20111ee2_1_2011_EE2_HW2

# 20111ee2_1_2011_EE2_HW2 - 10 9 m-1 . At which speed does...

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Physics for Electrical Engineers Prof. B. Jalali EE 2 Homework #2 Due: Jan 27, 2011 You may or may not find the following information useful: h=6.626 × 10 -34 J-s Mass of the electron=9.1 × 10 -31 kg Speed of light in vacuum = 2.998×10 8 m/s Electronic charge = 1.602 × 10 -19 C 1. a. Show that the Fermi function is symmetric about E F , i.e., f ( E F + E )=1 - f ( E F - E ) b. Show that when ( E - E F ) 2 kT , f ( E ) exp E E kT F Actually, calculate f ( E ) for ( E - E F ) equal to 2 kT , 3 kT and 4 kT by using the Fermi function. Compare the results with those obtained by using the exponential approximation. 2. Suppose the energy of an electron is given by E ( k ) = 3.5 10 -38 k 2 Joules, where k is given in units of meters -1 . a. Find the effective mass, and give the ratio of the effective mass to the ordinary mass of the electron. b. Find the phase and group velocities of an electron whose k=7.8
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Unformatted text preview: 10 9 m-1 . At which speed does the electron actually travel? (Hint: use Google for the definition of phase velocity.) 3. Consider the one-dimensional example discussed in the class, with the atoms 0.3nm apart. a. If an electric field E equal to 100 V/cm acts on the electrons for a time interval of 10-13 sec, what will be the change in the k value of the electron? b. What would it be as a percentage of /a? 4. Figure 1 shows the solar spectral irradiance area (unit: W/m 2 nm) vs. different wavelengths (unit: nm) of a solar cell made out of Silicon (assume Eg=1.24eV). Calculate the percentage of the sun’s power that will be absorbed into the solar cell. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Spectral irradiance, W/(m nm) 2 500 1000 1500 2000 Wavelength, nm Figure 1...
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## This note was uploaded on 10/07/2011 for the course EE 2 taught by Professor Vis during the Spring '07 term at UCLA.

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