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Mass spectrometer
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Separates ions by mass using a B field.
Ions of velocity v enter a magnetic field and travel on semicircles of radius r = mv/(qB), landing at positions that identify their mass-to-charge ratios. Used to detect isotopes and molecules.
Carbon-12 vs carbon-14 are separated by about 17%.
Ions must be accelerated first.
In more detail
A mass spectrometer separates ions by their mass-to-charge ratio, using electric and magnetic fields. The radius of curvature in a magnetic field reveals the mass.
Real-world uses
- Chemists identify compounds and measure isotope ratios with mass spectrometers.
- Forensic labs use them to detect drugs and explosives.
- Chemists use a mass spectrometer to identify molecules by measuring how far their ions are bent in a magnetic field.
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Frequently asked questions
How is the mass found?
From the radius r = mv/(qB), once the speed and charge are known.
Why do we need a velocity selector?
To ensure all ions reaching the detector have the same speed, which keeps the measurement accurate.
How does the spectrometer separate masses?
Heavier ions have larger radii of curvature for the same speed, so they land at different positions on the detector.
Related topics in Magnetism & Induction
Cyclotron frequency · Helical motion · Velocity selector · Cyclotron · Force on a current-carrying wire · Force between parallel wires