Total internal reflection n 1 n 2 increase

Total internal reflection n 1 > n 2 increase n 1 until the refracted angle=90

Critical Angle the incident angle is called the critical angle

Example

Total Internal Reflection (Example) Can light passing from crown glass into air be totally internally reflected? If so, what is the critical angle? YES!!! since n 1>n 2 n 1=1. 52 n 2=1 Crown Glass Air

Poll If light from air is incident on glass, 1. it can not refract at the critical angle. 2. it may refract at the critical angle and not be transmitted through the glass.

Dispersion The index of refraction n depends on the frequency (i. e. color) of the light. As a result, different colors bend different amounts as they pass through glass or water, for example. If white light is incident on glass or water, then the different frequencies bend different amounts and the white light separates into its component colors. this effect is called dispersion.

Poll Which will have a greater angle of refraction, red or violet light? 1. red 2. violet 3. neither, they bend the same amount

Image formation by lenses Types of lenses

Lensmaker’s Equation (for a thin lens)

Converging Lens All rays parallel to the optic axis pass through the focal point F. Example: Double Convex (biconvex) F Note: nlens > noutside

All rays from an object intersect at the image What happens if you cover the top half the lens with a screen? 1. You’ll only see the top half of the image. 2. You’ll only see the bottom half of the image. 3. You’ll still see the image, but it will be only half as bright.

Three Easiest Rays To Sketch F Object Image F 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays through F emerge parallel to principal axis. Image is: real, inverted and enlarged (in this case).

3 Cases (converging lens) so>2 f Image Object so between f & 2 f Image Object so < f Image Object Inverted Reduced Real This could be used in a camera. Big object on small film Inverted Enlarged Real This could be used as a projector. Small slide on big screen Upright Enlarged Virtual This is a magnifying glass

Lens Equation In Front of Lens Behind Lens do F Object F f Image di

Example A 2. 0 cm high object is placed 5 cm in front of a +10 cm focal length lens. Where is the object located? Is it real or virtual? Find the height of the image. Image F F Object The image is upright, virtual, and enlarged! P. A.

Example A 4. 0 cm high object is placed 18 cm in front of a +8 cm focal length lens. Where is the object located? Is it real or virtual? Find the height of the image. F Object F