TE Enriched Sample (E)

The quantum theory of light 33 1.2 (c) If only 2% of the photons can cause the emission of photoelectrons, estimate the photocurrent produced, assuming that all the photoelectrons can reach the anode of the photocell. 11. When light of frequency 10 15 Hz is shone on a photocell, the stopping potential is measured to be 0.5 V. (a) Find the work function and threshold frequency of the photoemissive surface of the photocell. (b) Find the stopping potential when light of frequency 2 × 10 15 Hz is used. 12. The threshold wavelength λ 0 is the wavelength that corresponds to the threshold frequency. Ametal surface has a threshold wavelength of 650 nm. Given the mass of an electron is 9.11 × 10 −31 kg. (a) Calculate its threshold frequency. (b) Calculate its work function in eV. (c) If the surface is illuminated by light of wavelength 400 nm, calculate (i) the stopping potential and (ii) the maximum speed of the photoelectrons (in terms of c ). (d) What will happen if light of wavelength 700 nm is used instead? Why? 13. The following graph shows how the stopping potential V s varies with the frequency f of the light falling on the cathode of a photocell. f / 10 14 Hz 1 10 12 14 0 2 3 16 V s / V (d) 4.42 × 10 −7 A 5.83 × 10 −19 J; 8.79 × 10 14 Hz 4.64 V 4.62 × 10 14 Hz 1.91 eV 1.20 V 2.16 × 10 −3 c no photoelectron emission (a) What is the threshold frequency for the metal of the cathode? (b) Calculate the maximum KE of the photoelectrons when the frequency of the incident light is 1.3 × 10 15 Hz. (c) Use this graph to estimate the Planck constant and find the work function of the photocell. (d) Sketch on the V s – f graph when another photocell with a photoemissive plate of work function 5 eV is used instead. 14. A photocell is illuminated by ultraviolet radiation of wavelength 300 nm. The photocurrent I P is plotted against V which is the potential of the anode relative to the photoemissive plate in the photocell. 0 0.6 I P / μA V / V -1.6 (c) (a) Find the work function of the photoemissive plate of the photocell. (b) The frequency of the radiation is doubled but the intensity is unchanged. Assume the percentage of photons that induce emissions is the same for different frequencies. Find the new stopping potential. (c) This time, the intensity of the radiation is increased while keeping the frequency unchanged. Using the analysis in (b), sketch the expected I P −V graph on the above diagram. 10 15 Hz 1.99 × 10 −19 J 6.67 × 10 −34 J s; 6.67 × 10 −19 J 4.07 × 10 −19 J 5.74 V Sample © United Prime Educational Publishing (HK) Limited, Pearson Education Asia Limited 2023 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publishers.

RkJQdWJsaXNoZXIy ODY0MTQz