Difference Between Electromagnetic Radiation And Thermionic Emmission
Electromagnetic Radiation, the transmission of energy in the form of paired electric and magnetic fields. The most familiar forms of electromagnetic radiation are light waves; heat, or infrared, radiation; and radio waves. However, the radiation also travels in shorter waves in the forms of ultraviolet light, X rays, and gamma rays. All of these forms of radiation have similar characteristics, including the velocity at which they travel.
Radiation in general is one of the three ways in which energy can be transmitted, the other two being convection, or transmission through the motion of physical particles, and conduction, or transmission through the transfer of mechanical energy from particle to particle. Electromagnetic radiation, on the other hand, does not depend on a material medium for transmission. Instead it takes place as a wave motion through space, although in some circumstances the radiation behaves as though it were composed of particles rather than waves.
Thermionic emission is the phenomenon by which electrons are emitted into a vacuum as a result of the thermal excitation, or heating, of a metal or oxide-coated conductor. The cathode of an electron tube, for instance, is a thermionic emitter, and an electron tube that relies for its current on a heated cathode—as do most vacuum tubes—is called a thermionic tube. Thermionic emission is also known as the Edison effect, because Thomas A. Edison discovered the phenomenon in 1883 while developing filaments for the electric lightbulb.