A mass spectrometer is an analytical device that measures the mass of ions (char

Question

A mass spectrometer is an analytical device that measures the mass of ions (charged atoms or molecules) with a special arrangement of electric and magnetic fields (see figure). In the velocity selector the magnitude of the electric field is E= 2000 V/m and the magnitude of the magnetic field is Bin = 0.028 T. The magnitude of the magnetic field in the deflection chamber with the detector array is B0,in = 0.042 T. The detector array records ion hits at position P = 46.3 cm from the entrance of the deflection chamber

a) How large is the radius of the path of those ions ? (look into the figure)

Explanation / Answer

for velocity selector ;

qvB = qE ;

v = E /B = 2000 / 0.028 = 71428.57 m /s ;

( a ) radius = 46.3 / 2 = 23.15 cm ;

( b )

mv^2 / r = qvB ;

mv / r = qB ;

m * 71429.57 / 0.2315 = ( 1.6 e -19 ) ( 0.042 ) ;

m = 2.177 e -26 kg   <---------ans

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