Transcript Lecture Slides - IRIS Science Academy

Week 8: Mirrors &
Lenses
November 6th, 2015
Katie Hellier
IRIS Science Academy
Last Week
• Light – what is it?
• Absorption – takes in photons
• Reflection – photons bounce off
• Refraction – photons pass through
material, but are bent
Video
• Concave and Convex Mirrors
• https://youtu.be/jtTBOMVMSYM
Reflection - Mirrors
• Light bouncing off mirror creates a virtual image
“behind” the mirror
• Virtual image – light rays
look like they come from a
point from behind the
mirror to the observer
(but there’s nothing
behind the mirror)
• Angles on each side of the
normal are equal – angle
formed on other side of
the mirror is the same
Curved Mirrors
• Mirrors can be curved, like in a funhouse
• Real light rays bend toward the center; imaginary move outward
• Changes how “far back” the image forms
• This creates a distorted shape, magnified or shrunken
• Magnification (m) is the scaling factor of the image
Real Images
• Real image is when
light rays converge to
one point (not
actually a material
thing)
• In a curved mirror, if
the object is far back
enough, an image
can be formed (on a
piece of paper, for
example)
• It’s also inverted!
Video
• How do Lenses Work
• https://youtu.be/qbPfzOuIeSM
Refraction - Lenses
• Lenses allow light to pass through, but bend it
(like glasses)
• Can create real and virtual images based on curvature
• Images can be larger, smaller, upright, inverted
Convex Lens
Concave Lens
Object is
inside focal
length
Object is
inside focal
length
Object is
outside
focal length
Object is
outside
focal length
Prism
• Prism – transparent optical device that refracts
light
• Two polished, flat sides must have an angle
between them
• The material used
changes how much
each wavelength is
bent  dispersion
Magnifiers
• Use convex lenses to create a magnified, virtual
image
• Level of magnification depends on location
between object and eye
• Can be used to concentrate light (eg magnifying
glass and the sun)
Microscopes and Telescopes
• Both create images of optics
• “Micro” – Greek word meaning small
• “Tele” – Greek word meaning far
• “Scope” – Greek word meaning to see
• Refracting microscopes & telescopes require 2 lenses to create
an image
• Reflecting telescopes use 1 lens and mirrors
• The largest telescope is 30m (~100ft) mirror in Mauna Kae, HI!
Video
• How telescopes work
• https://youtu.be/WvLspPgC1EU
Ray Diagrams
Rules for drawing a Ray Diagram:
1. Any ray that enters parallel to the axis on one side of the
lens proceeds towards the focal point F on the other side.
2. Any ray that arrives at the lens after passing through the
focal point on the front side, comes out parallel to the axis
on the other side.
3. Any ray that passes through the center of the lens will not
change its direction.
The Lens Equation
• Tells us where we can expect to find the image/object
• f – focal point: distance from the lens to its focus
• o – object: distance from lens to the object
• i – image: distance from lens to the image
• Don’t forget to pick one side of lens as positive, the other as
negative distance!
Object
Image
Lab – Building an Optical Device
• Solar Ovens - use your understanding of
reflection, absorption, lenses and mirrors to
make a solar oven.
• Telescopes – use your understanding of lenses
and the lens equation to make a refracting
telescope.