Write Einstein'S Photoelectric Equation and Mention Which Important Features in Photoelectric Effect Can Be Explained with the Help of this Equation. - Physics


Write Einstein's photoelectric equation and mention which important features in photoelectric effect can be explained with the help of this equation.

The maximum kinetic energy of the photoelectrons gets doubled when the wavelength of light incident on the surface changes from λ1 to λ2. Derive the expressions for the threshold wavelength λ0 and work function for the metal surface.

State two important features of Einstein's photoelectric equation.



Einstein's photoelectric equations is given by



Kmax = Maximum kinetic energy of the photoelectron

vmax = Maximum velocity of the emitted photoelectron

m = Mass of  the photoelectron  

ν = Frequency of the light radiation

ϕ0 = Work function

If ν0 is the threshold frequency, then the work function can be written as

 ϕ0 = hν0


The above equations explains the following results:

1.  If ν < ν0, then the maximum kinetic energy is negative, which is impossible. Hence, photoelectric emission does not take place for the incident radiation below the threshold frequency. Thus, the photoelectric emission can take place if ν > ν0.

2. The maximum kinetic energy of emitted photoelectrons is directly proportional to the frequency of the incident radiation. This means that maximum kinetic energy of photoelectron depends only on the frequency of incident light.

According to the photoelectric equation,



Let the maximum kinetic energy for the wavelength of the incident λ2 be K'max


 Form (i) and (ii), we have







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2014-2015 (March) Delhi Set 2


The energy of photon of wavelength X is_____ .

[h = Planck’s constant, c = speed of light in vacuum]

The threshold wavelength of silver is 3800Å. Calculate the maximum kinetic energy in eV of photoelectrons emitted, when ultraviolet light of wavelength 2600Å falls on it.

(Planck’s constant, h =6.63 x 1O-34J.s.,

Velocity of light in air, c = 3 x 108 m / s)

The momentum of a photon of de Broglie wavelength 5000Å is _______.

[Planck’s constant = 6.63 x10-34 J.s.]

When radiations of wavelength λ1 and λ2 are incident on certain photosensitive, such that E1 > E2 . Then Planck's constant 'h' is ......................... .

(C = Velocity of light).

The photoelectric threshold wavelength of a metal is 230 nm. Determine the maximum kinetic energy in joule and in eV of the ejects electron for the metal surface when it is exposed to a radiation of wavelength 180 nm.

[Planck’s constant : h = 6.63 * 10-34 Js, Velocity of light : C = 3 * 108 m/s.]

Find the value of energy of electron in eV in the third Bohr orbit of hydrogen atom.

(Rydberg's constant (R) = 1· 097 x 107m - 1,Planck's constant (h) =6·63x10-34 J-s,Velocity of light in air (c) = 3 x 108m/ s.)

Find the wave number of a photon having energy of 2.072 eV

Given : Charge on electron = 1.6 x 10-19 C,

           Velocity of light in air = 3 x 108 m/s,

           Planck’s constant = 6.63 x 10-34 J-s.

State two important properties of photon which are used to write Einstein’s photoelectric equation.

Define (i) stopping potential and (ii) threshold frequency, using Einstein’s equation and drawing necessary plot between relevant quantities.

A proton and a deuteron are accelerated through the same accelerating potential. Which one of the two has less momentum?

Give reasons to justify your answer.

Write its S.I. unit of (intensity of radiation)

Radiation of frequency 1015 Hz is incident on two photosensitive surface P and Q. There is no photoemission from surface P. Photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain these observations and find the value of work function for surface Q.

The work function for a metal surface is 2.2eV. If the light of wavelength 5000Å is incident on the surface of the metal, find the threshold frequency and incident frequency. Will there be an emission of photoelectrons or not? (c = 3 x 108 m/ s, 1eV = 1.6x10-19 J , h = 6.63 x 10-34 J.s.)

Einstein's photoelectric equation is:

a) `E_"max" = hlambda - varphi_0`

b) `E_"max"= (hc)/lambda  varphi_0`

c) `E_"max" = hv + varphi_0`

d) `E_"max" = (hv)/lambda + varphi_0`

With reference to the photoelectric effect, define threshold wavelength

 Write the basic features of photon picture of electromagnetic radiation on which Einstein’s photoelectric equation is based.

Write Einstein’s photoelectric equation.

According to Einstein’s model, the threshold frequency for a metal having work function ϕ0 is given by _________.

According to the Einstein’s model, stopping potential Vo for a metal having work function ϕ0 is given by ______.

Which of the following graphs correctly represents the variation of maximum kinetic energy (Ek) of photoelectrons with the frequency (𝜈) of the incident radiation?

Calculate the maximum kinetic energy of photoelectrons emitted by a metal (work function = 1.5 eV) when it is illuminated with light of wavelength 198 nm.

Plot a labelled graph of |Vs| where Vs is stopping potential versus frequency f of the incident radiation. State how will you use this graph to determine the value of Planck's constant?

A police van moving on a highway with a speed of 30 km/h fires a bullet at a thief's car speeding away in the same direction with a speed of 192 km/h. If the muzzle speed of the bullet is 150 m is, with what speed does the bullet hit the thief's car?

According to Einstein's photoelectric equation, the plot of the kinetic energy of the emitted photoelectrons from a metal Vs the frequency of the incident radiation gives as straight the whose slope:

A 200 W sodium street lamp emits yellow light of wavelength 0.6 µm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is:

Dimensions of ‘resistance’ are same as (where h is Planck's constant and e is charge):

Threshold frequency for photoelectric effect on sodium corresponds to a wave length 5000. Its work function is

Who indirectly determined the mass of the electron by measuring the charge of the electrons?

If the frequency of light in a photoelectric experiment is double the stopping potential will

If the energy of photon corresponding to a wavelength of 6000 A° is 3.32 × 10-19 J, the photon energy for a wavelength of 4000 A° will be

What is the momentum of photon of energy 3 mev in kg ms-1?

The emission of electron is possible

(i) A ray of light incident on face AB of an equilateral glass prism, shows minimum deviation of 30°. Calculate the speed of light through the prism.

(ii) Find the angle of incidence at face AB so that the emergent ray grazes along the face AC.

  1. Calculate the frequency of a photon of energy 6.5 × 10−19 J.
  2. Can this photon cause the emission of an electron from the surface of Cs of work function 2.14 eV? If yes, what will be the maximum kinetic energy of the photoelectron?


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