The three ways are:
(i) In a cathode ray tube, when pressure of 0.01mm of Hg and a high p.d. of about 10000V is applied across its electrodes.
(ii) In a diode-valve, it is produced from the heated cathode from where they are attracted by the anode plate kept at a high positive potential.
(iii) Electrons are also produced in the process known as ‘photo electric emission’ by focussing light on a metal surface coated with cesium oxide.
