Question

After the velocity selector, a mass spectrometer allows the charged particle to enter a region of magnetic field only, where it follows a curved trajectory and hits a detector which records his position. Your mass spectrometer has the velocity selector set for 2.39 x 10^5 m/s and a magnetic field of 0.1 Tesla. You record particles on the detector 20 cm from the entrance slit. What type of particle have you detected?

1)electron
2)hydrogen ion H+
3)positron
4)helium ion He+

Answer 1

L=0.2 m => R=0.1 m
mv²/R=qvB
q/m= v/RB = 2.39•10⁵/0.1•0.1 =2.39•10⁷ C/kg

helium ion He+
q/m= 1.6•10⁻¹⁹/(4•1.67•10⁻²⁷+9.1•10⁻³¹) =2.39•10⁷ C/kg