Hi, i'm having a bit of trouble with a question here, if anyone can give me some pointers, it'd be really helpful.
Inside a small electron gun, an electron is passed through a potential difference of 100kV. Initially at rest, the electron emerges from the electron gun with a speed comparable to the speed of light.
Use the Newtonian expression for kinetic energy to estimate the electron's final speed.
OK, i know that the newtonian expression for kinetic energy is Ek=1/2 mv^2, but surely the final speed of the electron is the speed of light, or am i missing something here ?
I can work out the kinetic energy of the electron easy enough, but i thought i already had the speed, so what's going on here ?
Any help would be appreciated thanks.
2007-07-12 05:20:27 · 3 answers · asked by David M 1 in Science & Mathematics ➔ Physics
They are asking you to ignore relativity and just use good old Newtonian definitions of energy.
KE = 1/2mv^2 = e*V (where V is potential difference, not 1 volt)
v = sqrt (2KE / m) = sqrt (2eV/m)
Look up the fundamental charge (e) and mass of an electron (m). plugnchug. If your answer is small compared to c, you are cool. If it is a significant fraction of c (or bigger than c), you really need to be using relativistic formulae (so that is probably the point of what they want you to see in this problem).
2007-07-12 05:27:18 · answer #1 · answered by Anonymous · 1⤊ 0⤋
It's a poorly worded question, but I'm guessing that the idea is this: The _real_ speed is (close to) the speed of light; but the speed predicted by Newtonian mechanics would be quite different from that. If I were writing the question I would have said, "If the electron were obeying Newtonian mechanics, what would its predicted speed be, according to the Newtonian expression for kinetic energy?"
2007-07-12 05:32:42 · answer #2 · answered by RickB 7 · 0⤊ 0⤋
a million. No merchandise can holiday at mild velocity. 2. Newtonian mechanics (NM) and specific relativity (SR) are the two valid for small and massive hundreds. 3. NM and SR are the two valid for gadgets at consistent velocity. 4. NM and SR are the two valid for gadgets with small kinetic power. 5. NM isn't valid while the kinetic power is extremely great.
2016-12-14 06:43:09 · answer #3 · answered by ? 4 · 0⤊ 0⤋