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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

Wave nature of matter

The wave nature of light shows up in the phenomena of interference, diffraction and polarisation. On the other hand, in photoelectric effect and Compton effect which involve energy and momentum transfer, radiation behaves as if it is made up of a bunch of particles – the photons.

The gathering and focusing mechanism of light by the eye-lens is understood in the wave picture.

But its absorption by the rods and cones (of the retina) requires the photon picture of light.

Louis Victor de Broglie suggested that moving particles of matter should display wave-like properties under suitable conditions. He reasoned that nature was symmetrical and that the two basic physical entities – matter and energy, must have symmetrical character. If radiation shows dual aspects, so should matter.

???

De Broglie proposed that the wave length λ associated with a particle of momentum p is given as

λ =hp= hmv

where m is the mass of the particle and v its speed.

Now if V is the magnitude of accelerating potential in volts,

But  K  =12 mv2=p22m

 p=2mK=2m eV 

λ  =hp=h2mK=h2m eV=1.227V nm

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