Conceptual Physics: pp ; Chapter 30

 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. ii rr 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)

 A few index values that we will be using often in class: (Pg. 15 in workbook) n glass = 1.50 n water = 1.33 n air = 1.00 n diamond = 2.42

 Light will NOT refract when;  1. the two materials have the same index  If the materials have the same index, the speed of light is the same in each, so no refraction takes place n=1.3

 Light will NOT refract when;  2. the light strikes perpendicular (normal) to the surface n=1.2 n=1.4

 Critical Angle- The angle of incidence that produces a 90º angle of refraction  (can ONLY be produced going from more to less optically dense)

 1. Light passing from less to greater index  Light bends toward the normal line n = 1.2 n = 1.5 Angle of incidence (measured from the normal)  i  r Angle of refraction

 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.

 Two Types of Lenses  1. Convex (converging)  2. Concave (diverging)  Lenses are simply rectangular and triangular prisms put together.

 When light passes through a triangular prism, it bends toward the thicker portion of the prism. n = 1.0 n = 1.5 n = 1.0 n = 1.5

 Light bends when it enters and unbends by the same amount when it exits the prism  The path is unchanged- it is simply displaced sideways.

 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. FF FF The image is real, inverted and smaller

 Have virtual foci. F F FF

 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)

 2 Types  1. Double convex  2. Double concave

 Converging lens  Examples:  Magnifying glasses  Microscopes  Correct farsightedness (hyperopia)

 Diverging Lens  Examples:  Peep hole  Correct nearsightedness (myopia)

 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

Object Distance Image Distance Larger/sma ller/same Erect/Inver ted Real/Virtua l