The Photoelectric Effect

iitaspirant

it is difficult to solve some poblems in phpto electric effect

visioniit

its really not.try to understand the concepts.and well the formulas.actually photo electric effect is the easiest part.

nishant

nope...problems in photoelectric effect generally utilise einstein's photoelectric equation,so try practising the problems based on the equation and u will surely come out on tops...cheers!!

edison

NOT REALLY

Just remember the basic phenomena of photo electric effect along with a couple of formulae to crack the problems.

The brief theory along with important results is as below.

The photo electic effect signifies particle nature of light.

The Photoelectric Effect

The details of the photoelectric effect were in direct contradiction to the expectations of very well developed classical physics.

The explanation marked one of the major steps toward quantum theory.

The remarkable aspects of the photoelectric effect when it was first observed were:

	1. The electrons were emitted immediately - no time lag!
	2. Increasing the intensity of the light increased the number of photoelectrons, but not their maximum kinetic energy!
	3. Red light will not cause the ejection of electrons, no matter what the intensity!
	4. A weak violet light will eject only a few electrons, but their maximum kinetic energies are greater than those for intense light of longer wavelengths!

edison

Photoelectric Effect

Most commonly observed phenomena with light can be explained by waves. But the photoelectric effect suggested a particle nature for light.

edison

Laws of photoelectric emission

For a given metal and frequency of incident radiation, the number of photoelectrons ejected per second is directly proportional to the intensity of the incident light.
For a given metal, there exists a certain minimum frequency of incident radiation below which no emission of photoelectrons takes place. This frequency is called the threshold frequency.
Above the threshold frequency, the maximum kinetic energy of the emitted photoelectron is independent of the intensity of the incident light but depends only upon the frequency (or wavelength) of the incident light.
The time lag between the incidence of radiation and the emission of a photoelectron is very small, less than 10^-9 second.

Equations

In analysing the photoelectric effect quantitatively using Einstein's method, the following equivalent equations are used:

Energy of photon = Energy needed to remove an electron + Kinetic energy of the emitted electron

Algebraically:

$hf = \phi + E_{k_{max}} \,$

where

h is Planck's constant,
f is the frequency of the incident photon,
$\phi = h f_0 \$ is the work function, the minimum energy required to remove a delocalised electron from the surface of any given metal,
$E_{k_{max}} = \frac{1}{2} m v_m^2$ is the maximum kinetic energy of ejected electrons,
f₀ is the threshold frequency for the photoelectric effect to occur,
m is the rest mass of the ejected electron, and
$v m$ is the velocity of the ejected electron.

Note: If the photon's energy (hf) is not greater than the work function (

?

), no electron will be emitted. The work function is sometimes denoted

W

. According to Einstein's special theory of relativity the relation between energy (E) and momentum (p) of a particle is $E = \sqrt{(pc)^2 + (mc^2)^2}$ , where m is the rest mass of the particle and c is the velocity of light in a vacuum.

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The Photoelectric Effect

Photoelectric Effect

Laws of photoelectric emission

Equations