PHOTOELECTRIC EFFECT:

The photoelectric effect involves, irradiating  a metal surface with photons of sufficiently high energy to eject the electrons  from the metal.

• The photoelectric effect occurs with photons having energies from a few  electronvolt to  over 1MeV.
• The photoelectric effect phenomena (convert light into electricity)  used to adjust the automatic Iris in various types of cameras,and; in solar cells.

• The concept of wave-particle duality was developed because of the photoelectric effect.

WORK FUNCTION: (W)

Work function is the minimum energy employed to remove an electron from the surface of a given metal. Work function is an intrinsic property of the metal.

Work function is similar to ionization energy, which is the energy required to knock out the electron from atom or molecule in the gaseous state.

Ionization energies for metals are considerable than the corresponding work functions.

PHOTON :

The electromagnetic wave itself is composed of the tiny quantum  packet of energy called photons.

Einstein suggested that each quantum of light are equal to the frequency multiplied by the constant called Planck’s constant.

PHOTON- PROPERTIES

• Discrete bundle of  electromagnetic energy.

• Travel at the vacuum speed of light.

• Behave like a particle and a wave simultaneously

• Have zero mass and rest energy

• Carry energy and momentum.

• Electrically neutral.

Photon whose energy E  can be transferred to an actual particle (an electron)  imparting kinetic energy to it, just in an elastic collision between two massive particles such as billiard balls.

Every photon of sufficient energy excites only one electron, increasing  lights intensity only increases the number of ejected electrons and not their kinetic energy.

There is an excess energy, beyond the work function W ,in the photon, the excess energy is converted into kinetic energy of electrons.

ENERGY OF  PHOTON:

EXPLANATION OF KINETIC ENERGY:    

Kinetic energy of the  emitted electron is linearly proportional to the frequency of  incident radiation above a threshold value.

EXPLANATION OF THE EFFECT OF INTENSITY:

The number of photoelectrons emitted (the photoelectric cuerrent) is proportional to the Intensity. (independent of the frequency of Incident radiation above threshold value).

EXPLANATION OF THRESHOLD FREQUENCY:

Below a certain frequency, the photoelectric effect does not occur at all. The threshold frequency is different for different materials . Visible light for  alkali metals, near UV for other metals,and extreme UV radiation for non-metals.

The threshold frequency or cut off  frequency, which is used to find the work function.

EXPLANATION OF TIME LAG:

The time between  the incidence and emission of  the photoelectron is very small, less than 10^-9 second.