TABLE OF CONTENTS An electron is treated to be a point mass particle. Its motion in uniform electric fields can be described through simple mathematical equations. The treatment is valid even when a large number of electrons or other charged particles are moving together in uniform fields. However, in many of the practical cases the electric fields happen to be non-uniform. The analysis of electron motion in such non-uniform fields is not easy to carry out and poses serious mathematical difficulties. Fortunately, there is a close resemblance between the motion of electrons in an electrostatic field and the propagation of light in a transparent medium. Light rays travel along a straight path in homogeneous media and along curved paths in non-homogeneous media. Light suffers refraction at an optical boundary. Similarly, electrons travel along straight lines in an equipotenrial region and follow a curved path in passing through points of varying potential. Electron paths deviate in moving from the region of one potential into the region of another potential very much like the refraction of light rays. The resemblance suggests that the concepts of geometrical optics can be applied to the motion of electrons in homogeneous and in non-homogeneous electric fields. The approach becomes highly useful in case of electron motion in non-uniform fields. Such an extension of the concepts of geometrical optics to electron motion is known as electron optics. Electron optics had its beginning in the works of H. Busch in 1926 and C. J. Davisson and C. J. Calbick...
