Refraction is the change in direction of a wave when it passes from one medium to another with a different speed. The index of refraction is the ratio of light's speed in a vacuum to its speed in a medium, and it determines how much light will bend at the boundary. Snell's law relates the sines of the angles of incidence and refraction to the indices of refraction. Total internal reflection occurs when light travels from a denser to a less dense medium at an angle greater than the critical angle, causing the light to be reflected back into the denser medium. Converging lenses bring light rays passing through the focal point to a focus on the opposite side, while diverging lenses spread out light rays

1. REFRACTION, LENSES, & SIGHT

2. REFRACTION
• The change in direction of a wave as is crosses the boundary
between two media in which the wave travels at different speeds.

3. INDEX OF REFRACTION
• The ratio of the speed of light in a vacuum to the
speed of light in a medium under consideration.

4. INDEX OF REFRACTION
material
in
light
of
speed
vacuum
in
light
of
speed
n

5. • C < V air < V liquid < V solid
• C is the speed of light in Vacuum

6. SNELL’S LAW
2
2
1
1 sin
sin 
 n
n 

9. TOTAL INTERNAL REFLECTION
• When the light goes from a medium that has more
dense to a medium that has less dense the refracted
ray goes far from the normal and makes an angle of
refraction =90
• The angle that makes this case is called the
critical angle

10. TOTAL INTERNAL REFLECTION

11. • When the incident angle is more than the critical angle it makes
the case of total internal reflection

12. INDEX OF REFRACTION
Material Index of Refraction
Vacuum 1.0000
Air 1.0003
Ice 1.3100
Water 1.3330
Ethyl Alcohol 1.3600
Plexiglas 1.5100
Crown Glass 1.5200
Light Flint Glass 1.5800
Dense Flint Glass 1.6600
Zircon 1.9230
Diamond 2.4170
Rutile 2.9070
Gallium phosphide 3.5000

14. LENSES

15. CONVERGING LENS

16. RULES FOR CONVERGING LENSES
1) Any incident ray traveling parallel to the
principal axis of a converging lens will refract
through the lens and travel through the focal
point on the opposite side of the lens.
2) Any incident ray traveling through the focal
point on the way to the lens will refract through
the lens and travel parallel to the principal axis.
3) An incident ray which passes through the center
of the lens will in effect continue in the same
direction that it had when it entered the lens.

17. IMAGE FORMATION BY CONVERGING
LENS

18. DIVERGING LENS

19. RULES FOR DIVERGING LENSES
1) Any incident ray traveling parallel to the
principal axis of a diverging lens will refract
through the lens and travel in line with the focal
point (i.e., in a direction such that its extension
will pass through the focal point).
2) Any incident ray traveling towards the focal
point on the way to the lens will refract through
the lens and travel parallel to the principal axis.
3) An incident ray which passes through the center
of the lens will in effect continue in the same
direction that it had when it entered the lens.

20. DIVERGING LENS IMAGE FORMATION
Always Virtual, Smaller, and Right-Side Up

21. THE HUMAN EYE