Photoelectricity Introduction Planks hypothesis Properties of photons Photo

Photo-electricity §Introduction §Plank’s hypothesis §Properties of photons, §Photo electric effect §Laws and characteristics of photoelectric effect §Einstein’s photoelectric equation (simple problems) § Construction and working of photoelectric cell §Applications of photoelectric cell

Introduction • Photo-electricity is a branch of physics which deals with the study of photo-electrons • In 1897, J. J. Thomson discovered a negatively charged particles named electrons. • He discovered that charged particles are emitted by a metal surface when exposed to ultraviolet light • When ultraviolet rays falls on the metal surface (zinc plate), negatively charged particles emitted. These negatively charged particles are named as an electrons.

Plank’s hypothesis

Characteristics of Photoelectric Effect:

Photoelectric Effect

Electron Volt (e. V):

Einstein’s Photoelectric Equation

Photoelectric Cell: • Principle: The working of photoelectric cell is based on the principle of photoelectric effect. It converts light energy into electrical energy.

Engineering Applications of Photo Electric Cell: • The applications of photo-electric cell in engineering are listed as follows • (1) Burglar alarm • (2) Counting machines • (3) Lux meter I illumination meter • (4) Fire alann • (5) Opening and closing a door • (6) Automatic operation of water taps • (7) Street light control