# Einstein’s Photoelectric Equation and Laws of Photoelectric Equation

**Einstein’s photoelectric equation: **Einstein gave an explanation for photoelectric emission based on the Planck’s quantum theory of light.

When light of certain frequency (greater than threshold frequency) incidents on a metallic surface the energy on incident photon (hf) is:

- Partly used to eject the electron from surface.
- Partly remains as kinetic energy of ejected electrons.

i.e. Energy of photon = Work Function + Kinetic Energy of Electrons

or, $${hf = \phi + \text{Kinetic Energy} }$$

$${hf = hf_{\circ} + \text{Kinetic Energy}}$$

$$\frac{ch}{\lambda } = \frac{ch}{\lambda_\circ } = \frac{1}{2}mv^{2}$$

Where, h = Planck’s constant = 6.63×10^{-34 }Js

**Laws of photoelectric emission: **

- There exists a minimum frequency of incident light below which photoelectric emission is no possible. The frequency is called threshold frequency.
- A part of energy of incident electrons is used to eject electrons from a surface and remaining as kinetic energy of the ejected electrons.
- Increase in intensity of light increases the number of photoelectron.
- Increase in frequency of light increases the kinetic energy of electrons.

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