While you are
watching the video
think about why this
is happening.
https://www.youtube.com/watch?v=eeLwLNvOUCs
Mirrors &
Lenses
Notes
Light Rays & the Path of Light
• If you could trace the path of one light wave when
it leaves its source you would find that light travels
in straight lines.
• Use an arrow called a ray to show the path and
direction of a light wave.
Rays & Reflected and Refracted Light
• Rays help to show the path
of light even after it
bounces or bends.
• Light waves that bounce off
objects are reflected.
• Light waves that bend
when passing from one
medium to another are
refracted.
• Rays in ray diagrams can
show changes in the
direction of light due to
reflection & refraction.
Ray Diagram Vocabulary
• Optical (Principle) axis – A straight line drawn
outward from the center of the mirror or lens.
• Focal point – The point at which rays meet after
reflection or refraction.
• Focal length – The distance between the surface of
the mirror or lens and the focal point.
Mirrors & Reflection of Light
• The shape of a mirror affects the way light reflects
from it.
• Mirrors are classified by shape. There are 3
different shapes of mirrors:
• Plane
• Concave
• Convex
Plane Mirrors
• A plane mirror is a mirror that has a flat surface.
• In a plane mirror the image is right-side up and
the same size as the object.
• Images in plane mirrors are reversed from left to
right.
• In a plane mirror the image appears to be the
same distance behind the mirror as the object is in
front of the mirror.
• So the image formed is a virtual image.
– A virtual image is an image through which the light
does not travel.
Concave Mirrors
• A concave mirror is a mirror that is curved inward
like the inside of a spoon.
• If the object is more than 1 focal length away from
the mirror, the image is up-side down and smaller
in size than the object.
• If the object is more than 1 focal length away from
the mirror, the image appears to be in front of the
mirror.
• So the image formed is a real image.
– A real image is an image through which the light
passes.
Concave Mirrors
• If the object is less than 1 focal length away from
the mirror, the image is right side up and larger in
size than the object.
• If the object is less than 1 focal length away from
the mirror, the image appears to be behind the
mirror.
• So the image formed is a virtual image.
Convex Mirrors
• A convex mirror is a mirror that is curved outward
like the back of a spoon.
• In a convex mirror the image is right-side up and
smaller in size than the object.
• In a convex mirror the image appears to be behind
the mirror.
• So the image formed is a virtual image.
Why is the girl’s reflection in the spoons different?
Which picture shows the back of the spoon?
Lenses & Refraction of Light
• A lens is a transparent object that forms an image
by refracting light.
• The shape of a lens affects the way light refracts
from it.
• Lens are classified by shape.
• There are 2 different shapes of lenses:
– Concave – This lens causes rays to converge
(come together)
– Convex – This lens causes rays to diverge
(spread apart)
Convex Lenses
• A convex lens is a lens that is thicker in the middle
than at the edges.
• If the object is less than 1 focal length away from
the lens, the image will be a right-side up, larger,
virtual image.
• If the object is more than 2 focal lengths away
from the lens, the image will be a up-side down,
smaller, real image.
• Convex lenses are used in magnifying glasses,
cameras, and sometimes eyeglasses.
Concave Lenses
• A concave lens is a lens that is thinner in the
middle than at the edges.
• Concave lenses form images that are right-side up
and smaller than the original object.
• Because the rays diverge and never touch the
images are all virtual images.
• Concave lenses are used in telescopes,
microscopes, and eyeglasses.