Download Chapter 14 Section 2

Chapter 14 Section 2
Lens: a transparent material with at least one curved surface that causes
light rays to bend, or refract, as they pass through.
The image that a lens forms depends on the shape of the lens
Convex lens: thicker in the middle than at the edges
Optical axis: perpendicular to the surface at its thickest point
Rays are refracted toward the center of the lens to pass
through a single point—the focal point
Focal length—depends on the shape of the lens
Forming images with a convex lens:
Depends on where the object is relative to the focal point of the lens
If object is outside the focal length from the lens, the image is real, smaller
and upside down and on the opposite side of the lens from the object
If object is between 1 and 2 focal lengths from the lens, the image is real,
enlarged and upside down and on opposite side of the lens
If object is less than one focal length from the lens, its image is virtual,
enlarged and upright and on the SAME side as the lens
Concave lenses: is thinner in the middle and thicker at the edges
Light rays pass through and bend outward away from the optical axis
The image is virtual, upright and smaller than the object
Lenses and Eyesight
Cornea: the transparent covering on your eyeball where light enters the eye
Pupil: after passing through the cornea, rays pass behind the pupil to a
flexible convex lens
Light rays pass through it, and bend and form an inverted image on your
retina
Retina: inner lining of your eye, cells convert light images into electrical
signals sent to the brain
To see clearly, an image must be focused exactly on your retina
The retina is always a fixed distance from the lens
For an image to be formed on the retina, focal length has to change as the
distance of the object changes. Muscles attached to the lens in your eye
allow for this
Farsightedness: can see distant objects clearly, but can’t see close up
(eyeball is too short or the lens isn’t curved enough to form an image of
close objects on the retina—Need convex lenses to correct this
Astigmatism: occurs when the surface of the cornea is curved unevenly—
corneas are more oval than round in shape, also causes blurry vision at all
distances
Nearsightedness: can see clearly only when objects are nearby (eyeballs
may be too long or their lenses cannot be made flat enough to form an image
on the retina of an object far away—need concave lenses to correct this)
Section 3: Optical Instruments:
Telescopes: uses a lens or a concave mirror to gather light from distant
objects—as a result, distant objects appear much brighter
Refracting telescope: uses two convex lenses to gather and focus light from
distant objects/
You see an enlarged, inverted, virtual image of the real image formed
by the objective lens
Reflecting telescope: uses a concave mirror, a plane mirror, and a convex
lens to collect and focus light from distant objects.
Telescopes in Space: Hubble website—and info in book—pg. 470
Microscope: uses two convex lenses with relatively short focal lengths to
magnify small, close objects
Has an objective lens and an eyepiece lens
Cameras: wide-angle lenses and telephoto lenses