For the following questions, it may be useful to know that: Radius of the Earth:

Question

For the following questions, it may be useful to know that: Radius of the Earth: Radius of the Sun: Re = 638 106 m Rs = 6.96 x 108 m RES = 1.50 × 1011 m Earth's orbital radius (average): 1) Solar radiation at Earth's orbit has an average intensity of 1,368 W/m2 What is the average power transmitted by the sun? 2) What is the average force exerted on the surface of the earth by radiation pressure assuming all solar radiation is absorbed? (In reality, about 1/3 of this radiation is reflected back into space.) Approximate the cross sectional area of the earth as a circle. For comparison, the gravitational force between the earth and sun is 3) The Voyager 1 spacecraft is the farthest man-made object from Earth. It is currently 2.10 x 1013m from the sun. What is the force exerted on its high gain antenna (radius 1.85m) by solar radiation pressure? (Assume all light is reflected. Remember that the solar intensity will be less than at Earth.) 4) Unpolarized light with intensity 7.95 W/m" is incident upon two polarizers. The first has its polarization axis at a 37" angle from horizontal, while the second has its polarization axis at a 157" angle from horizontal. What is the intensity and polarization axis of the light after it has passed through both polarizers?

Explanation / Answer

1) I = P / (4 pi r^2)

P = (1368) (4 x pi x (1.50 x 10^11)^2)

P = 3.87 x 10^26 Watt  

2) Power on earth = (1368) (pi (6.38 x 10^6)^2)

= 1.75 x 10^17 W

F = (1/3)(2 P / c) + (2/3)(P/c)

F = (4/3)(1.75 x 10^17 / 3 x 10^8)

F = 7.77 x 10^8 N

3) P = (3.87 x 10^26 / (4pi)(2.10 x 10^13)^2) (pi 1.85^2)

P = 3 W

F = 2 p / c = 1 x 10^-8 N  

4) I1 = 7.95/2 = 3.975 W/m^2

If = I1 cos(157-37)^2 = 1 W/m^2 .....Ans

polarization axis- > 157 deg from horizontal.

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