Optics -- How We See Space

What are “Optics?”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 LightOur 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 reflected off its surface.

It can be REFLECTED• Light bounces back at the same angle it hits a surface.

When Light Hits a Surface…

When Light Hits a 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)

When Light Hits a Surface…

When Light Hits a Surface…

Let’s Start by Studying ReflectionLet’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 reflection relative to the normal.

The Law of ReflectionThe 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 SMOOTH surface.

DIFFUSE reflection happens when lighthits and bouncesback off a ROUGH surface.

Now Let’s Look at MirrorsNow Let’s Look at Mirrors

1.Plane mirrors = straight/flat mirrors

2.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 MirrorsPlane or Straight Mirrors

1.Angle of incidence = angle of reflection.

2.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.

3.The image appears to be the same distance behind the mirror as the object is in front of the mirror.

“Spherical” (Curved) Mirrors“Spherical” (Curved) Mirrors

1.For both curved mirrors, the angle of incidence equals the angle of reflection.

2.A convex mirror will always produce a virtual image of an ordinary object.

3.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? 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?”What is “Refraction?”

• Refraction: Light refracts (bends) when it crosses a boundary between two different media(air to water ;

air to glass)

Law of RefractionLaw 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?”What is “Refraction?”

• Light slows down when it enters a more dense medium.

• Light speeds up when it enters a less dense medium.

The index of refraction tells us how much light slows down in different materials.

Dense materials have a high index of refraction & cause light to bend more. (glass, diamonds)

The Index of Refraction:The Index of Refraction:

• Light bends towards the normal in dense material (glass, water, diamond)• Light bends away from the normal in less dense material (air)

Remember that 90 degrees “Normal” Reference Line!

Remember that 90 degrees “Normal” Reference Line!

Take a Look at LensesTake 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)