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प्रश्न
Define the terms (i) ‘cut-off voltage’ and (ii) ‘threshold frequency’ in relation to the phenomenon of photoelectric effect.
Using Einstein’s photoelectric equation shows how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph.
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उत्तर
When light of sufficiently small wavelength is incident on a metal surface, electrons are ejected from the metal. This Phenomenon is called the photoelectric effect.
(i) The cathode is illuminated with light of some fixed frequency v and fixed Intensity I1. A small photoelectric current is observed due to few electrons that reach anode just because they have sufficiently large velocity of emission. If we made the potential of the anode negative with respect to cathode then the electrons emitted by cathode are repelled. Some electrons even go back to the cathode so that the current decreases. At a certain value of this negative potential, the current is completely stopped. The least value of this anode potential which just stops the photocurrent is called cut off potential or stopping potential.
(ii) For a given material, there is a certain minimum frequency that if the incident radiation has a frequency below this threshold, no photoelectric emission will take place, howsoever intense the radiation may be falling.
(iii) According to Einstein’s photoelectric equation, maximum K. E is given as
`K.E_(max) =(hc)/lambda phi = hv -phi`
Where λ is wavelength and ν is corresponding frequency and Φ is work function.
We expose a material to lights of various frequencies and thus photoelectric current is observed and cut off potential needed to reduce this current to Zero is noted. A graph is plotted and that is straight line.
At ν0 the stopping potential is zero this means at this frequency the incident light is not able to eject electrons this is threshold frequency. Extended this line gives the cut off potential to make the photo
current zero which is `(-phi)/e`
संबंधित प्रश्न
In an experiment on the photoelectric effect, the slope of the cut-off voltage versus the frequency of incident light is found to be 4.12 × 10−15 Vs. Calculate the value of Planck’s constant.
The work function for a certain metal is 4.2 eV. Will this metal give photoelectric emission for incident radiation of wavelength 330 nm?
In an accelerator experiment on high-energy collisions of electrons with positrons, a certain event is interpreted as annihilation of an electron-positron pair of total energy 10.2 BeV into two γ-rays of equal energy. What is the wavelength associated with each γ-ray? (1BeV = 109 eV)
Plot a graph showing the variation of photoelectric current with collector plate potential at a given frequency but for two different intensities I1 and I2, where I2 > I1.
Is p − E/c valid for electrons?
In a photoelectric experiment, the collector plate is at 2.0 V with respect to the emitter plate made of copper (φ = 4.5 eV). The emitter is illuminated by a source of monochromatic light of wavelength 200 nm. Find the minimum and maximum kinetic energy of the photoelectrons reaching the collector.
How does one explain the emission of electrons from a photosensitive surface with the help of Einstein’s photoelectric equation?
Choose the correct answer from given options
Photons of frequency v are incident on the surface of two metals A and B of threshold frequency 3/4 v and 2/3 v, respectively. The ratio of maximum kinetic energy of electrons emitted from A to that from B is
The minimum energy required to remove an electron is called ______.
A student performs an experiment on photoelectric effect, using two materials A and B. A plot of Vstop vs ν is given in Figure.
- Which material A or B has a higher work function?
- Given the electric charge of an electron = 1.6 × 10–19 C, find the value of h obtained from the experiment for both A and B.
Comment on whether it is consistent with Einstein’s theory:
