What is the velocity of a proton with an energy of 0.12 keV?

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SUMMARY

The velocity of a proton with an energy of 0.12 keV is calculated to be approximately 1.5 x 105 m/s. The conversion from electron volts (eV) to joules (J) is crucial, where 0.12 keV equals 120 eV, which translates to 1.92 x 10-17 J when multiplied by the charge of an electron (1.6 x 10-19 C). The formula used for calculating velocity is derived from kinetic energy, specifically v = sqrt(2E/m), where E is energy and m is mass. Dimensional analysis is recommended for accurate unit conversions.

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  • Understanding of kinetic energy equations in physics
  • Familiarity with electron volts (eV) and their conversion to joules (J)
  • Basic knowledge of dimensional analysis
  • Proton mass (1.7 x 10-27 kg)
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Homework Statement



Calculate the veolcity of a proton of energy 0.12 keV

proton mass = 1.7 x 10^-27

Homework Equations


The Attempt at a Solution



I thought...

0.12 keV = 120 eV

120/1.60 x 10^-19 = 7.5 x 10^20 J

E = 0.5mv^2

sqrt(2E/m) = v

but I'm getting something to x 10^23 so its obviously wrong.

its A-Level physics so shouldn't be a really complex answer...

Going wrong somewhere but can't work it out. Probably where I divided by the charge of an electron?

Any help appreciated.

James
 
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What exactly is an electronVolt?
 
You divided instead of multiplying. Try using dimensional analysis to convert from eV to Joules. It takes a lot of guess work out of the problem.
 
willem2 said:
What exactly is an electronVolt?

By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electrostatic potential difference of one volt. (from Wiki)

efekwulsemmay said:
You divided instead of multiplying. Try using dimensional analysis to convert from eV to Joules. It takes a lot of guess work out of the problem.

Oh, my tutor told me to divide...

Is it because 1 Volt = 1 Joule/1 Coulomb

There for Joules = V * C ?

So eV multiplied but the charge of an electron give the Energy of the proton?

Also, I've not heard of Dinentional Analysis before, what exactly is it?

Thanks a lot

james
 
So would the correct answer be...

120 * 1.6 x 10-19

= 1.92 x 10 -17

sqrt(2*1.92 x 10 -17/1.7 x 10-27) = v = 1.5 x 105 ms-1
 

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