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प्रश्न
Read the following paragraph and answer the questions.
| The figure shows the variation of photoelectric current measured in a photocell circuit as a function of the potential difference between the plates of the photocell when light beams A, B, C and D of different wavelengths are incident on the photocell. Examine the given figure and answer the following questions: |
- Which light beam has the highest frequency and why?
- Which light beam has the longest wavelength and why?
- Which light beam ejects photoelectrons with maximum momentum and why?
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उत्तर
(i) We know that the stopping potential and frequency are related as
V = `((hf - phi))/q`
Where Φ is the work function defined as the amount of energy needed to bind the electrons in the metals, hf is the energy of photons, and q is the charge.
This relationship leads us to the conclusion that the greater negative the stopping potential, the higher the frequency. As a result, curve B has the highest frequency and the largest negative stopping potential in the graph.
(ii) We all know that the connection between wavelength and frequency is inverse. The wavelength reduces as the frequency rises and vice versa.
As can be seen from the graph, C has the lowest frequency out of all the possible values since its stopping potential is the least negative. Therefore, the wavelength is largest when the frequency is lowest. C has the longest wavelength as a result.
(iii) Highest momentum means highest kinetic energy which can be calculated with the help of velocity.
kinetic energy = `1/2mv^2`
Relation to the momentum, p2 = 2m(K.E.)
If kinetic energy is maximum, then momentum will be maximum.
We know that the stopping potential and frequency are related,
Vq = (hf - Φ)
The maximum kinetic energy of the electrons equals the stopping voltage when measured in electron volt. We can consider Φ as the kinetic energy.
Kinetic energy is maximum when the frequency is maximum and in the above part we have seen that it is maximum for curve B, so momentum is maximum for curve B.
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संबंधित प्रश्न
The electric field associated with a light wave is given by `E = E_0 sin [(1.57 xx 10^7 "m"^-1)(x - ct)]`. Find the stopping potential when this light is used in an experiment on photoelectric effect with the emitter having work function 1.9 eV.
The figure is the plot of stopping potential versus the frequency of the light used in an experiment on photoelectric effect. Find (a) the ratio h/e and (b) the work function.
Explain how does (i) photoelectric current and (ii) kinetic energy of the photoelectrons emitted in a photocell vary if the frequency of incident radiation is doubled, but keeping the intensity same?
Show the graphical variation in the above two cases.
How would the stopping potential for a given photosensitive surface change if the intensity of incident radiation was decreased? Justify your answer.
Plot a graph showing the variation of photoelectric current, as a function of anode potential for two light beams having the same frequency but different intensities I1 and I2 (I1 > I2). Mention its important features.
Which apparatus measures photocurrent?
What does emitter plate C do when light falls on it?
What is used to change light frequency and study its effect on emission and electron energy?
Why does greater light intensity produce more emitted electrons?
When are photoelectrons emitted in relation to the threshold frequency?
