Charge to Mass Ratio


The charge to mass ratio is used to find out what a unknown substance is. Each charge to mass ratio is unique for each kind of element. The charge to mass ratio or (q/m) was first found by Thomson by his experiments with cathode rays. This discovery made it possible for scientists to figure out what an substance is by using a mass spectrometer. By using the formula q/m = v/rB you can find the c/m, v being the velocity of the particle, r the radius of circular motion and B being the magnetism field. Using the q/m to find out what the particle is, is like using a fingerprint to find a person, it is unique for every element.
masspec.GIF
The picture above is the mass spectrometer which is used to calculate the q/m and then by using the q/m can find what the particle is.
You can find the Charge to mass ratio by using the table of elements. By dividing the charge by the atomic mass in kg, and the charge using 3+, 2+, 2-, ect. multiplied by the elementary charge. If this number is the same as the number from the mass spectrometer you have found your element.
References

  1. Jim Clark, 2000, http://www.chemguide.co.uk/analysis/masspec/howitworks.html
  2. Brad Langdale, 2012, http://ldindustries.ca/LDIndustries/P30/UnitB/12_-_Applications_of_Particle_Deflection.pdf