Lab 8 - Reflection and Refraction

Lab 8: Reflection and Refraction Full Name(s) of group member(s): Mckenna Fears Chad Wilson Alyanna Rodelas Titan Harker Joseph Dougherty Learning goals: Students will be able to:  Predict the position and size of an image produced by a mirror using ray diagrams  Identify the orientation and magnification of an image  Identify the differences between a real and virtual image  Calculate the size and position of an image produced by a mirror  Measure the angle of incidence and refraction to calculate the index of refraction When light (wave) travelling in one medium encounters a boundary of another medium, part of the light may bounce back, or reflect, to the same medium and some part of the light may pass into the second medium, called refraction. In this lab, we will study reflection and refraction of light. First, we will study the formation of images by different mirrors. Images are formed by mirrors due to the reflection of light originated from an object. Images may be real or virtual, upright or inverted, and diminished or enlarged. We can locate and characterize the images by tracing the reflected rays. The reflected ray makes an angle with the normal to the surface called the angle of reflection, θ r . The law of reflection states that the angle of reflection, θ r , equals the angle of incidence, θ i . The normal, incident ray and reflected ray all lie in the same plane. Even if the surface of the mirror is curved, the angle of incidence and angle of reflection will still be equal along a line that is normal to the surface. When parallel rays are incident on a concave mirror, the reflected rays converge to a focal point, a concave mirror is also called a converging mirror. In the case of a convex mirror, parallel rays are diverged from the mirror after reflection and appear to come from a virtual focal point, hence it is also called a diverging mirror. The distance from the mirror to the focal point is called focal length, f . We can approximate the focal length in a spherical mirror to be equal to half of the radius of curvature, f = r / 2 . For spherical mirrors, the relationship between object distance d o , image distance, d i , and focal length f is given by mirror equation: 1 f = 1 d o + 1 d i

The magnification of the image is given by: m = h i h o = − d i d o Part I: Verify the Law of Reflection 1. Using a plane mirror and a laser, verify the Law of Reflection by tracing the incident and reflected rays for at least two different angles of incidence. Compare the angle of incidence and the angle of reflection for both. Discuss your results. The angle of incidence and angle of reflection are equal to one another. This is the Law of Reflection. 2. Now reflect light from some other flat, smooth surface, and verify if the Law of Reflection only apply to what we commonly call mirrors. Discuss your findings. The angles are still equal as long as the light is reflecting off of a smooth surface. The surface must be smooth so that the light bounces off in a uniform matter, if not smooth the light will diffuse. 3. Reflect the light from a curved surface and verify if the Law of Reflection still applies. Discuss your findings. When light reflects off a curved surface, the law of reflection works because if you take a tangent to the point where the light hits, it bounces off that tangent symmetrically.

2. Trace three rays all from the same point on the object for a concave mirror in the diagram below: a. Draw the first ray from the top of the image horizontally toward the mirror. When this ray reflects from the mirror, it’s reflection will appear to be coming from the focal point. b. Draw the second ray from the top of the image directly toward the center of curvature. This ray will reflect directly back on itself. Trace back the reflection to the center of curvature, point c . c. Draw the third ray from the top of the image toward the focal point. This ray will reflect horizontally. d. Trace back each of the reflected rays behind the mirror. e. Find the point where all three of your reflected rays intersect. This point corresponds to the same point on the image that they originated from on the object. With the object oriented so that the bottom is along the center line, the bottom of the image will also fall on the centerline. Draw the image. f. Is the image upright or inverted? Upright g. Is the image reduced, enlarged, or the same height? Reduced h. Is the image Real or virtual? Virtual Open the “Spherical Mirror Simulation”. https://ophysics.com/l11.html In the simulation, you have an object that is placed in front of a concave mirror. 3. Compare the rays and image that you drew in question 1 to the initial settings in the simulation. Include a screen shot of the simulation.

7. Using the simulation, compare the Size and shape of the object and image when the object is placed in different locations near a spherical mirror. Complete the table below: Type of mirror Position of Object Real or Virtual Image? Upright or Inverted Image? Enlarged, Reduced, or Same size image? Concave Beyond Center of Curvature  Real Inverted  Enlarged  Concave Exactly at CC Virtual  Upright  Reduced  Concave Between CC and f Virtual  Upright   Reduced Concave Exactly at f No image No image No image  Concave Between f and mirror Virtual  Upright  Reduced  Convex 2 Virtual  Upright  Enlarged   Convex 4 Virtual  Upright  Enlarged   Convex 6 Virtual  Upright  Enlarged   Convex 8 Virtual  Upright  Enlarged  

Part III: Refraction When a ray of light strikes a surface separating one medium from another, it can undergo reflection and/or refraction at the interface. The figure shown the angle of the reflected ray, θ r , and of the refracted ray, θ R , are related to the incident angle, θ i ,by θ i = θ r , and n i sin ( θ i ) = n R sin ( θ R ) where all angles are measured in degrees with respect to the normal, and n 1 and n 2 are the indices of refraction of the incident and refracted beam media as shown. Study Snell’s Law: 1. Use Snell’s law to calculate the index of refraction of a glass or plastic block by tracing and measuring incident and refracted rays for at least three different incident angles. Compare and discuss your three results. Trial Incident Refracted 1 10 9 2 20 18 3 30 27 The incident and refracted angles are very close to one another, this means that the light slightly refracted when it went through the glass box. 2. Use Snell’s law to calculate the index of refraction of a liquid. Using the rectangular plastic box, measure the index of refraction of the liquid by tracing incident and refracted rays for at least three different incident angles. Trial Incident Refracted 1 20 10 2 30 20 3 40 30 The refracted angle was 10 degrees less than the incident angle for all trials. 3. Using the semicircular plastic dish, measure the index of refraction of your chosen liquid, to verify that Snell’s Law applies, even to curved surfaces. I promise I did it 