15.2 Lenses
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Transcript of 15.2 Lenses
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15.2 Lensespp. 568 -579
Mr. Richter
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Agenda
Review HW Introduction to Lenses Notes:
Types of Lenses Converging Lenses
Distances and Images Diverging Lenses
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Objectives: We Will Be Able To… Determine whether an image produced by a lens is
real or virtual. Determine the orientation and magnification of an
image produced by a lens.
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Warm-Up:
Where do you see lenses used? What purpose do they serve?
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Types of Lenses
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Lenses
Curved objects change the direction of light.
Like mirrors, lenses form images, but by refraction instead of reflection.
Images may be real or virtual, depending on distance from the focal length (F).
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Types of Lenses
Converging Thicker in the middle than
it is at the rim.
Edges converge.
Diverging Thicker at the rim than it
is at the middle.
Edges diverge.
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Converging Lenses
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Converging Lens Image: Object at Infinity.
All rays of light converge on the focal point. Focuses light energy in one place. No image forms.
Good for burning holes and not much else.
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Converging Lens Image Object Closer than Infinity to the Focal Length
Image is real and inverted, and can be projected on to another surface.
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Converging Lens Image Object Closer than Infinity to the Focal Length
Image is smaller than object.
Seen in: Camera lens Human eye
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Corrective Vision: Farsightedness When the eye cannot move its focal point close
enough, nearby images are blurry. This hyperopia, or farsightedness, can be corrected by
a converging lens.
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Converging Lens Image Object Closer than Twice the Focal Length
At between twice the focal length and the focal length:
Image is magnified. Seen in:
movie or slide projector
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Converging Lens Image Object At the Focal Length
Rays of light never converge. Light is projected an infinite
distance way. No image forms.
Seen in light houses and search lights
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Converging Lens Image Object Closer than the Focal Length
Image is virtual. Image is projected larger
on the same side of the lens as the object.
Good for: magnifying glass binoculars
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Recap Images of Converging Lenses
Object Distance Real or Virtual MagnificationInfinity N/A: Point Image N/AGreater than focal length
Real and inverted. Image is smaller than object.
At focal length N/A: Image is projected to infinite distance.
N/A
Closer than focal length.
Virtual and upright.
Larger image the closer to the focal point.
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Diverging Lenses
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Diverging Lenses Diverging lenses only produce virtual
images. Used to produce upright images that
are smaller than the original but a wider viewing angle.
Like: viewfinders in (older) cameras.
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Corrective Vision: Nearsightedness When the eye’s focal point is too close, faraway
images are blurry. This myopia, or near sightedness, can be corrected by
a diverging lens.
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Wrap-Up: Did we meet our objectives?
Determine whether an image produced by a lens is real or virtual.
Determine the orientation and magnification of an image produced by a lens.
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Homework
p. 587-588 #15-18, 21