Electricity and revolutions per second

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Homework Help Overview

The discussion revolves around a problem in classical physics concerning the motion of an electron in a hydrogen atom, specifically calculating the number of revolutions per second the electron makes while orbiting a proton.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to apply equations of motion and electrostatics to find the angular speed and subsequently the frequency of revolutions. Some participants suggest working algebraically before substituting numerical values. Others question the implications of the results in the context of classical physics at the atomic scale.

Discussion Status

Participants are exploring different approaches to the problem, with some providing guidance on rearranging equations and others pointing out potential errors in calculations. There is no explicit consensus on the correct method, but the discussion is productive with various interpretations being examined.

Contextual Notes

There is mention of the challenges posed by classical physics when applied to atomic-scale phenomena, indicating a potential limitation in the assumptions made in the problem setup.

abeltyukov
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Hi,

Homework Statement



In a simple model of the hydrogen atom, the electron moves in a circular orbit of radius 0.053 nm around a stationary proton. How many revolutions per second does the electron make?


Homework Equations



F = (kq1q2)/r^2 = (mv^2)/r

v = wr

The Attempt at a Solution



Charge of electron = -1.602 x 10^-19 C
Charge of proton = 1.602 x 10^-19 C
Mass of electron = 9.109 x 10^-31 kg

[(8.999 x 10^9)(1.602 x 10^-19)(1.602 x 10^-19)] / (0.053 x 10^-9) = (mv^2)/r

v = 0.002187 m/s

v = wr

0.002187 = w(0.053 x 10^-9)

w = 41267720.67


Any ideas on what I am doing wrong? Thanks!
 
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You may find it easier to work algebraically until the last moment and then plug the numbers in. With the equations you have you want to rearrange of the angular speed (omega). Once you find omega you will then need to find the frequency. Do you know the equation to find the frequency?
 
Can you give me an example please? Thanks!
 
abeltyukov said:
Can you give me an example please? Thanks!

I'm not sure that would be constructive. The answer you get may look a little weird but that is because this is an exercise in showing how classical physics breaks down at the nano scale.
 
You forgot to square the radius below the charges. This changes the velocity to 2187190m/s. Then, in order to find rev/s you just divide the velocity by 2*pi*r giving a final answer of 6.568*10^15 rev/s.
 

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