Reflector

If you’ve thought what I was doing two days before IIT-JEE (If you don’t know IIT-JEE is the entrance exam to the most prestigious engineering institutions in India, IIT). Here’s it:

Date: 8/4/2010

Work: It reflects the light, incident on it, to the direction from which it came. I think it is used in the glow in the dark signboards on the road.

Working: It uses three mutually perpendicular reflecting surfaces.

I assume my axes to be along the lines of intersection of the planes of the reflecting surfaces. If (α, β, γ) are the direction ratios of the initial ray. After reflecting from the mirror parallel to the x-y plane the direction ratios will become (α, β, -γ). After the other two reflections it will be (-α, -β, -γ) i.e. opposite the original ray.

Making: First, I took a cardboard sheet. And cut squares (2 cm × 2 cm) from it. Then I made a half-thick cut along a diagonal, and then folded along it.

Now I made the outer side reflecting. For this I used Aluminium foil. Now I made two more of these and joined them like this.

I joined surfaces 1 & 5, 1 & 3 and finally 3 & 5 such that 1, 3 & 5 formed three surfaces of a tetrahedron (something like the edge of a cube). The reflecting surface is the inner surface of the tetrahedron. Then I used nine more squares to make something which looked like:

It worked well but I think there are better reflecting materials than Aluminium foil.

Things used

1. Scissors
2. Blade
3. Tape
4. Glue
5. Cardboard
6. Aluminium Foil

Here are some photos of the one I made:

And it works, Can you spot it?