HW14%20solutions - Homework 14 solutions Physics 204...

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Homework 14 solutions Physics 204, morning summer 2008 Chapter 29 Problems 8,21,38,43 Chapter 30 Problems 18,15 8. REASONING AND SOLUTION The work function of the material (using λ = 196 nm) is found from W 0 = hf = hc / λ = 1.01 × 10 –18 J The maximum kinetic energy of the ejected electron is (using λ = 141 nm) KE max = hf W 0 = hc / λ W 0 = 3.96 × 10 –19 J The speed of the electron is then v m = = × × = × 2 2 3 96 10 9 32 10 19 5 KE J 9.11 10 kg m / s max 31 c h c h . . 21. REASONING AND SOLUTION The de Broglie wavelength λ is given by Equation 29.8 as λ = h / p , where p is the magnitude of the momentum of the particle. The magnitude of the momentum is p = mv , where m is the mass and v is the speed of the particle. Using this expression in Equation 29.8, we find that λ λ = = = × × × = × h mv v h m or 6.63 10 J s 1.67 10 kg 0.282 10 m 1 41 10 m s –34 –27 –9 3 c hc h . / 38. REASONING The energy of a photon of frequency f is, according to Equation 29.2, E hf = , where h is Planck's constant. Since the frequency and wavelength are related by f c = / λ (see Equation 16.1), the energy of a photon can be written in terms of the wavelength as E hc = / λ . These expressions can be solved for both the wavelength and the frequency.
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