What are “Optics?” For this class we are going to define “optics” as the study of light and how it interacts with the mirrors and lenses that let us see into space.
Our Study Starts with Light Light basically moves in straight lines. An object “lights up” either because it is actually emitting light, or light is being reflectedoff its surface.
When Light Hitsa Surface… It can be REFLECTED Light bouncesbackat the same angle it hits a surface.
When Light Hitsa Surface… It can also be REFRACTED Light “bends” in response to entering a different medium(i.e. from air to water or from air to glass)
Let’s Start by Studying Reflection The Law of Reflection: When a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflectionrelative to the normal.
The Law of Reflection The normal is: always at a right angle to the surface being used.
SPECULAR reflection happens when lighthits and bouncesback off a SMOOTHsurface. DIFFUSE reflection happens when lighthits and bouncesback off a ROUGHsurface.
Now Let’s Look at Mirrors Plane mirrors = straight/flat mirrors Spherical Mirrors = curved/rounded mirrors (convex or concave) *** For ALL mirrors, the angle of incidence equals the angle of reflection (relative to a 90 “normal” line). .
Plane or Straight Mirrors Angle of incidence = angle of reflection. A plane mirror “fools you” by making your eyes and brain perceive a virtual image. The image is called “virtual” because it’s not really there. The image appears to be the same distance behind the mirror as the object is in front of the mirror.
“Spherical” (Curved) Mirrors For both curved mirrors, the angle of incidence equals the angle of reflection. A convex mirror will always produce a virtualimage of an ordinary object. A concave mirror can produce a virtual or a real image, depending on how close the object is to the mirror.
Virtual vs. Real Image? You have to look at a lens or mirror to see a virtual image You can see a real image without actually seeing the lens or mirror that created it.
What is “Refraction?” Refraction: Light refracts (bends) when it crosses a boundarybetween two differentmedia(air to water ; air to glass)
Law of Refraction The Law of Refraction (Snell’s Law): The degree to which light will bend depends on the indices of refraction of the media involved.
What is “Refraction?” Light slows downwhen it enters a more densemedium. Light speeds upwhen it enters a less dense medium.
The index of refraction tells us how much light slows downin different materials. Dense materials have a high index of refraction & cause light to bend more. (glass, diamonds) The Index of Refraction:
Light bends towards the normal in dense material (glass, water, diamond)
Light bends away fromthe normal in less dense material (air)
Remember that 90 degrees “Normal” Reference Line!
Take a Look at Lenses A lens is a specially-shaped piece of transparent material like glass or plastic used to bend light Convex = converging lens (light comes together) Concave = diverging lens (light spreads out)