Please explain "inducing electric field" which I found from reading about magnetron and klystron. This is what I found from a book. Magnetron: e- from cathode, forced by the pulsed voltage, go to the anode (in a sweeping motion due to mag. field) induce oscillating electric field at the ends of the anode opening. Klystron: e- from the e-gun gets bunched in the initial buncher cavity and drifts to the catcher cavity where it induces retarding electric field (which forces the e- to slow down and the loss of KE is given off as microwave) Why/how does electrons approaching something "induce" electric field. And why for the magnetron the book says "oscillating E field" and for Klystron "retarding E field" Thank you.