CONCEPT MAP

The unit's concept map is rooted at 'Dual nature of radiation and matter' and branches into three major limbs that mirror the unit's own three sections. The Electron emission limb splits into the four named types -- thermionic, field, photoelectric and secondary emission -- with photoelectric emission itself flowing directly into the second, much larger limb. The Photoelectric effect limb gathers together the historical observations of Hertz, Hallwachs and Lenard; the three experimental studies of intensity, potential difference and frequency; the concept of quantization of energy; Einstein's photoelectric equation; and photocells and their uses -- tracing the exact path the unit itself follows, from puzzling observation through systematic measurement to quantum explanation to practical device. The Matter waves limb covers the de Broglie hypothesis and equation, the de Broglie wavelength of the electron, the Davisson-Germer experiment that confirmed it, and the electron microscope that exploits it. A fourth limb, X-rays, covers their introduction and production, and splits further into continuous and characteristic X-ray spectra together with their applications. Read as a whole, the map traces one continuous intellectual arc: radiation is sh …