2. Describe how to make a retroreflector, what a retroreflector does, and two ap

Question

2. Describe how to make a retroreflector, what a retroreflector does, and two applications of retroreflectors. (Retroreflectors are discussed in our textbook.) 3. When you look up at night the stars appear to be twinkling. a) Explain the role of refraction in the apparent twinkling of the stars. (You may need to Google this question. Many student give an incomplete explanation. Be sure to discuss the role of “fluctuations" or "turbulence") b) You generally do not see planets twinkling when you look up at them. Why not?

Explanation / Answer

Problem 2)

A retroreflector is a device or surface that reflects light back to its source with a minimum of scattering. In a retroreflector an electromagnetic wavefront is reflected back along a vector that is parallel to but opposite in direction from the wave's source. The angle of incidence at which the device or surface reflects light in this way is greater than zero, unlike a planar mirror, which does this only if the mirror is exactly perpendicular to the wave front, having a zero angle of incidence.

Retroreflectors with Glass Beads:

Any surface that can be painted can be made retroreflective by sprinkling glass beads onto freshly applied paint.

How to Make an Open Corner Cube Retroreflector

A simple retroreflector can be made from 3 mirrors arranged to form the corner of a cube. You’ll need three 2×2 glass mirrors, double-sided tape, and a standard 2-1/8×2-1/8×4-1/8 plastic box. Use care working with small mirrors, as they have sharp edges and are easily broken; supervise children. Follow these steps:

1. Clean your hands and work surface. Hold the mirrors by their edges and use glass cleaner to clean their surfaces.

2. Place a 1 strip of double-sided adhesive tape on the back of a mirror and insert the mirror, shiny side up, inside the box lid.

3. Place double-sided tape along the lower half of the back of a second mirror and stick it against one of the inner sides of the lid.

4. Stick the third mirror adjacent to the second one so that all 3 mirrors merge to form a corner inside the lid.

5. Look inside the reflective corner of the cube. With one eye closed, your open eye will be directly centered at the apex of the corner. It will stay there even when you move the cube at various angles.

Applications:

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