Lenses can focus light and make
images in a very similar way to mirrors. Lenses
are either concave or convex. A convex lens will
focus light from a distant source to a point, the
focal point. Magnifying glasses are made with
convex lenses and can be used to start a fire.
The focusing is illustrated at the right.
Concave lenses spread light out
rather than bring rays together. The image from a
concave lens is therefore always virtual. The
focusing is illustrated to the right. To an
observer on the right side of the lens, the light
appears to come from the focal point on the left
side of the lens. The focal length of a concave
lens is assigned a negative number. Both concave
and convex lenses are used in a variety of
optical instruments, the subject of the next
lecture.
Lenses can focus light and make
images in a very similar way to mirrors. Lenses
are either concave or convex. A convex lens will
focus light from a distant source to a point, the
focal point. Magnifying glasses are made with
convex lenses and can be used to start a fire.
The focusing is illustrated at the right.
Concave lenses spread light out
rather than bring rays together. The image from a
concave lens is therefore always virtual. The
focusing is illustrated to the right. To an
observer on the right side of the lens, the light
appears to come from the focal point on the left
side of the lens. The focal length of a concave
lens is assigned a negative number. Both concave
and convex lenses are used in a variety of
optical instruments, the subject of the next
lecture.