Homework 7, Due by email to TA Nov 6
- (1 pt) What is the normal vector to the sphere {$x^2+y^2+z^2=1$} at the
surface point {$(x,y,z)$}?
- (1 pt) What is the normal vector to the paraboloid {$z=x^2+y^2$} at the
surface point {$(x,y,x^2+y^2)$}?
- (4pt, this question will take some thinking).
Imagine that you have an infinitely large room illuminated
by one infinitely long row of point lights. This figure
shows a side view of the room.
The lights are h above the floor and are 1
meter from each other. Assume that the ceiling above the
lights is black and that no light reflects off of anything.
An object at distance d from a light gets illuminated
with a brightness 1/d2 .
Each point on the floor is illuminated by all the lights,
but more brightly by the closer lights.
A point p directly below a light will be a little
brighter than a point q halfway between two such
points. That is the problem --- we want the floor (at least
the part directly below the line of lights) to be evenly
lit, at least within 20%.
However, the higher the line of lights, the more evenly the
floor will be lit.
Your question is to tell us what is the minimum value for
h so that the line of the floor below the line of
lights is evenly lit within 20%.
E.g., the brightness at p is {$$ \sum_{d=-\infty}^{\infty} \frac{1}{h^2+d^2} $$}