Title: A light bulb never looked so lovely!
Topic: lenses and photometry
Background: Centuries before the courageous, isolated attempts by Vikings at trans-ocean exploration, the coastlines of Western Europe were alive with ships of all sizes and descriptions. Throughout the ages, safe navigation has remained a key concern of mariners.
Process: Go to the following web sites and use the information there to answer the following questions.
Questions:
1. Use the information at: http://www.groton.k12.ct.us/WWW/cb/turnon.html
and the links below to
create an original 300 word summary of lighthouses.
Mention: one ancient, one 17 Cth and one
modern lighthouse, their locations, construction
materials, sizes, sources of illumination, lens makers,
and types of lenses.
2. Lighthouses are generally located in what types of areas?
3. Go to: http://www.west.net/~pamass/htmfiles/freslens.htm
a) There are how many categories of fresnel lighthouse
lenses?
b) Which type is the most spectacular?
c) Why?
d) What are the purposes of a lighthouse lens?
e) Provide descriptions of its focusing power.
f) How does the lens increase the effective brightness
of the lamp?
g) The fresnel lens belongs to which of the two
general types of lenses?
4. a) Lighthouse lenses can be appreciated as striking, imaginative
glass sculptures. Please go to the
following URL's and collect
the indicated images.
i) http://members.aol.com/fairyfellr/lantern.html;
print: St. George Reef, view 1, Battery Point
and Cape
Blanco.
ii) http://nw3.nai.net/~cdd/lens.htm;
print: the lens from the Stonnington Lighthouse Museum
b) Arrange the images in increasing
order. Title each image.
5. If a lens gives a lamp an effective luminous intensity of 30 000
cd, at what distance would it give an
illumination of 4 000 lux?
6. Find the luminous intensity of a lamp - lens that gives an illumination
of 1 500 lux at a distance of 7 km.
7. Find the illumination from a 12 000 cd lamp - lens at a distance
of 10 km.
8. A ship located between two lighthouses receives equal illumination
from both. If it is 5.6 km from an
8 000 cd lighthouse to port (on its left) and the
lighthouse to starboard (on its right) is 8.2 km away,
find the luminous intensity of the starboard lighthouse.
9. A ship sailing between two lighthouses receives equal illumination
from both. If the port 7 500 cd
lighthouse it is 2.4 km away, what is the distance
to the starboard 6 000 cd lighthouse?
10. A ship sailing between two lighthouses receives equal illumination
from both. If the port 9 500 cd
lighthouse and the starboard 5 900 cd
lighthouses are located on headlands 2.7 km apart, where
is the ship?
11. A ship sailing between two lighthouses receives three times the
illumination from the port 4 800 cd
lighthouse 1.3 km away as it does from
the starboard 3 700 cd lighthouse. What is the distance to
the starboard lighthouse?
12. What is the future of lighthouses?