velocity selector
Definition and meaning of velocity selector in chemistry.
A velocity selector is an analytical device that utilizes crossed electric and magnetic fields to allow only charged particles with a specific, uniform velocity to pass through undeflected.
In more detail
In this specialized device, a beam of charged particles enters a vacuum region where an electric field and a magnetic field are oriented strictly perpendicular to each other and perpendicular to the direction of particle motion. The electric field exerts a deflecting force in one transverse direction, while the magnetic field exerts a similar force in the exact opposite direction. For a charged particle to travel in a perfectly straight line through the selector, these two opposing forces must exactly balance each other. This balance only occurs at a very specific velocity defined mathematically by the simple ratio of the electric field strength to the magnetic field strength. Particles moving faster or slower than this exact velocity will be vertically deflected and absorbed by surrounding physical slits.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Operating Principle | Perfectly balanced electric and magnetic forces |
| Selected Velocity Formula | v = E/B |
In a mass spectrometer, a velocity selector is frequently used to filter an initial ion beam so that only those ions traveling at a uniform speed successfully enter the subsequent mass analyzer section.
Frequently asked questions
Does the mass or electrical charge of the particle affect the selectively chosen velocity?
No, the specifically selected passing velocity depends entirely on the ratio of the external electric and magnetic fields, making it completely independent of the moving particle's mass or internal charge.