Optics Concepts for Standard Physics, Installment 1 (as of 4 September)

• Light rays travel in straight lines in our room.
• Light rays diverge from a spherical (sort of ) source such as a light bulb.  If the source is very far away, the rays are essentially parallel.
• Non-parallel rays may diverge or converge.
• In optics, angles are usually measured from the normal, or a perpendicular line at the place the rays meet the surface you're interested in.
• The law of reflection is always true.
• Loosely speaking, there are two kinds of reflection: regular and diffuse.
• Only a mirror of half your height is necessary to see your whole body. This can be proven by drawing a ray diagram.
• To a large extent, the characteristics of an image are determined by our brain's interpretation of the light it detects.
• Our brains interpret all rays as traveling in straight lines directly to our eyes, hence we get two kinds of image: real and virtual.
• Light travels at a finite, constant speed.
• Light rays travel at different constant speeds in different materials.
• Light follows the path of least time in going from one point to another. If two light rays follow different paths in going from one point to another, the travel time must be equivalent.
• Light rays refract when they strike an interface b/w two materials at an angle. They do this b/c one part of the ray speeds up or slows down first.
• For a semicircular mirror, the focus is half the radius, whether virtual or real.
• When light strikes the surface of a transparent object, part of it is reflected, and part is transmitted.
• Parabolic reflectors are used as antennae b/c they do a good job of reflecting incident rays to the focus.
• When light passes from a "slow" material to a "fast" one, total internal reflection can occur. Total internal reflection occurs at some critical angle to the normal and beyond. In total internal reflection there is no refraction.
• The index of refraction of a material is inversely proportional to the speed of light in the material. The higher the index, the slower light moves in the material.
• Snell's law can be used to predict angles of refraction.

Back to Standard Physics Main Page