Download Refraction Rules for a Diverging Lens

Physics 100
Notes – Lenses
What is a lens?
A lens is merely a carefully ground or molded piece of transparent material that refracts light rays in such a
way as to form an image.
Converging or Convex Lenses
Incident rays which travel parallel to the principal axis will refract through the lens and converge to a point
called the focal point.
Diverging or Concave Lenses
Incident rays traveling parallel to the principal axis will refract through the lens and diverge, never intersecting .
VOCAB
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Optical center-center of the lens
Principal axis-horizontal line that passes through the optical center.
Focal point- point in which all parallel rays of light will converge
Focal length – the distance from optical center of lens to the focal point
do= object distance from optical center
di = image distance from optical center
ho = size of object
hi= size of image
Power of lens
P= 1/do + 1/di
Magnification of lens M= hi/ho
An image location is a location in space where all the refracted light appears to come from.
REAL Images
 Can be projected onto a screen, slide projector, camera
 Are formed when rays of light converge
 Are inverted (upside down)
VIRTUAL Images
 Can NOT be projected onto a screen
 Are formed when rays of light diverge
 Are upright
Refraction Rules for a Converging 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 that passes through the center of the lens will in affect continue in the same direction
that it had when it entered the lens.
Refraction Rules for a Diverging Lens

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 that passes through the center of the lens will in affect continue in the same direction
that it had when it entered the lens.
The Lens Equations
eye
Lens Equation Conventions
do = positive for real objects
POSITIVE for virtual objects
h = negative for inverted images
positive for upright images
di = positive for real images
Negative for virtual images
f = positive for convex lenses
Negative for concave lenses
Problems
A 4.00-cm tall light bulb is placed a distance of 45.7 cm from a double convex lens having a focal length of
15.2 cm. Determine the image distance and the image size.
A 4.00-cm tall light bulb is placed a distance of 8.30 cm from a double convex lens having a focal length of
15.2 cm. Determine the image distance and the image size.
A 4.00-cm tall light bulb is placed a distance of 35.5 cm from a diverging lens having a focal length of -12.2
cm. Determine the image distance and the image size.