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Sci 8- Unit 3: Topics 4-5
Transcript of Sci 8- Unit 3: Topics 4-5
Light & Optical
Seeing round corners
Illuminating Egyptian tombs
Topic 4 -
Start on page 208
A lens is a curved piece of transparent material (glass/plastic).
When light rays pass through it, the light is refracted, causing the rays to bend.
A double concave lens =
Light passing through the thicker more curved areas of the lens will bend more than the thinner areas, causing the light to spread out or diverge.
A double convex lens
is thicker in the middle, this causes the light to come together at a focal point, or converge.
Lenses are useful optical devices.
Eyeglasses, have been made from lenses since the thirteenth century.
A convex lens refracts the light rays from an object so they can be focused.
The lens in the human eye is a convex lens, which focuses the light rays entering your eye to a point on your retina (a light sensitive area at the back of the eye). The image you see is formed on the retina.
How light works in your eye
What do all the parts do?
please Read p. 210
Lenses and Mirrors
Watch an Eye dissection?
cool photo gallery
Putting It in Focus
In a camera, if an object moves closer to the film, the lens must move away to keep the image in focus.
In the human eye, the lens cannot move, so the ciliary muscles change the shape of the lens
(by making the lens bulge in the middle if the image comes closer to you and stretch if the object is further away)
As people become older, the lens stiffens and loses its' ability to change shape (doesn't bulge) and many people need to wear (convex lens) reading glasses, so that the images can be focused.
The natural adjustment in the size of the pupils is called the iris reflex, which is extremely fast.
This iris reflex action automatically adjusts the pupil when you go from a darkened area to a well lit area, or, from a well lit area to a darkened one.
(You can test this with a flashlight-easily)
Read pages 216 and 217
Define 'Blind Spot' and 'Optic Nerve' in your notes
on page 217, follow the instructions on figure 3.37 to find your blind spot!
TOPIC 4 Review-
Questions 2,3,4 & 6
read #6 carefully!
Topic 5 -
on Page 221
Tools have been developed, to extend our vision, enabling us to see tiny micro-organisms, far-off distances and the vast reaches of outer space.
refracting vs. reflecting
please read pages 221-222
to compare the two types
of telescopes below....
the sense of sight 2mins
detailed video on the eye 2mins
44 seconds on ciliary muscles
notice the shape of the lens in the eye!
This was the first design
It uses two lenses to gather and focus starlight
early astronomers to use this telescope?
use mirrors instead of lenses to gather and focus the light from the stars.
biggest telescope on earth?
These can be built bigger, so they can see into space further
KECK telescope in Hawaii
Binoculars are actually two reflecting telescopes mounted side by side.
In binoculars, the telescopes are shortened by placing prisms inside, which serve as plane mirrors.
In this way, the light entering the binoculars can be reflected back and forth inside a short tube.
yes, we can't forget about the close association to
Usually more than one objective and eyepiece lens are used to increase the magnification and improve the sharpness of the image.
out of the atmosphere
Uses of plane mirrors
TOPIC 4-5 WRAP UP-
Topics 4 & 5