Presentation on theme: "Conceptual Physics: pp. 448-459; Chapter 30. Refraction-The bending of a wave as it enters a new medium Medium-The material the wave travels through."— Presentation transcript:
Refraction-The bending of a wave as it enters a new medium Medium-The material the wave travels through Why does light refract? It enters the new medium at an angle It changes speed
Angle of incidence ( i or θ i ) -The angle between the incident ray and the normal line Angle of refraction ( r or θ r ) -The angle between the refracted ray and normal line
Normal line – an imaginary line perpendicular to where the light strikes the interface. ii rr Imaginary line showing the path that the light would take if it could go straight. (used as a reference line) Interface – the boundary between substances Incident ray Refracted ray
Index of refraction (n): the ratio of the speed of light in a vacuum to the speed of light in that medium Example: n glass = speed of light in vacuum speed of light in glass n glass = 3.00 x 10 8 m/s 2.00 x 10 8 m/s n glass = 1.50
The higher the n value (index of refraction) The slower the light will travel through the material The greater the optical density The more light will refract (bend)
2a. Light passing from greater to lesser index Light bends away from the normal line n = 1.6 n = 1.3 ( i is less than critical angle) As the angle of incidence increases, the angle of refraction also increases and the refracted ray moves closer to the interface.
2b. Light passing from greater to lesser index Light travels along interface n = 1.6 n = 1.3 ( i equals / at critical angle )
2c. Light passing from greater to lesser index Total internal reflection n = 1.6 n = 1.3 ( i is greater than critical angle) The light doesn’t refract. Instead, it reflects back into the first substance. This is how fiber optics work.
Putting the triangular and rectangular prisms produce the 2 types of lenses (double concave and double convex)
Focal point-The point where refracted rays from parallel incident rays intersect Focal length-The distance between the focal point and the lens Real image-An image formed from the intersection of actual light rays Virtual image-An image that is NOT formed by the intersection of actual light rays
Have real foci Two focal points at equal distances on each side of the lens F F F F
1. Draw the ray parallel to the axis, hit the lens, and refract through the focal point on the other side. 2. Draw the ray through the center of the lens without bending. 3. Draw the ray through the first focal point, hit the lens, and refract parallel to the axis. FF FF The image is real, inverted and smaller
1. Draw the ray parallel to the axis, hit the lens, and refract away from the first focal point. 2. Draw the ray through the center of the lens without refracting. 3. Draw the ray toward the focal point on the other side of the lens, hit the lens, and refract parallel to the axis.
The image with a concave lens will always be smaller, upright, and virtual It will also always be found between the focal point and the lens. (similar to a convex mirror)
Rules to determine whether the image is real or virtual: 1. Real images are always inverted 2. Virtual images are upright. (Except for combinations of lenses)
Light traveling through air hits glass at a 28 degree angle. What is the refracted angle? 1. Draw a picture 2. List variables 3. Write formula 4. Substitute 5. Show some work 6. Solve and label 7. Check if the answer is reasonable!!!
1. Light strikes the surface of a piece of glass from air with an incident angle of 70 ◦. What is the angle of refraction? Person #1: Draw a diagram Person #2:List the variables Person #1: Write the formula and substitute Person #2: Solve
2. Calculate the critical angle for the substances water and glass. Person #2: Draw a diagram Person #1: List the variables Person #2: Write the formula and substitute Person #1: Solve