Chapter 20 Mirrors and Lenses

Objectives 20.1 Explain how an image is formed in three types of mirrors 20.1 Identify examples and uses of plane, concave, and convex mirrors.

Objectives 20.2 Describe the types of images formed with convex and concave lenses 20.2 Cite examples of how these lenses are used 20.2 Explain how lenses are used to correct vision

Objectives 20.3 Compare refracting and reflecting telescopes 20.3 Explain how a camera creates an image 20.4 Describe the development and repair of the Hubble Space Telescope 20.4 Discuss the goals and uses of the Hubble Space Telescope

Objectives 20.5 Explain how a laser produces coherent light and how it differs from incoherent light 20.5 Describe polarized light and the uses of polarizing filters 20.5 Apply the concept of total internal reflection to the uses of optical fibers

What is a Mirror? Mirrors are coated with Silver or Aluminum Silver is better (99 – 92), not every color equal Two reflections, one from glass, one from back Silver reflects 99 RG and 97 B Aluminum 92 RG and 90 B

Flat Plane Mirror Image reversed Left- Right Image formed equal distance behind mirror Image is Virtual – Rays don’t converge Image is Upright

Can you see more of yourself by standing farther away? Predict: Does standing farther away allow you to see more of yourself? Try it: Use a flat plane mirror provided, and determine if standing farther away allows you to see more of yourself Question: How big of a mirror do you need to see your whole image?

Left-Right Reversal Verify by looking into the mirror that you are flipped left and right. How does this change your perception of what you really look like?! See your real-self using two mirrors

Left Hand in front of mirror Your twin raised their right hand

See your REAL self by using two mirrors

Real or Virtual Image? Plane mirror produces a virtual image because light only appears to be behind mirror. – The mirror is opaque A real image actually has light rays where the image is – I am a real image, there really is light bouncing off me – The person in the mirror, really no light where the image is

Light only appears to come from location

Concave Mirrors Curved in, Focus Light Focal point is where distance rays converge

Convex Mirrors Curved out, Diverge Light Focal point is where image would seem to be

Convex Mirror Image formed is very small (usually) compared to real object, so it appears farther away – Warning signs on mirrors

Terminology Focal Point: Place where parallel rays from a distance converge together Focal Length: Distance from mirror to focal point

Image Formed at Intersection

More on Eye

Concave Mirror/Convex Lens Practice Sheet

Telescopes Refracting Telescope: Uses 2 Convex Lenses to gather and focus light from distance objects

Telescopes – More than you need to know Refracting Telescopes Issues – Objectives lens needs to be large to form a bright image – Their own weight causes them to sag and distort the image Image formation of Refracting – We see a large, inverted, virtual image of real image

Telescopes Reflecting Telescope: Uses a concave mirror, plane mirror, and a convex lens to focus light – Actually see a real, upright image

Telescopes More than you need to know – Easier to make the reflecting (less costly, less issues)

Microscopes Are really Refracting Telescopes, but look at objects that are close by

Cameras Use a lens to focus light onto the film

Moving the Convex Lens

One Focus

Total Internal Reflection When all light reflects due to a large angle (critical angle) – Looking into distance water = large angle = critical angle = total reflection

Total Internal Reflection Optic Fibers use this principal

Lasers Create Coherent Light by Stimulated Emission An electron in an excited state hit by a photon will fall releasing light in phase with the light that hit it Very Inefficient ( < 1%)

Which is coherent?

Simulator