Energy of a proton around a magnetic field

[kitkat2950]

A proton moves in a circular path perpendicular to a 4.30 T. magnetic field. The radius of its path is 7.5 cm. Calculate the energy of the proton in electron-volts.


I'm not sure which equation to use. I tried using m=rqB/v and found the velocity. However, I'm not sure how to relate that to energy. Mass of proton equals 1.67E-27. Q of proton = 1.6E-19. 1eV=1.6E-19 J.

 

[Hootenanny]

Welcome to PF,

A proton moves in a circular path perpendicular to a 4.30 T. magnetic field. The radius of its path is 7.5 cm. Calculate the energy of the proton in electron-volts.

I'm not sure which equation to use. I tried using m=rqB/v and found the velocity. However, I'm not sure how to relate that to energy. Mass of proton equals 1.67E-27. Q of proton = 1.6E-19. 1eV=1.6E-19 J.

What type of energy would you say the proton possesses?

 

[kitkat2950]

Thank you, I love House by the way. I would say it has kinetic energy. SO would I use KE=1/2mv^2? But then I always get confused on what work equals, because I think I need to find work to solve the equation. I think W=KE+PE, and I don't think there is any Pe. Would the work just equal the kinetic energy? Nothing I submit seems to be right.

 

[Hootenanny]

Thank you, I love House by the way.

I can't wait for the next season

I would say it has kinetic energy. SO would I use KE=1/2mv^2?

Correct! Assuming of course that the proton is non-relativistic.

But then I always get confused on what work equals, because I think I need to find work to solve the equation. I think W=KE+PE, and I don't think there is any Pe. Would the work just equal the kinetic energy? Nothing I submit seems to be right.

Correct again, there is no potential energy and hence the total energy of the proton is simply it's kinetic energy.

 

[kitkat2950]

So velocity is v=.075m X 1.6X10^-19C X 4.30T / 1.67X10^-27. Which equals 3.09X10^7. I then used KE=.5 X 1.6X10^-19 X (3.09X10^7)^2 and came up with 7.637X10^-5J. I multiplied that by 1eV/1.6X10^-19J and got 4.77X10^14. But it was still wrong. Any other suggestions?

 

[Hootenanny]

So velocity is v=.075m X 1.6X10^-19C X 4.30T / 1.67X10^-27. Which equals 3.09X10^7. I then used KE=.5 X 1.6X10^-19 X (3.09X10^7)^2 and came up with 7.637X10^-5J. I multiplied that by 1eV/1.6X10^-19J and got 4.77X10^14. But it was still wrong. Any other suggestions?

Why have you multiplied by the charge here, instead of the mass? The blue section is also incorrect and is unnecessary if you simply use the mass.

 

[kitkat2950]

Oh thank you. I knew it had to be something stupid. It was right!

 

[Hootenanny]

Oh thank you. I knew it had to be something stupid. It was right!

A pleasure.