Question

4.) A positively charged methane ion CH+ 4 (molar mass 16.1g/mol) is deflected in mass spectrometer with magnetic field B = 3.2T. The ion is collected at the distance D = 1.7cm along the screen.
a) Find the speed of the CH+ 4 -ion in the region with magnetic field!
b) The methane-ion is accelerated through a voltage V applied between ion source and the plate. Find the voltage V ! Is the source at the higher of lower potential relative to the plate?

Answer 1

The radius/distance (D) produced by magnetic field B is given by,

(m= mass, v = velocity, q = 1.6 x 10-19 C)

Here given, D = 1.7 cm = 1.7 x 10-2m, m = 16.1g/mol = 16.1 x 10-3 Kg/mol, B = 3.2 T.

(a). Now,

  

= 1.7 x 10-2 x 1.6 x 10-19  x 3.2 / 16.1 x 10-3

= 5.406 x 10-19 m/s.

(b). Now, the velocity and potential is given by,

where V = accelerating voltage.

  

= 16.1 x 10-3 x 5.406 x 10-19 x 5.406 x 10-19 / 2 x 1.6 x 10-19

= 147.03 x 10-22

=1.47 x 10-20 volt.