The electron microscope, its development, The electron microscope, its development, present performance and future possibilities electronmicrosco00gabo Year: 1948 8 The Electron Microscope That is, the angular momentum changes proportionally to the magnetic flux which passes between the tzvo coaxial circles drawn through the initial and final positions respectively. This result can be put into an even simpler form if we intro- duce the vectorpotential A, from which the vector H of the magnetic field intensity can be derived by the operation H = curl A. In the case of axially symmetrical field
The electron microscope, its development, The electron microscope, its development, present performance and future possibilities electronmicrosco00gabo Year: 1948 8 The Electron Microscope That is, the angular momentum changes proportionally to the magnetic flux which passes between the tzvo coaxial circles drawn through the initial and final positions respectively. This result can be put into an even simpler form if we intro- duce the vectorpotential A, from which the vector H of the magnetic field intensity can be derived by the operation H = curl A. In the case of axially symmetrical fields the vector A has always tangential direction, therefore, we can write it in the following as a scalar quantity, A. This is connected with the magnetic flux M by the simple relation M = 27rrA (3) Fig. 2. Electron trajectories in magnetic lens. Curves orthogonal to the trajectories are drawn to show the variation of the pitch The magnetic field lines, , the meridian curves of the tubes which carry a constant flux ]\I have therefore equations rA =^ const. Their shape is shown in an example in the upper part of figure 3. The equation (2) becomes now e r(mvt — —A) = const. (4) The expression in brackets can be interpreted as the total momentum of the electron in the magnetic field. It consists of the mechanical momentum mz\ and a term of electromagnetic . . e origm,—-A. (K. Schwarzschild, 1903.) Familiarity with this concept is a great help in understanding the somewhat compli- cated motion of electrons in magnetic fields.
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