(1) (a) The beam from a green laser pointer with lambda = 532 nm is 1 mm in diam

Question

(1) (a) The beam from a green laser pointer with lambda = 532 nm is 1 mm in diameter as it exits the laser. Roughly how big will the laser spot be on a screen 20 m away?

(b) What must be the minimum diameter of the primary mirror on an NSA spy satellite in low-Earth orbit (300 km up) in order to be able to read the letters on a license plate (assume its trying to resolve two points about 20 cm apart)? Assume lambda = 500 nm.

(c) Sirius A is the closest A-type main sequence (i.e., Sun-like) star to Earth, at a distance of 8.6 light years. Its diameter is roughly 2.3x10^9 m. What is the angle subtended by the diameter of Sirius, as viewed from the Earth? What size mirror would you need to resolve the diameter of Sirius? Assume lambda = 500 nm.

Explanation / Answer

1) a) 1 mm

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