17/01/2011
Protons and other things I’m working with in physics
Today is one of those red-letter days because it marks a turning point in my grasp on physics and the material we are working with. Last quarter was grueling, and my understand of the material was hard-earned and not as stable as I would have liked. But sliding into this quarter and a huge volume of new material, its astonishing how much translates from classical mechanics into electricity. We haven’t hit magnetism or optics yet, which I’m both excited and nervous about, but so far I’m happy that this quarter is fitting together so well conceptually. I’ll share my epiphany below, if you don’t care about math/physics you can stop reading here, even though you’ll be missing the best part.
I was asked to find the speed of a proton after it passed through an electric field with a potential energy difference of 190Volts.
So dredging up constants & formula I listed out these things that we hold as true.
Mass of a proton: mp = 1.673×10-27kg
Charge of proton: qp = 1.60×1019C
Law of Conservation of Energy
Classical Mechanics: mgh=(1/2)mv2
Electricity: potential energy difference: qV (this is the equivalent to mgh above)
Here’s where the insight happened, and for anyone who has spent time with physics this is probably on par with a toddler figuring out how to open a door, so its good for where I am.
I substituted potential mechanical energy with potential electrical energy, which works because the force of static charge is many powers greater than the force of gravity, but you can still find velocity from kinetic energy. For our purposes V=volts and v=velocity, an unfortunate reality of notation here.
qV = (1/2)mv2 -> v=(2qV/m)(1/2)
Solving for v we find that v=1.9×105m/s
And now you know. Victory.
