2018_H2_Quantum_Physics_Tutorial_(Teachers)

9749 H2 PHYSICS Tutorial Nanyang Junior College 1 Chapter 19 QUANTUM PHYSICS speed of light in free space c = 3.00 × 108 m s-1 elementary charge e = 1.60 × 10-19 C the Planck constant h = 6.63 × 10-34 Js unified atomic mass constant u = 1.66 × 10-27 kg rest mass of electron me = 9.11 × 10-31 kg rest mass of proton mp = 1.67 × 10-27 kg Self-Attempt Questions Photoelectric Effect 1 What provides evidence for the particulate nature of electromagnetic radiation? A Electrons can be diffracted by a carbon film. B Light can be diffracted by an obstacle. C Light from two coherent sources can produce an interference pattern. D Photoelectric emission occurs only for incident frequencies above a minimum value. 2 The figure below shows a setup used to investigate the photoelectric effect. When radiation of wavelength 225 nm is incident on the emitter, photoelectrons are emitted and a photocurrent is registered by the ammeter. Which of the following statements is true? A If the polarity of the p.d. source is switched around, photoelectrons will not be emitted anymore. B If radiation of a shorter wavelength is used, the ammeter will register a higher photocurrent. C If radiation of a longer wavelength is used, the ammeter will register a higher photocurrent. D If the intensity of the radiation is increased, the ammeter will register a higher photocurrent. A emitter collector incident radiation p.d. source

9749 H2 PHYSICS Tutorial Nanyang Junior College 2 Changing the wavelength of the radiation changes the KEmax of the electrons, it does not change the rate of emission of photoelectrons. Switching the polarity of the p.d. source will not prevent the emission of photoelectrons as long as the radiation is above the threshold frequency. Increase the intensity of radiation will increase the current as the rate of emission of photoelectrons will increase. 3 In a particular photoelectric experiment, it was found that when light of wavelength 187 nm is incident on the metal surface, the stopping potential is 2.70 V. What will be the stopping potential if light of wavelength 87 nm is used instead? A 1.70 V B 4.94 V C 10.3 V D No electrons will be emitted ( ) ( ) ( ) ( )( ) 8 34 19 9 19 3.0 10 6.63 10 1.6 10 2.7 187 10 6.32 10 J S ch eV φλ φ φ −− − − = + × × = +× × = × When wavelength is changed to 87 nm, ( )( ) ( ) ( ) 8 34 19 19 9 3.0 10 6.63 10 6.32 10 1.6 10 87 10 10.3 V S S V V − −− − × × = × +× × = 4 In a photoelectric emission experiment using light of a certain frequency, the maximum kinetic energy Ek of the emitted photoelectrons is measured. Which graph represents the way in which Ek depends on the intensity I of the light? A B C D In photoelectric effect, kinetic energy Ek is independent of the intensity I of light. Line Spectra 5 Which one of