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 are brought 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.
FOCAL POINT Convex lens F Focal Point (Principal Focus). 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 OF A CONCAVE LENS Parallel rays Principal axis. 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.
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 Length
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 Focal Plane
Constructing Images Through Ray Diagrams
Three Rules of Refraction for 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 Refraction for 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.
Diverging Lenses Ray Diagrams 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.
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)
Object Image Relationship Case 1: The object is located beyond 2F: image will be an inverted image the image is reduced in size
Object Image Relationship Case 2: The object is located at 2F: the image will be inverted the image dimensions are equal to the object dimensions
Object Image Relationship Case 3: The object is located between 2F and F: the image will be located beyond the 2F point the image will be inverted the image is larger in size
Object Image Relationship Case 4: The object is located at F: no image is formed
Object Image Relationship Case 5: The object is located in front of F: somewhere on the same side of the lens as the object an upright image the image is enlarged
Object Image Relationship Converging Lens Summary
Object Image Relationship Diverging Lens Summary