Mass spectometer and relativity

[evelyncanarvon]

Hi, I had a homework question in my physics class that I'm not totally sure about. We're supposed to design (not actually build, just explain on paper) a mass spectrometer that can measure the speed of electrons going at .998c, so taking into account special relativity. Here are my questions:

Would it basically be the same as a normal spectrometer, same design?

How would you account for relativity? I think you would assume that the mass would get bigger in your reference frame, so you would have to divide by that lorentz factor to get the object's rest mass. Is this right? What about length contraction? Do you just multiply r by the lorentz factor?

Also, how would you actually set up the magnetic field and the electric field?

Any help would be greatly appreciated. Thanks!

 

[azntoon]

Yes, it would be essentially the same design as a normal mass spectrometer. However, there are some special considerations that need to be taken into account for measuring particles moving at speeds close to the speed of light. To account for relativity, you would have to use the Lorentz factor to calculate the rest mass of the particle. The Lorentz factor is calculated by dividing the particle's total energy by its rest energy. You would also need to take length contraction into account, which means that you would have to multiply the particle's initial size (r) by the Lorentz factor to get the size in your reference frame. As for setting up the magnetic and electric fields, you would need to use the Lorentz force equation to determine the force on the particle. This equation takes into account the particle's charge (q), velocity (v), and the magnetic and electric fields. Thus, you would need to set up the electric field so that it is in the direction of the particle's velocity, and the magnetic field should be orthogonal to the electric field.

 

[R0man]

Hi there,

Designing a mass spectrometer that takes into account special relativity can be a challenging task, but it is definitely doable. To answer your first question, it would not be the same as a normal spectrometer. The design would have to take into account the effects of special relativity on the mass and velocity of the electrons being measured.

To account for relativity, you are correct in assuming that the mass would increase in your reference frame. This is known as the relativistic mass and it is given by the formula m = m0/√(1-(v/c)^2), where m0 is the rest mass, v is the velocity, and c is the speed of light. So, in your case, the rest mass of the electrons would be divided by the Lorentz factor, which is √(1-(.998c/c)^2) = √(1-0.998^2) = 0.0625. This means that the mass of the electrons would be about 16 times larger in your reference frame.

As for length contraction, it would indeed affect the design of the mass spectrometer. The distance between the electric and magnetic fields would appear shorter in your reference frame due to the electrons' high velocity. This means that the distance between the fields, r, would have to be multiplied by the Lorentz factor to account for length contraction.

To set up the magnetic field, you would need to use a strong magnet and adjust its strength to ensure that it can bend the path of the electrons at .998c. As for the electric field, it would have to be carefully calibrated to accelerate the electrons to that speed while also taking into account the relativistic mass.

Overall, designing a mass spectrometer that takes into account special relativity would require careful consideration and calculations. I hope this helps and good luck with your homework!