virtual focal point concave thin lens diverging lens
TRANSCRIPT
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Virtual Focal Point
Concave Thin Lens
Diverging Lens
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Concave Thin Lens
Virtual Image
o
i
o
id
d
h
h io d
1d1
f1
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No matter where the object is: Image is always virtual, smaller and upright
FF
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The Human Eye
Web Links: Eye lens,
Vision and Eyesight
Near Point – Closest distance the eye
can focus on (about 25 cm when we are
young)
Far Point – Farthest distance the eye can focus on (should be )
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Someone who is Nearsighted cannot focus on far away objects. (Their far
point is not at infinity.)
Nearsightedness can be corrected with diverging lenses
Here’s how it works
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Ex:
Without my contact lenses, I need to stand 35 cm or less from the TV in order to see it in focus. Find the focal length of the contact lenses that correct my
vision.
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Someone who is Farsighted cannot focus on objects too near.
Farsightedness can be corrected with converging lenses
Here’s how it works
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The man has a near point of 48 cm. His reading glasses are 2.0 cm from his eyes, and with them on, he can read the newspaper as
close as 25 cm to his eyes. Find the focal length of his glasses
Ex:
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Lens Aberrations
1) Spherical Aberration
Can you think of two ways that this problem could be eliminated?
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2) Chromatic Aberration
How to correct this problem?
Compound (Achromatic)
Lens
Do mirrors ever experience Chromatic Aberration?A. Yes B. No
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Two people who wear glasses are camping. One is nearsighted, and the other is farsighted.
Whose glasses would be useful in starting a fire by focusing the sun’s rays?
A. The nearsighted person
B. The farsighted person
C. Any piece of glass will do the trick
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Try these problems A convex lens has a focal length of 5cm. An object is placed 7 cm from the lens. Determine the image distance and the image size. A convex lens has a focal length of 10cm. An object is placed 7 cm from the lens. Determine the image distance and the image size. A concave lens has a focal length of 8cm. An object is placed 12 cm from the lens. Determine the image distance and the image size. A concave lens has a focal length of 12cm. An object is placed 23 cm from the lens. Determine the image distance and the image size.
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lens
book
13cm
If the image of the book is 5.0 cm below the lens, find the focal length of the lens.
Challenge problem…Hint di = -(f-5) cmSolve a quadratic to find f…
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Sign conventions for Lenses
Focal length (f)
+ converging
- diverging
Object distance (do)
+ object on the left
Image distance (di)
+ image on the right (real)
- image on the left (virtual)
Magnification (m)
+ upright
- inverted