Resource Lesson
Thin Lens Equation
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The thin lens equation is stated as follows:
where
d
_{o}
is the distance (measured along the axis) from the object to the center of the lens
d
_{i}
is the distance (measured along the axis) from the image to the center of the lens
f is the focal length of the lens
The expression 1/f in called the
power of a lens
. It is measured in Diopters, where 1 D = 1 m
^{-1}
.
When using this equation, signs are very important:
d
_{o}
positive
when the object is placed "in front of the lens"
d
_{i}
positive
when real images are formed (inverted, "behind the lens")
d
_{i}
negative
when virtual images are formed (upright, "in front of the lens")
f
positive
when the lens is
converging
f
negative
when the lens is
diverging
Remember that d
_{o}
, d
_{i}
, and f must be measured in the same unit - usually meters is preferred.
The following formula is used to calculate the magnification of an image:
If a problem states that a real image is formed that is twice as large as an object, then you would use the relationship d
_{i}
=
+
2d
_{o}
in the thin lens equation. If a problem states that a virtual image is formed that is twice as large as the object, then you would use the relationship that d
_{i}
=
−
2d
_{o}
.
Refer to the following information for the next three questions.
Suppose you are initially given a converging lens, made from crown glass, that has a focal length of +0.10 meter.
If this lens is to be used in air, which cross-sectional figure best represents its shape?
An object is placed 0.30 meter from the lens in the previous question. How far from the lens will the image of this object be formed?
Suppose this 0.800-meter tall object is now placed 0.20 meter in front of a second converging lens. If the distance of the image from the lens is 0.40 meter, then the height of the image is
Refer to the following information for the next four questions.
Suppose you are now given a double concave lens, also made from crown glass, that has a focal length of −0.10 meter.
Which cross-sectional figure best represents its shape?
This
diverging
lens can form only form ____ images.
An object is placed 0.20 meter from this diverging lens. How far from the lens will the image of the object be formed?
If the object in the previous question was 4.5 centimeters tall, how tall is its image?
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Snell's Law
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REV -
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Worksheet:
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APP -
Reflections
APP -
The Librarian
APP -
The Starlet
CP -
Lenses
CP -
Plane Mirror Reflections
CP -
Refraction of Light
CP -
Snell's Law
CP -
Snell's Law
NT -
Image Distances
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Laser Fishing
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Mirror Height
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Mirror Length
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Reflection
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Underwater Vision
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Basic Principles of Refraction
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Diverging Lens Vocabulary
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Lensmaker Equation
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Plane Mirror Reflections
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Refraction and Critical Angles
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Refraction Phenomena
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Refraction Through a Circular Disk
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Refraction Through a Glass Plate
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Refraction Through a Triangle
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Snell's Law Calculations
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Thin Lens Equation #2: Converging Lenses
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Thin Lens Equation #3: Both Types
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Thin Lens Equation #4: Both Types
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