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Unformatted text preview: = =-m r L d d = 2.0 m b) All of the power from the laser falls in a circle of radius r m on the moon, so the average intensity is given by 2 6 2 m) (160 W 10 . 2 = = = m r P A P I I = 25 W/m c) BOTH The power of the laser determines the power that reaches the moon, and the wavelength determines the area over which it is spread. 2. a) METAL b) E F is the energy of the highest occupied state, measured from the bottom of the conduction band. E F = 24 eV 20 eV E F = 4 eV c) is the least energy needed to free an electron from the material. It equals the difference between the top of the wells and the Fermi energy. = 32 eV 24 eV = 8 eV d) m 10 150 m/s) 10 . 3 s)( J 10 63 . 6 ( 9 8 34-- = = = hc hf E ph E ph = 1.33 10-18 J = 8.3 eV e) YES The energy of the photon is greater than the work function of the material....
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