University Physics Volume 3

# Key Terms

### Key Terms

aberration
distortion in an image caused by departures from the small-angle approximation
accommodation
use of the ciliary muscles to adjust the shape of the eye lens for focusing on near or far objects
angular magnification
ratio of the angle subtended by an object observed with a magnifier to that observed by the naked eye
apparent depth
depth at which an object is perceived to be located with respect to an interface between two media
Cassegrain design
arrangement of an objective and eyepiece such that the light-gathering concave mirror has a hole in the middle, and light then is incident on an eyepiece lens
charge-coupled device (CCD)
semiconductor chip that converts a light image into tiny pixels that can be converted into electronic signals of color and intensity
coma
similar to spherical aberration, but arises when the incoming rays are not parallel to the optical axis
compound microscope
microscope constructed from two convex lenses, the first serving as the eyepiece and the second serving as the objective lens
concave mirror
spherical mirror with its reflecting surface on the inner side of the sphere; the mirror forms a “cave”
converging (or convex) lens
lens in which light rays that enter it parallel converge into a single point on the opposite side
convex mirror
spherical mirror with its reflecting surface on the outer side of the sphere
curved mirror
mirror formed by a curved surface, such as spherical, elliptical, or parabolic
diverging (or concave) lens
lens that causes light rays to bend away from its optical axis
eyepiece
lens or combination of lenses in an optical instrument nearest to the eye of the observer
far point
furthest point an eye can see in focus
farsightedness (or hyperopia)
visual defect in which near objects appear blurred because their images are focused behind the retina rather than on the retina; a farsighted person can see far objects clearly but near objects appear blurred
first focus or object focus
object located at this point will result in an image created at infinity on the opposite side of a spherical interface between two media
focal length
distance along the optical axis from the focal point to the optical element that focuses the light rays
focal plane
plane that contains the focal point and is perpendicular to the optical axis
focal point
for a converging lens or mirror, the point at which converging light rays cross; for a diverging lens or mirror, the point from which diverging light rays appear to originate
image distance
distance of the image from the central axis of the optical element that produces the image
linear magnification
ratio of image height to object height
magnification
ratio of image size to object size
near point
closest point an eye can see in focus
nearsightedness (or myopia)
visual defect in which far objects appear blurred because their images are focused in front of the retina rather than on the retina; a nearsighted person can see near objects clearly but far objects appear blurred
net magnification
($MnetMnet$) of the compound microscope is the product of the linear magnification of the objective and the angular magnification of the eyepiece
Newtonian design
arrangement of an objective and eyepiece such that the focused light from the concave mirror was reflected to one side of the tube into an eyepiece
object distance
distance of the object from the central axis of the optical element that produces its image
objective
lens nearest to the object being examined.
optical axis
optical power
(P) inverse of the focal length of a lens, with the focal length expressed in meters. The optical power P of a lens is expressed in units of diopters D; that is, $1D=1/m=1m−11D=1/m=1m−1$
plane mirror
plane (flat) reflecting surface
ray tracing
technique that uses geometric constructions to find and characterize the image formed by an optical system
real image
image that can be projected onto a screen because the rays physically go through the image
second focus or image focus
for a converging interface, the point where a bundle of parallel rays refracting at a spherical interface; for a diverging interface, the point at which the backward continuation of the refracted rays will converge between two media will focus
simple magnifier (or magnifying glass)
converging lens that produces a virtual image of an object that is within the focal length of the lens
small-angle approximation
approximation that is valid when the size of a spherical mirror is significantly smaller than the mirror’s radius; in this approximation, spherical aberration is negligible and the mirror has a well-defined focal point
spherical aberration
distortion in the image formed by a spherical mirror when rays are not all focused at the same point
thin-lens approximation
assumption that the lens is very thin compared to the first image distance
vertex
point where the mirror’s surface intersects with the optical axis
virtual image
image that cannot be projected on a screen because the rays do not physically go through the image, they only appear to originate from the image

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