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Quiz2CKey - Physics 135-3 Quiz#2C Key Spring 2008...

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Unformatted text preview: Physics 135-3 Quiz #2C Key Spring 2008 Instructions: Write your name on the back of this Sheet & do your work on then/ram. 1. At a certain point in space, at a certain instant of time, the magnetic field of a light wave points in the + x—direction and is given by BX 2 EM cos(kz + car). In which / y E direction does the wave travel? In which direction does the associated electric field X point? (2 pts.) B Direction wave travels: — z direction Direction of E: + y direction CD 2. The Earth (radius 6.4 X 106 m) orbits the Sun (power 3.83 X 1026 J/s) in a (roughly) circular orbit of radius 1.5 X 10“ 1n. Assuming that the Earth absorbs 60% of the incident solar radiation and reflects 40%, what force does the Sun’s radiation exert on the Earth? Be sure to include units with your answer. (8 pts) P 3.83 X 1026; , M. I ~ 2 — 2 = 1.35 X 103 T = intensity of sunlight at Earth ”Res 47r(1.5 X 10“ m) (0.6[)A (O.41)A , L4 7 . EM, 2 —C—— + 2—”— : (1.4) 7 where A : 75R]; “ Earth cross—sectional area C J/s (l.4)(l.35>< 103 —;r)7r(6.4>< 106 my 120,— 8 =8.1x108N ’0 3.00>< 10 m/s Force of Radiation on Earth = 8.1 X 108 N ...
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