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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

Laws of photoelectric effect

  1. Effect of frequency on photoelectric current

    The stopping potentials are in the order V03 > V02 > V01 if the frequencies are in the order ν3 > ν2 > ν1. That is greater the frequency of incident light, greater is the maximum kinetic energy of the photoelectrons. Consequently, we need greater retarding potential to stop them completely.

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    Threshold frequency

    For a given photosensitive material, there is a certain minimum cut-off frequency, called threshold frequency, below which there is no emission of photoelectrons takes place, no matter how intense the incident light is.

    Above the threshold frequency, the stopping potential or equivalently the maximum kinetic energy KE of the emitted photoelectrons increases linearly with the frequency of the incident radiation, but is independent of its intensity.

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