Answer to Question #66514 in Electricity and Magnetism for Chelsea

Question

There’s a flammable gas in the lab and nobody is sure whether it is methane (CH4),
ethane (C2H6), or propane (C3H8). Fortunately, you have a mass spectrometer (imagine
the luck!). The mass spectrometer uses an electric field of 1000 V/m and a magnetic
field of 0.500 T in the velocity selector, and this same magnetic field in the
deflection chamber. If the distance between the entry into the deflection chamber and
the location where the ion strikes the measurement plate (indicated in the diagram) is
2.49 mm, what is the mass for the material assuming that it is singly ionized? If 1 amu
= 1.66 × 10−27 kg, is the material methane (16 amu), ethane (30 amu), or propane (44
amu)?