lenses chapter 30 - pbworks
TRANSCRIPT
Chapter 30: Lenses
Types of Lenses
Piece of glass or
transparent material
that bends parallel
rays of light so they
cross and form an
image
• Two types:
– Converging
– Diverging
Converging Lenses
Parallel rays arebrought to a focus by a converging lens (one that is thicker in the center than it is at the edge).
Diverging Lenses
A diverging lens (thicker at the edge than in the center) make parallel light diverge; the focal point is that point where the diverging rays would converge if projected back.
CENTERS OF CURVATURE, PRINCIPAL AXIS,
OPTIC CENTER.
The centers of the two spheres of which the
spherical surfaces of the lens form parts are called
CENTERS OF CURVATURE.
CENTERS OF CURVATURE, PRINCIPAL AXIS,
OPTIC CENTER.
The straight line joining the centers of curvature of
a lens is called its PRINCIPAL AXIS.
CENTERS OF CURVATURE, PRINCIPAL AXIS,
OPTIC CENTER.
The point inside the lens through which a ray of light
passes without any deviation is known as its OPTIC
CENTER.
F – Focal Point (Principal Focus).
Convex lens
Rays parallel to the principal axis of a convex lens, after
refraction through the lens, get converged to a fixed point
on the principal axis of the lens. This point is called the
Focal Point of the lens.
FOCAL POINT
FOCAL POINT OF A CONCAVE LENS
Principal axis.
Parallel rays
F – Focal Point
Rays parallel to the principal axis of a concave lens,
after refraction appear to diverge from a fixed point
on the principal axis. This point is called the FOCAL
POINT of the lens.
Focal Length
The focal point F
and focal length f
of a positive
(convex) lens,
a negative
(concave) lens,
a concave mirror,
and a convex
mirror.
Focal Plane
Incident parallel
beams, that are
not parallel to
the principal
axis, focus at
points above or
below the focal
point, making up
the focal plane
Constructing Images
Through Ray Diagrams
Three Rules of Refractionfor a double convex lens
• Any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens.
• Any incident ray traveling through the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.
• An incident ray which passes through the center of the lens will in effect continue in the same direction that it had when it entered the lens.
Three Rules of Refractionfor a double convex lens
Diverging Lenses –Ray Diagrams
• Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the lens and travel in line with the focal point (i.e., in a direction such that its extension will pass through the focal point).
• Any incident ray traveling towards the focal point on the way to the lens will refract through the lens and travel parallel to the principal axis.
• An incident ray which passes through the center of the lens will in affect continue in the same direction that it had when it entered the lens.
Diverging Lenses – Ray Diagrams
• 1. Pick a point on the top of the object
and draw three incident rays traveling
towards the lens.
• 2. Once these incident rays strike the
lens, refract them according to the three
rules of refraction for double concave
lenses.
Diverging Lenses – Ray Diagrams
3. Locate and mark the image of the top of
the object.
Diverging Lenses – Ray Diagrams
Object – Image Relationship
Converging Lens
• Case 1: the object is located beyond the 2F point
• Case 2: the object is located at the 2F point
• Case 3: the object is located between the 2F point and the focal point (F)
• Case 4: the object is located at the focal point (F)
• Case 5: the object is located in front of the focal point (F)
• image will be
an inverted image
• the image is
reduced in size
Object – Image Relationship
Case 1: The object is located beyond 2F:
• the image will be
inverted
• the image
dimensions are
equal to the object
dimensions
Object – Image Relationship
Case 2: The object is located at 2F:
• the image will
be located
beyond the 2F
point
• the image will
be inverted
• the image is
larger in size
Object – Image Relationship
Case 3: The object is located between 2F and F:
• no image is formed
Object – Image Relationship
Case 4: The object is located at F:
• somewhere on
the same side of
the lens as the
object
• an upright image
• the image is
enlarged
Object – Image Relationship
Case 5: The object is located in front of F:
Object – Image Relationship
Converging Lens Summary
Object – Image Relationship
Diverging Lens Summary