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SEEING SEEING THROUGH A THROUGH A
LENSLENS
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.
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
NOTE These rules only apply to THIN lenses
Refraction (Lateral displacement) would occur otherwise.
ANOTHER VIEW
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 PRINCIPAL 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)
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