TE Enriched Sample (E)

Photoelectric Effect 1 32 Exercise Take h = 6.63 × 10 −34 J s, e = 1.60 × 10 −19 C and c = 3 × 10 8 m s −1 . For other physical constants, see the Appendix. 1. The energy of a photon in a beam of red laser is directly proportional to the A. speed of the light. B. frequency of the light. C. wavelength of the light. D. intensity (brightness) of the light. 2. Certain radiation is directed onto a surface over a fixed area. If we increase the intensity while keeping its frequency unchanged, will the following increase? (a) The power delivered to the surface (b) The energy of each photon (c) The number of photons delivered to the surface per second 3. The human eye controls the amount of light that enters the eyeball by adjusting the size of the pupil. In bright light of intensity 1 W m −2 , the pupil has a diameter of about 3 mm. Assume that the wavelength of the light is 600 nm, estimate the number of photons that enter the eyeball per second. 4. Two identical surfaces are illuminated normally by radiation X of wavelength 100 nm and radiation Y of wavelength 200 nm, respectively. If the intensity of X is twice that of Y , what is the ratio of the number of photons hitting on the two surfaces? A. 1 : 1 B. 2 : 1 C. 3 : 2 D. 5 : 4 5. A beam of light falls on a piece of metal. Do the following depend on the frequency of the incident light? (a) The energy of the photon (b) The chance of getting photoelectron emission (c) The average KE of the photoelectron emission B yes no yes 2 × 10 13 A yes yes yes 6. Is Einstein’s photoelectric equation an illustration of the following physical laws? A. Newton’s third law of motion B. The conservation of momentum C. The conservation of energy D. The mass–energy relation E = mc 2 7. In a photocell experiment, the stopping potential V s plotted against the frequency f of the incident light is as shown. f / Hz 0 V s / V –4.7 Find (a) the slope of the graph. (b) the work function of the metal. (c) the threshold frequency for the metal. 8. (a) Briefly describe the concept of the photon. (b) State Einstein’s photoelectric equation and explain all the terms. 9. Explain the following features of the photoelectric effect using the concept of the photon. What are the problems of the wave theory of light on these features? (a) There is a threshold frequency below which no photoelectrons are emitted. (b) The maximum KE of the photoelectrons depends on the frequency of the radiation, not its intensity. 10. Light of wavelength 550 nm and intensity 5 Wm −2 is shone normally on the photoemissive surface of area 10 mm 2 in the photocell of a circuit. (a) Calculate the energy of a photon of this light. (b) Estimate the number of photons falling on the metal surface per second. C 4.14 × 10 −15 V s 4.7 eV 1.13 × 10 15 Hz K max = hf − φ 3.62 × 10 −19 J 1.38 × 10 14 (1.2) 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.