Mass spectrometer is a device that - Identifies amount and type of chemicals pre
ID: 1345121 • Letter: M
Question
Mass spectrometer is a device that - Identifies amount and type of chemicals present by-measuring m/q and the abundance of ions. Shown below are the essentials of a commercial mass spectrometer. This device is used to measure the composition of gas samples, by measuring the abundance of species of different masses. An ion of mass m and charge q = +e is produced in source S, a chamber in which a gas discharge is taking place. The initially stationary ion leaves S, is accelerated by a potential difference Delta V> 0, and then enters a selector chamber, S_1, in which there is an adjustable magnetic field B_1, pointing out of the page and a deflecting electric field E, pointing from positive to negative plate. Only particles of a uniform velocity v leave the selector. The emerging particles at S_2, enter a second magnetic field B_2, also pointing out of the page. The particle then moves in a semicircle, striking an electronic sensor at a distance x from the entry slit. Express your answers to the questions below in terms of E = magnitude of E, e, x, m, B_2 = magnitude of B, and Delta V What magnetic field Bi in the selector chamber is needed to insure that the particle travels straight through? Find an expression for the mass of the particle after it has hit the electronic sensor at a distance x from the entry slitExplanation / Answer
a) Workdone on the particle, W = q*delta_V
Apply Work-energy throem
Workdone = change in kinetic energy
q*delta_V = 0.5*m*v^2
==> v = sqrt(2*q*delta_V/m)
when net force acting on particle is zero, it moves in a straight line.
Apply, Fe = FB
q*E = q*v*B1
B1 = E/v
= E/sqrt(2*q*delta_V/m)
= E*sqrt(m/(2*e*delta_V)) <<<<<<--------Answer
b) radius of the orbit, r = m*v/(B2*q)
x/2 = m*v/(B2*q)
x = 2*m*v/(B2*q)
= 2*m*sqrt(2*q*delta_V/m)/(B2*q)
= 2*sqrt(2*m/e)/2 <<<<<<--------Answer