# Terminology ### Instructor’s Note

This Unit is very heavy on vocabulary, there is a set on flashcards on Quizlet to help you.

• An is a lens or mirror.
• An is the apparent reproduction of an object, formed by an optical element (or collection of them) reflecting and/or refracting light.
• Images can either be (same orientation as object) or (upside-down with respect to object).
• The optical axis is a line that passes through the optical element perpendicular to it
• The point where the optical axis meets the optical element is called the .
• The of a lens is where the lens is thickest (for a converging lens) or thinnest (for a diverging lens).
• The of a mirror is the center of curvature.
• Image and object distances are measured along the optical axis.
• Signs are relative to the path of the light.
• If the object is on the same side as the incoming light, then , otherwise .
• If the image is on the same side as the outgoing light, then , otherwise .
• For a lens, the incoming and outgoing sides are different (light goes through a lens).
• For a mirror, the incoming and outgoing sides are the same (light bounces off a mirror).
• Focal lengths are also signed. If the element tends to incoming parallel light (a or a ), then the focal length is negative. If the element incoming parallel light ( or ), the focal length is positive.

# Principles for Unit II

##### How light interacts with surfaces and materials
• Law of reflection which is best understood in the particle picture.
• Law of refraction which is best understood in the wave picture.
• Light slows when it enters a medium, but the energy of a photon cannot change. So the wavelength must!
##### Optical elements and ray diagrams
• The position of the image formed by an optical system is located at where:
• is the object distance, using the sign conventions used above.
• is the image distance, using the sign conventions used above.
• is the focal length with its correct sign.
• For ray diagrams: one ray in parallel and out through focal point, one ray in through focal point and out parallel, one ray using the center of the system.
• And point where photons seem to emerge can be used as an object. Such a point could be a real source of photons (an object) or an image from another optical element. 