THE+QUANTUM+NATURE+OF+RADIATION

IB PHYSICS > QUANTUM AND NUCLEAR PHYSICS =THE QUANTUM NATURE OF RADIATION= Describe the photoelectric effect



PHOTOELECTRIC EFFECT: When light shines on a clean metal surface, electrons are emitted from the surface.

BUT: Below a particular frequency of light there is no photoelectric effect; There is an effect however dim the light;

 THRESHOLD FREQUENCY (f 0 ): Below this frequency, no photoelectrons are emitted. Also, the intensity of the incident light is proportional to the number of electronS emitted.

This phenomenon is not consistent with the idea of light as a wave. Einstein proposed that the iNcident light should be considered as packets of light.

Describe the concept of the photon, and use it to explain the photoelectric effect. PHOTON: Packet of light energy. Energy is proportional to frequency of light.

Students should be able to explain why the wave model of light is unable to account for the photoelectric effect, and be able to describe and explain the Einstein model



Describe and explain an experiment to test the Einstein model. Millikan’s experiment involving the application of a stopping potential would be suitable.

STOPPING POTENTIAL: The opposing PD necessary to stop photo-electron current. A measure of the maximum KE of electrons.  WORK FUNCTION ( f ): Minimum energy required for electrons to escape from a particular metal surface. Photoelectrons are released by photons with energy hf. The extra energy is kinetic energy of the photoelectron

Solve problems involving the photoelectric effect.