 500 - 20 000) J = 2,500 J  Question 4 For 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.  The Solution k.e. of car at 3m/s = 1/2 x 200kg x [3m/s]2 = (1/2 x 200 x 9) J = 900 J which is less energy than the car actually has, so it must be going faster than this.  Examiner's Note This has been answered the 'easy' way, which is good. You could have changed the subject of the K.E. formula to get this: k.e = 1/2 x m x v2 v2 = k.e x 2/m v2= 2,500 X 2/200 = 50/2 =25 Therefore v = 5m/s (squareroot of 25) But it's easy to make a mistake doing it this way. So be careful. Why is it impossible, at this point in time, to convert energy into matter?  The Answer It 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 particles. It's 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. Koji Mukai, with David Palmer, Andy Ptak and Paul Butterworth for the Ask a High-Energy Astronomer .