Transcript 07b. Ray Rules for Lenses0

SEEING
THROUGH A
LENS
 We see the world through lenses.
 Eye glasses = lenses. Contact lenses = lenses.
 Magnifying glasses = lenses. Microscopes = lenses. Camera =
lenses.
 What about individuals that do not need visual aids?
Yes, they still see the world through lenses in their eyes.
A lens!!
2 TYPES
 Convex (Converging) Lens
 Parallel light rays converge (come to a
single point) after refraction through
the lens.
 Concave (Diverging) Lens
 Parallel light rays diverge (move away
from each other) after refraction from
the lens.
NOTE
 These rules only apply to THIN lenses
 Refraction (Lateral displacement) would occur
otherwise.
ANOTHER VIEW
CONVEX LENS
 F = Primary Focus (2 x F = 2F)
 O = Optical Centre
 F’ = Secondary Focus (2 x F’ = 2F’); located on same
side as incident rays
CONVEX
CHARACTERISTIC RAYS
 Any incident ray passing through the Secondary
Focus will…
 REFRACT PARALLEL TO THE PRINCIPAL
AXIS
CONVEX
CHARACTERISTIC RAYS
 Any incident ray passing through the Optical Centre
will…
 PASS UNDEVIATED (STRAIGHT THROUGH)
CONVEX
CHARACTERISTIC RAYS
 An incident ray parallel to the principal axis will…
 REFRACT THROUGH THE PRIMARY FOCUS
CONVEX
CHARACTERISTIC RAYS
 Any incident ray passing through 2F’ will…
 REFRACT THROUGH 2F
PREDICTING IMAGES
IN A CONVEX LENS
 Object located beyond 2F’
 Where is the image?
 The object appears to come where the light originates from.
 The image is also located where all the rays come together.
LOST (LAST)
 Location: Between F & 2F
 Attitude/Orientation: Inverted
 Size: Smaller than object
 Type: Real (Different from Mirrors)
CONCAVE
CHARACTERISTIC RAYS
 Any incident ray parallel to the principal axis will…
 REFRACT AS IF IT HAD PASSED THROUGH
THE PRIMARY FOCUS
CONCAVE
CHARACTERISTIC RAYS
 Any incident ray moving toward the Secondary Focus
will…
 REFRACT PARALLEL TO THE PRINCIPAL
AXIS
CONCAVE
CHARACTERISTIC RAYS
 Any incident ray passing through the Optical Centre
will…
 PASS UNDEVIATED (GO STRAIGHT
THROUGH)
PREDICTING IMAGES
IN A CONCAVE LENS
 Object located beyond 2F
 Where is the image? All the refracted rays diverge!
 If the rays diverge, the image is where the refracted
rays appear to meet in the opposite direction!
LOST (LAST)
 Location: Same side as object
 Attitude (Orientation): Upright
 Size: Smaller than object
 Type: Virtual (Different from Mirrors)