TE Enriched Sample (E)

Summary 35 Failure of classical wave picture • Expects a time delay for energy accumulation before electrons are emitted ✗ • Expects emission of electrons to occur at any frequency ✗ • Expects electrons with higher KE to be emitted when the metal is illuminated by more intense light ✗ Keywords Classical theory vs quantum theory classical wave theory Einstein’s quantum theory • energy is accumulated continuously • rate of energy transfer depends on light intensity L only • frequency f plays no role in photoemission • one photon ( hf ) for one emission • intensity L = N × hf N : no. of photons (per second per m 2 ) hf : energy of each photon 1. condition for emission a energy transfer depends on intensity • occurs at any frequency ✗ • occurs if high enough intensity ✗ a one photon ( hf ) for one emission and K max = hf − hf 0 • occurs above the threshold frequency ✓ • occurs if hf > φ (= hf 0 ) ✓ • independent of intensity if f < f 0 ✓ 2. rate of emission a energy transfer depends on intensity • emission rate increases with intensity ✓ a intensity L = N × hf • emission rate increases with no. of photons per second ✓ 3. max KE of photoelectrons a energy transfer depends on intensity alone • K max increases with intensity ✗ • K max independent of frequency ✗ a one photon ( hf ) for one emission • K max increases with hf ✓ • K max = hf − z ✓ • K max independent of intensity ✓ 4. emission time a energy spreads on wavefront, so each electron gets little energy • emission delays for energy accumulation ✗ • emission delays longer at low intensity ✗ a absorption of photon is immediate • emission is immediate ✓ • emission time is independent of intensity and hf ✓ a node 陽極 cathode 陰極 Einstein ’ s photoelectric equation 愛因斯坦光電方程 electronvolt 電子伏特 photocell 光電池 photoelectric current 光電流 photoelectric effect 光電效應 photoelectron 光電子 photon 光子 Planck constant 普朗克常數 quantize 量子化 quantum 量子 quantum theory of light 光量子理論 stopping potential 遏止電勢 threshold frequency 臨閾頻率 work function 功函數 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.