sun.pdf - UNIVERSITY OF CALIFORNIA SAN DIEGO Electrical and...

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UNIVERSITY OF CALIFORNIA, SAN DIEGO Electrical and Computer Engineering Department ECE 120 - Spring 2013 Solar System Physics MIDTERM EXAM KEY Problem Weight Score 1 9 2 9 3 9 4 9 5 9 6 9 7 9 8 9 9 16 10 12 1. The primary energy source for the sun is (a) nu clear fu sion. (b) atomic fission. (c) gravity (d) pressure. 2. When we speak of the surface of the sun we are referring to the (a) solar corona. (b) pho to sphere. (c) chromosphere. (d) solar wind. 3. The magnetic field of the sun reverses sign (approximately) once every (a) year. (b) 5 years. (c) 11 years. (d) 27 years. 1
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4. The outer core of the Earth is best described as (a) a silicon and magnesium mix in a plastic state owing to the moderately high tem- peratures. (b) a nickel and iron mix in a solid state owing to the high pressure. (c) a nickel and iron mix that be haves like a low - vis cos ity fluid ow ing to the high tem per a ture. (d) a lower density aluminum and calcium mix resulting from the di ff erentiation of lighter compounds from the inner core. 5. In which of the following atmospheric regions is the ozone layer located: (a) troposphere (b) strato sphere (c) mesosphere (d) thermosphere 6. If an electromagnetic wave is transmitted towards the ionosphere at a frequency well above the plasma frequency, the wave will (a) prop a gate through the iono sphere into space. (b) be reflected by the ionosphere back towards the ground. (c) will be absorbed by the ionosphere and converted into heat. (d) will be trapped within the ionosphere. 7. The chromosphere is located (a) just above the solar core. (b) just above the pho to sphere. (c) at the outer reaches of the corona. (d) in Detroit. 8. Qualitatively explain what generates the Earth’s geomagnetic field. Provide some detail, but no equations are needed. Solution: The most widely accepted idea for the source of the Earth’s geomagnetic field is the dynamo theory. In this theory the fluid outer core can di ff erentially rotate and because of its composition (primarily nickel and iron) is electrically conducting. There results a dynamo generation qualitatively similar to that of the homopolar generator (discussed in class). 9. Assume that the Earth’s atmosphere is in hydrostatic equilibrium, so that dP/dz = ρ g , where P is the atmospheric pressure, ρ is the mass density, and g is the local gravitational constant. Pressure and mass density are related by the ideal gas law P = ρ KT/m , where T is the temperature, K is the Boltzmann constant, and m is the 2
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electronic mass. Finally, assume that at z = 0 (corresponding to the surface of the atmosphere) the pressure, temperature, and density are P 0 , T 0 , and ρ 0 , respectively. If the atmosphere behaves like an adiabatic one-dimensional gas, then we would expect that the ratio P/ ρ 3 will be a constant, independent of height. What is the variation of temperature with height for this model?
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