Optics 1 - Activities with Light Rays Purpose of this Minilab Apply the basics of ray tracing to learn about reflection and refraction of light.

Optics 1 - Activities with Light Rays Activity 1: Light Reflection at Plane Surfaces nini ntnt Index of refraction of the two materials Angle of incidence Angle of reflection Angle of transmission (refraction)

Optics 1 - Activities with Light Rays Law of Reflection: Snell’s Law of Refraction: Incident, reflected, and transmitted ray lie in one plane. …..the laws…..

Optics 1 - Activities with Light Rays Checking the law of reflection with a plane mirror 00 45  90  135  180  135  Light Source Polar graph paper ii rr Mirror

Optics 1 - Activities with Light Rays Measuring refraction 00 45  90  135  180  135  Light Source Polar graph paper ii tt Semicircular lens Light must hit the center of the flat side Use Snell’s law to determine n plastic. n plastic

Optics 1 - Activities with Light Rays Measuring angle of total internal reflection 00 45  90  135  180  135  Light Source Polar graph paper  crit Semicircular lens Light must hit the center of the flat side

Optics 1 - Activities with Light Rays Snell’s Law for Critical Angle =1

Optics 1 - Activities with Light Rays Light beam displacement by plane parallel plate Light Source ii tt d t

Optics 1 - Activities with Light Rays 00 45  90  135  180  135  Polar graph paper Light beam displacement by plane parallel plate Light Source ii tt d Trace light ray on polar graph paper. Outline location of rectangular plastic on paper. Measure angles  i and  t. Measure widths d and t. t Let the beam hit the rectangle in center of the polar paper

Optics 1 - Activities with Light Rays Light beam displacement by plane parallel plate Use one incident angle  i (and corresponding  t and d and t)  calculate n. Use this calculated n to predict the displacement d for a different incident angle. (Hint: You will also need to use Snell’s Law for this calculation.) Verify experimentally d for the new angle.

Optics 1 - Activities with Light Rays 180  Polar graph paper R 00 45  90  135  Move mirror until curvature matches the curvature on polar graph paper. then measure R as shown. Activity 2: Reflection and Refraction at Spherical Surfaces – Getting the Radius of Curvature

Optics 1 - Activities with Light Rays Finding the focal point of the concave mirror Regular graph paper: Trace the rays and determine f. Light Source parallel rays f

Optics 1 - Activities with Light Rays Finding the focal point of the convex mirror Regular graph paper: Trace the rays and determine f. Light Source parallel rays f Extend the light rays backward to where they seem to come from. Virtual image (isn’t really there).

Optics 1 - Activities with Light Rays Imaging with the convex mirror Regular graph paper: Trace the rays and determine f. P Light Source Semicircular or Circular lens Here is our object point S

Optics 1 - Activities with Light Rays Thin Lens Equation (how to calculate focal length from the radii of a lens and it’s index of refraction) Each lens has two interface with the air (#1 and #2). Interface #1 is the one that is encountered by the light when entering the lens. Interface #2 is the one that is encountered by the light when exiting the lens. Interface #1 has radius R 1. Interface #2 has radius R 2.

Optics 1 - Activities with Light Rays Thin Lens Equation (how to calculate focal length from the radii of a lens and it’s index of refraction) Sign rules for R 1 : R 1 positive R 1 negative R 2 negative R 2 positive

Optics 1 - Activities with Light Rays Example of using the lens equation A double concave lens (concave on interface #1 and also on #2) with both radii being 5cm and the index of refraction n=1.65 :  R 1 = - 5 cm and R 2 = + 5 cm 

Optics 1 - Activities with Light Rays The Imaging Equation for Lenses and Mirrors S: Object Distance P: Image Distance f: Focal Length For Mirrors:where R = Radius of Mirror

Optics 1 - Activities with Light Rays Sign Rules For Lenses and Mirrors Convex Lens: + Concave Lens: - Convex Mirror: - Concave Mirror: + f Real objects: S is positive Virtual objects: S is negative Real images: P is positive Virtual images: P is negative Means: a positive number Most objects are real.

Optics 1 - Activities with Light Rays Example of signs for f, S, and P P Light Source S Real object Virtual image positivenegative Convex mirror: f is negative

Optics 1 - Activities with Light Rays Using the Desk Lamp Dimmer Lamp Plug (black) must be plugged into dimmer plug. Dimmer plug (white) must be plugged into power outlet. On/Off switch of lamp