- Heating or an electrical discharge at S produces the ions.
- The ions drift through S1 and are accelerated through a potential difference to S2.
- The velocity of the particle at S2 can be calculated by using:
qV = 1/2(mv2) Equation I
- Ions travelling with velocity v enter the magnetic field B which provides a centripetal force. This force can be calculated by using:
qvxB = (mv2)/r Equation II
- Rearranging equation I for velocity, substituting into equation II, and rearranging for mass gives:
m = (qB2r2)/2V Equation III
- The ions strike and expose a photographic film at point a.
- The radius of the circular path can be measured, and if the charge q, magnetic field strength B, and the accelerating potential V are known, equation III can be used to calculate the mass of the ion.
- Note that the larger the radius of the path, the more massive the ion. The particle that lands at b will be more massive than the one which lands at a.
- Many mass spectrometers use velocity selectors (electric and magnetic fields used simultaneously to permit only particles of a given velocity to travel on a straight path (See example before cathode ray tube above for a velocity selector).
- The mass spectrograph led to the discovery of isotopes.
- Isotopes - atoms of an element with different masses.
- have the same number of protons
- have the same number of electrons for a neutral atom
- have different numbers of neutrons.
January 17, 2014