Question

Explain the construction and working of a Bainbridge mass spectrometer. Also mention its use.

Answer 1

Hint: Bainbridge mass spectrometer is an equipment used for the accurate determination of atomic masses. Draw a neat schematic diagram of the spectrometer in order to make a clear cut idea. The instrument is having both the electric and magnetic field in use.

Complete step-by-step answer:
A beam of positive ions generated in a discharge tube is collimated into a fine beam using two narrow slits ${{S}_{1}}$ ​and ${{S}_{2}}$. This fine beam is entering into a velocity selector. The velocity selector permits the ions of a certain velocity to come out of it, due to the combined action of an electric and a magnetic field. The velocity selector is having two plane parallel plates ${{P}_{1}}$ ​and ${{P}_{2}}$, which creates a uniform electric field E and an electromagnet, to develop uniform magnetic field B. These two fields are at perpendicular to each other and to the direction of the beam.
The electric field and magnetic field are kept as the deflection produced by one field is balanced by the other, so that the ions will not be having any deflection within the velocity selector. Let E and B be the electric field intensity and magnetic induction respectively and q be the charge of the positive ion. The magnetic force will be equal to the electric force.
$qE=qvB$
$v= \dfrac{E}{B}$
Where $v$ the velocity of the beam.
Those ions having the velocity to pass out of the velocity selector enter the evacuated chamber D through slit ${{S}_{3}}$. These positive ions having the equal velocity are kept at a uniform magnetic field of induction B perpendicular to the plane of the paper. These ions are deflected in a circular path and finally strike the photographic plate.
Ions with different masses trace semi-circular paths of varying radii and create dark lines on the plate. Using the distance between the opening chamber and the dark line, radius can be found. Isotopic mass of the particles can also be found. Hence the question is completely answered.

Note: The material is bombarded with a beam of electrons so the atoms or molecules it includes will turn into ions. This process is known as ionization. The ions split into a spectrum, with each different kind of ion bent in different quantities in accordance to its mass and its electrical charge.