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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER

Causes of cathode ray emmission

Properties of cathode rays

Photon

Photoelectric effect

Work function

Threshold frequency

Threshold wavelength

Laws of photoelectric effect

Effect of intensity of incident light on photoelectric current

Effect of potential on photoelectric current

Effect of frequency on photoelectric current

Photoelectric emission is an instantaneous process

Failure of wave theory in explaining photoelectric effect

Einstein’s photoelectric equation: energy quantum of radiation

Particle nature of light

Wave nature of matter

Heisenberg’s uncertainty principle

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER

Cathode rays

Cathode rays are the stream of fast moving electrons.

The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by

(i) Thermionic emission: By suitably heating, sufficient thermal energy can be imparted to the free electrons to enable them to come out of the metal.

(ii) Field emission: By applying a very strong electric field (of the order of 108 Vm–1) to a metal, electrons can be pulled out of the metal, as in a spark plug.

(iii) Photo-electric emission: When light of suitable frequency illuminates a metal surface, electrons are emitted from the metal surface. These photo(light)-generated electrons are called photoelectrons.

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