Total internal reflection

2. Total internal reflection n1 > n2 increase n1 until the refracted angle=90

3. Critical Angle the incident angle is called the critical angle

4. Example

5. Total Internal Reflection (Example) Can light passing from crown glass into air be totally internally reflected? If so, what is the critical angle? n1=1.52 n2=1 YES!!! since n1>n2 Crown Glass Air

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

7. 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.

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

9. Image formation by lenses Types of lenses

10. Lensmaker’s Equation (for a thin lens)

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

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

13. Three Easiest Rays To Sketch Image F Object 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, invertedandenlarged(in this case).

14. 3 Cases (converging lens) Image Object Image Image Object Object so>2f Inverted Reduced Real This could be used in a camera. Big object on small film so between f & 2f Inverted Enlarged Real This could be used as a projector. Small slide on big screen so < f Upright Enlarged Virtual This is a magnifying glass

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

16. 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 P.A. Object F The image is upright, virtual, and enlarged!

17. 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