Advertisements
Advertisements
Question
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.)
Advertisements
Solution
Given work function = `Φ_0` = 2.2 eV
= `2.2 xx 1.6 xx 10^(-19) J`
= `3.52 xx 10^(-19)`
λ = 500 Å = 5000 x 10-10 m, c = `3xx10^8` m/s, h = `6.63 xx 10^(-34) Js`
Incident frequency v = `c/λ = (3xx10^8)/(5000 xx 10^(-10)`
= `(3xx10^8)/(5xx10^(-7) )= 3/5 xx 10^(-15) Hz`
=`30/5 xx 10^(14) Hz = 6 xx 10^(14) Hz`
Threshold frequency v0 = `Φ_0/h = (3.52 xx 10^(-19) J)/(6.63 xx 10^(-34) Js`
= `0.53 xx 10^15 Hz = 5.3 xx 10^14 Hz`
Emission of photoelectron takes place only if incident frequency is greater than the threshold frequency. But, in this case n>n0 therfore, photoelectric emission takes place.
APPEARS IN
RELATED QUESTIONS
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.]
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 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.
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.
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.
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`
According to Einstein’s model minimum energy needed for the electron to escape from a metal surface having work function ϕ0, the electron is emitted with maximum kinetic energy, Kmax = ______.
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 ______.
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 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:
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
The slope of frequency of incident light and stopping potential for a given surface will be
What will be wavelength of a photon of momentum 6.6 × 10–24 kgms–1?
What is the momentum of photon of energy 3 mev in kg ms-1?
Which of the following is/are true for cathode ray
The emission of electron is possible
The wavelength of matter is independent of
The moment of a photon is given by
(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.
- Calculate the frequency of a photon of energy 6.5 × 10−19 J.
- 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?
Ultraviolet light is incident on metals P, Q and R, having work functions 8 eV, 2 eV and 4 eV respectively,
- Which metal has lowest threshold frequency for photoelectric effect?
- For which metal is the value of Emax minimum?
(Note: Emax is maximum kinetic energy of the emitted photoelectrons.)
The graphs below show the variation of the stopping potential VS with the frequency (ν) of the incident radiations for two different photosensitive materials M1 and M2.
Express work function for M1 and M2 in terms of Planck’s constant(h) and Threshold frequency and charge of the electron (e).
If the values of stopping potential for M1 and M2 are V1 and V2 respectively then show that the slope of the lines equals to `(V_1-V_2)/(V_(01)-V_(02))` for a frequency,
ν > ν02 and also ν > ν01
