PHY ICS - The Institute of Physics in Ireland

light 41
How the eye works: introduction
Bulgaria
How the different parts of the eye and brain contribute to vision
You will need...
✔ an overhead projector
and screen
✔ small circles of red and
green filter (diameter
~ 2 cm)
✔ green and red filters
(106 and 139 from
suppliers of filters for
stage lighting)
✔ an image from the
Internet (www.
ebaumsworld.com/
manillus.html)
✔ for each person, a
square of black card
( ~ 4 × 4 cm), a pin, a
rubber band, two
matches and a long
measuring tape
✔ some plain white paper
✔ a thick black marker
pen
✔ an optician’s Snellan
chart
Background
The following experiments are
equally relevant to physics
students studying the
refraction of light by lenses
and to biology students
studying vision. They have
the enormous dual
advantages of involving
students actively in the
experiments yet requiring
only very simple equipment.
The nine experiments show
in turn how the following
parts of the visual system
contribute to human vision:
the aqueous humour, the
pupil, the lens, the retina, the
rods, the cones and the
brain.
The retina is the layer of
cells in the eye that are
sensitive to light, including
the rods (black-and-white
vision) and the cones (colour
vision). The fovea is the
place on the retina where the
cones are concentrated and
where the image is focused
for the best vision when you
look directly at something.
The brain also plays a vital
role in the amazing sense of
vision.
PHYSICS ON STAGE 3