1. Refraction & Lenses
Sections 11.7 and 11.8

2. Refraction
when light passes from one material (aka medium) to another, it bends because the speed of light travels at different speeds in different mediums
Ex. When light rays move from water into air, they speed up and bend away from the normal (that’s why a fish looks closer to the surface than it really is)

3. Light can undergo partial reflection and refraction at the same time at a surface.
Ex. Sunglasses, two way mirrors (buildings = less air conditioning)

4. Lenses
A lens is a curved, transparent device that causes light to refract as it passes through
Like mirrors, can be convex or concave
Many optical devices use more than one lens
Ex. A telescope has objective and eyepiece lenses)

5. Convex Lenses
A convex lens is thicker in the middle than at the outside edge (bulges outward)
Cause light rays to converge (come together) at a focal point

6. Convex Lenses
Usually used to make objects look larger, so long as you have the object close to the lens.
Example. magnifying glass, microscope, camera, human eye
Like concave mirrors, if the object is farther from the lens it will produce an inverted image that can either be larger or smaller depending on how far away it is.

7. Movement of Light through Convex Lenses
In a convex lens, an incoming ray parallel to the principal axis is refracted through the principal focus (F).

8. Focal Length
The greater the curvature of a lens, the more it bends light and hence the shorter the focal length.

9. Concave Lenses Cause light rays to diverge (spread apart)
A concave lens is thinner in the middle than at the outside edge (caved inward)
Cause light rays to diverge (spread apart)

10. Concave Lenses Always produce a smaller, upright image of the object
Used in some types of eyeglasses (for nearsightedness) and some telescopes, cameras

11. Movement of Light through Concave Lenses
In a concave lens, an incoming ray parallel to the principal axis is refracted so that it appears to come from the principal focus (F).

12. Summary of Lenses