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Midterm_Fa 11_solutions

# Midterm_Fa 11_solutions - MatE 153 Fall 2011 Midterm...

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1 MatE 153 Fall 2011 Midterm Solutions ____ / 80 Total Points = _____% 1.) A tungsten wire (W) heats up to 80ºC during use. a. What is the resistivity of the wire at 80ºC? (10 points) ( ) [ ] ( ) m n m n T T T o o Ω = + Ω = = + = + = 8 . 69 273 353 202 1 1 50 273 80 1 0 ρ α ρ ρ b. What is the electron mobility at 80ºC? (10 points) s V m C s A A V m m electr C en en m electr cm electrons mol g mol atoms cm g atom electron M N density atom ctron valenceele n A A × = Ω Ω × × × = = = × = × = × = = = 2 4 9 3 29 19 3 29 3 23 23 3 10 53 . 3 10 8 . 69 10 53 . 2 10 6 . 1 1 1 10 53 . 2 10 53 . 2 84 . 183 10 02 . 6 3 . 19 / 4 / # ρ σ μ 2.) In a photoelectric effect experiment on silver (Ag) target, the measure stopping voltage was 7 eV. The intensity of light was 30 mW/m 2 . The work function of Ag is 4.26 eV. a. What was the wavelength of light used in the experiment? (10 points) nm m J s m Js E hc hc J eV J eV E eV eV eV E E KE light light light light 110 10 1 . 1 10 80 . 1 10 3 10 626 . 6 10 80 . 1 10 6 . 1 26 . 11 26 . 11 26 . 4 7 7 18 8 34 18 19 = × = × × × = = = × = × = = + = Φ = λ λ b. What was the momentum of the light?

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