Exercises
1
.
Fray is holding up several large pieces of curved pieces of glass in front of her.
Determine the type of lenses (converging/diverging) these are, and what kind of
Fray image (real/virtual) you are seeing through the glass.
This is Fray with no
lens in front of her.
(a)
(b)
(c)
2
.
Rank these lenses ((I)(IV)) from shortest to
longest focal point. Then rank these lenses from
greatest to least optical strength.
3
.
Kelly's eyeglasses have a focal length of +10cm and Fray's eyeglasses have a focal
length of 5cm. Whose eyeglasses could start a fire by focusing the light from the
Sun onto a piece of newspaper to ignite it—Fray’s or Kelly's?
4
.
Lens Practice: i) Locate the each of the following objects with a ray tracing, ii)
Locate each of the following objects with the thin lens equation, iii) Determine the
magnification with your ray tracing, iv) Determine the magnification
mathematically, v) Check that your answers match (if you didn’t already), vi)
Check your work with the applet on the course web page.
a)
An object is placed 4 cm from an
f
=+10cm lens.
b)
An object is placed 8 cm from an
f
=+10cm lens.
c)
An object is placed 8cm from an
f
=10cm lens.
d)
An object is placed 18 cm from an
f
=+10cm lens.
e)
An object is placed 18 cm from an
f
=10cm lens.
f)
An object is placed 15cm from a converging lens that has a focal length of
+7.5cm?
5
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 Spring '08
 MAHMUD

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