1128_Physics ProblemsTechnical Physics

1128_Physics ProblemsTechnical Physics - Chapter 40 The...

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Chapter 40 469 P40.18 The energy needed is E == × 1 00 1 60 10 19 .. eV J. The energy absorbed in time interval t is Et I A t P ∆∆ so t E IA × ⋅× L N M O Q P = 160 10 282 10 128 10 148 19 15 2 7 . . . J 500 J s m m s d a y s 2 ej e j π . The gross failure of the classical theory of the photoelectric effect contrasts with the success of quantum mechanics. P40.19 Ultraviolet photons will be absorbed to knock electrons out of the sphere with maximum kinetic energy Kh f max =− φ , or K max . = ×⋅× ×× F H G I K J −= −− 6626 10 300 10 200 10 100 10 470 151 34 8 91 9 Js ms m eV 1.60 J eV eV e j . The sphere is left with positive charge and so with positive potential relative to V = 0 at r =∞ . As its potential approaches 1.51 V, no further electrons will be able to escape, but will fall back onto the sphere. Its charge is then given by V kQ r e = or Q rV k e ×⋅ 500 10 899 10 841 10 2 9 12 . . m N m C Nm C C 22 bg . P40.20 (a) By having the photon source move toward the metal, the incident photons are Doppler
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