Advertisements
Advertisements
प्रश्न
The work functions for potassium and caesium are 2.25 eV and 2.14 eV respectively. Is the photoelectric effect possible for either of them if the incident wavelength is 5180 Å?
[Given : Planck’s constant = 6.63 x 10–34 J.s.;
Velocity of light = 3 x 108 m/s; 1 eV = 1.6 x 10–19 J]
Advertisements
उत्तर
Given: (W0)P = 2.25 eV = 2.25 x 1.6 x 10-19 J = 3.6 x 10-19 J,
(W0)C = 2.14 eV = 2.14 x 1.6 x 10-19 J = 3.424 x 10-19 J,
λ = 5180 Å = 5.18 x 10-7 m
To find: Will the photoelectric effect occur for either of these elements with λ = 5180 Å
Formula: W0 = hv0
`(W_0)_p=h(v_0)_p`
`(v_0)_p=(W_0)_p/h=(3.6xx10^-19)/(6.63xx10^-34)`
`(v_0)_p=5.430xx10^14 Hz`
Similarly
`(v_0)_c=(W_0)_c/h=(3.424xx10^-19)/(6.63xx10^-34)`
`(v_0)_c=5.164 xx10^14Hz`
The corresponding frequency is given by,
`v_2=c/lambda=(3xx10^8)/(5.18xx10^-7)=3/5.18xx10^15`
`v_2=5.792xx10^14Hz`
for potassium
`5.792xx10^14Hz>5.430xx10^14Hz`
`i.e, v_2>(v_o)_p`
Photoelectric emission will take place when light of wavelength λ is incident on it. For caesium,
`5.792xx10^14Hz>5.16xx10^14Hz`
`i.e, v_2>(v_o)_c`
Photoelectric emission will take place when light of wavelength λ is incident on it. For λ= 5180Å wavelength, both potassium and caesium will exhibit photoelectric emission.
APPEARS IN
संबंधित प्रश्न
The photoelectric current in a photoelectric cell can be reduced to zero by a stopping potential of 1.8 volt. Monochromatic light of wavelength 2200Å is incident on the cathode. Find the maximum kinetic energy of the photoelectrons in joules. [Charge on electron = 1.6 x 10-19 C]
Draw a neat labelled circuit diagram of experimental arrangement for study of photoelectric effect.
Write three characteristic features in photoelectric effect that cannot be explained on the basis of wave theory of light, but can be explained only using Einstein's equation.
Light of intensity ‘I’ and frequency ‘v’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when (i) the intensity of light is gradually increased. In each case, all other factors remain the same. Explain, giving justification in each case.
Light of intensity ‘I’ and frequency ‘v’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when (ii) the frequency of incident radiation is increased. In each case, all other factors remain the same. Explain, giving justification in each case.
Light of intensity ‘I’ and frequency ‘v’ is incident on a photosensitive surface and causes photoelectric emission. What will be the effect on anode current when the anode potential is increased? In each case, all other factors remain the same. Explain, giving justification in each case.
Draw a plot showing the variation of photoelectric current versus the intensity of incident radiation on a given photosensitive surface.
The graph shows the variation of stopping potential with frequency of incident radiation for two photosensitive metals A and B. Which one of the two has higher value of work-function? Justify your answer.
If the total energy of radiation of frequency 1014 Hz is 6.63 J, calculate the number of photons in the radiation. (Planck’s constant = 6.63 x 10–34 J.s.)
In an experiment of the photoelectric effect, the graph of maximum kinetic energy EK of the emitted photoelectrons versus the frequency v of the incident light is a straight line AB shown in Figure 6 below:
Find:
1) Threshold frequency of the metal
2) The work function of the metal.
3) Stopping potential for the photoelectrons emitted by the light of frequency `v = 30 xx 10^14 Hz`
A photosensitive surface emits photoelectrons when red light falls on it. Will the surface emit photoelectrons when blue light is incident on it? Give reason.
Draw a plot showing the variation of photoelectric current with collector potential for different frequencies but same intensity of incident radiation ?
What change will you observe if intensity of incident radiation is changed but the frequency remains the same?
A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :
On what factors does the number of emitted photoelectrons depend?
In photoelectric effect, why should the photoelectric current increase as the intensity of monochromatic radiation incident on a photosensitive surface is increased? Explain.
Calculate the momentum of a photon of energy 6 x I 0-19 J.
Two metals A and B have work functions 4 eV and 6 eV respectively. Which metal has a lower threshold wavelength for photoelectric effect?
State how will you use this graph to detennine the value of Planck's constant.
The phenomenon of photoelectric emission was observed by ______.
Consider an electron in front of metallic surface at a distance d (treated as an infinite plane surface). Assume the force of attraction by the plate is given as `1/4 q^2/(4πε_0d^2)`. Calculate work in taking the charge to an infinite distance from the plate. Taking d = 0.1 nm, find the work done in electron volts. [Such a force law is not valid for d < 0.1nm].
What are the electrons emitted when light falls on a material generally called?
During which experiments did Heinrich Hertz observe photoelectric emission?
In Hertz’s experimental investigation, how were electromagnetic waves produced?
What happened to high-voltage sparks across the detector loop when the emitter plate was illuminated with ultraviolet light from an arc lamp?
What must electrons near the metal surface overcome before they can escape?
