InterviewSolution
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InterviewSolution
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(a) describe briefly three experimentally observed features in the phenomenon of photoelectriceffect. (b) Discuss briefly how wave theory of light cannot explain these features. OR (a) Writethe important properties of photons which are used to establish Eintein's photoelectric equation . (b)Use this equationto explain the concept of (i) threshouldfrequencyand (ii) stopping potential .3. |
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Answer» Solution :(a) Einstein's photoelctric equation is `E_(k) =hv-W` for single photon. (i)Explanation of frequency Law :when frequency of incident photon (v). Incceases, the kinetic energy of emitted electron increases. Intensity has no effect on kinetic energy of photoelectrons. (ii) Explanation of Intensity Law :when intensity of incidentlight increases, the number of incident photons increases, as one photon ejects on electron , the increases in intensity will increase the number of ejected electrons. in other words, photocurrent will increase of intensity.Frequencyhas no effect on photocurrent . (iii) Explaantion of no time Lag Law : When the energy of incident photon is greater than work function, the photoelectron is immediately ejected. Thus, there is no time between incidence of light and emission of photoelectrons. (b) The wave theory of light could not explain the observed characteristics of photolectric effect. Einstein EXTENDED plank's quantum idea of light of explain photoelectric effect. OR (a) Importnt properties of photon which are used to establish Einstein's photoectric equation are : (i) it is a STABLE elementary paraticle of zero charge and spin equal to one. (ii)It travels with the speed of light. (iii) it is the exchange paraticle in electromagetic force. (iv) Absorption of photons by atoms and molecules can CAUSE excitation and ionisation. Ithas particle nature. (b) Einstein's photoelectric equation is . `hv= W + E_(k)` where, hv= energy of incident photon. W= Work function of PHOTOMETAL. `E_(k)`= K.E. of photoelectrons. For threshold frequency and stopping potential. The equation `K_(max) = 1/2 m V^(2)_(max) = ho - phi_(0) ` is called Einstein,s photoelectric equation. (i) Threshold frequency : for a given photosensitive material, there is a certain minimum frequency of the incident radiations below which no emission of photoelectrons place. This frequency is called thsehold frequecy `(B_(0))` (ii) Stopping potential: The minimum negative potential given to ANODE in a photo-cell for which the photo-electric current befcomes is zero is called stopping potenial. It is denoted by `V_(0)` |
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