Modifications to Physics by Inquiry, Volume I, Light and Color in Part A: Light and shadows, Sections 1, 2, 3 (pp )

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1 PHYSICS 160 SPRING 2011 Modifications to Physics by Inquiry, Volume I, Light and Color in Part A: Light and shadows, Sections 1, 2, 3 (pp ) CHECKs: 1.4B SHAD. Section 1. Introduction to light (pp ) 1) Turn to page 225 in Volume I 2) In Experiment 1.1 instead of using a small bulb, two batteries, and connecting wires, use Minimaglites with their end reflector assemblies removed to expose the small bulb. One can set these up as candles. Instead of using covers made from construction paper, use the Ping-Pong balls with holes in them. In part A, do the top view diagram on handout #1. In part B turn off table lamp for best results. Skip pact C at this point. We will revisit this discussion later. 3) Before leaving Experiment 1.1, discuss with your teammates and define the terms light source and point light source. Is the light bulb you used in this experiment a point light source or not? Explain. 4) Omit Experiment ) In Experiment 1.3 the room lights will be on. The light bulb being asked about is the light bulb of the minimaglite. To make it unlighted and uncovered, you must take the batteries out by unscrewing the end. In parts B and C where it says to use a flashlight, use a conventional flashlight such as the colored ones available at your stations. Ignore the request in B to place a mask on the flashlight. 6) Delete the request for a CHECK at the end of 1.3 and instead write up your answer to 1.4B on the bottom of page 227 as the first CHECK. You do not need to do Exercise 1.4A. 7) If you feel good about your CHECK on 1.4B, omit Exercise ) In Experiment 1.6, a flashlight with a mask simply provides a narrow beam of light going down the hall. We will use another arrangement to get the same effect. Before doing the check of 1.6, revisit part C of Experiment 1.1. Can you see a beam in vacuum from the side? What happens if the beam from a flash light hits your eye (do not try this with a laser beam)? A beam is composed of light rays. What is a light ray? Sketch a few (three to four) light rays for both of the cases in handout #2. A light ray must be originated from what type of light source? Can you see a light ray from the side? What happens if a light ray hits your eye? Section 2. Light sources, masks, and screens (pp ) 7) In Section 2 and later wherever the curriculum materials call for use of small bulbs, instead use Minimaglites set up as candles, where they act as small sources of light. BE SURE TO MAKE A PREDICTION BASED ON YOUR CURRENT KNOWLEDGE BEFORE DOING EACH EXPERIMENT. 8) Instead of doing Experiment 2.2, answer the following questions: (a) What is the geometric shape of a light ray? (b) How many light rays are emitted from a point light source? In what directions? (c) Revisit check 1.4, restate the conditions necessary for you to be able to see a point object with the idea of light ray.

2 (d) In handout # 3, sketch a few light rays from the point light source that are blocked (or absorbed) by the mask. Sketch a few light rays from the point light source that go through the hole in the mask and hit the screen, shade the region formed by these thru light rays. (e) According to your work in handout #3, explain what happens if the point light source is (i) moved upward, (ii) moved further away from the screen. 9) In Experiment 2.3 part C, think about and do the experiment with a 1-cm circular hole rather than a triangular hole and for which, as the mask tilts or rotates, the center of the hole is kept in the same place. Also, add a CHECK at the end of 2.3C. Be sure to summarize your observations for 2.3 parts A, B, and C. 10) Experiment 2.4 is as an Exercise and not an Experiment. We will not actually use a mask with a 4-cm hole in an experiment, but rather make a careful diagram on a graph paper and draw conclusions from it. Only do part A of 2.4 omit parts B and C. Read the statement near the bottom of page 232 about how to consider the light source. 11) In Experiment 2.5, change the hole diameter to 10 cm instead of the written 1 cm in diameter. 12) Change part A of 2.5 to the following: Make a scale diagram on a graph paper using the dimensions shown for this situation. [Consider using a scale of 1 cm in the diagram per 5 cm actual size. Why?] Then use the diagram in the same way you used the diagram in 2.4 to find the size of the bright region. 13) Omit parts B and C and D of Experiment 2.5. Remember to check your prediction with an experiment! 14) Skip to Exercise 2.6 and again approach the problem using scale diagrams rather than similar triangles. 15) The CHECK for Exercise 2.6 should cover 2.4, 2.5, and ) In Experiment 2.7 use a 1-cm hole. Before you do part B, make sure you know the correspondence between the light bulbs and their projections. You can confirm this by moving one of the light bulb and see which one of the two projections moves also. Explain your observation. 17) Repeat part B with the bulbs very close together. Discuss with your teammates what an extended light source is. An extended light sourced is composed of what? 18) In parts D and E include in your prediction the shape and size and orientation of what you would see on the screen. Perspective views in your drawings are better than the suggested top and side views. 19) In the CHECK at the end of Experiment 2.7 include a discussion of how what you learned in part C affects your answers to parts D and E. 20) In Experiment 2.8 omit parts A, B, D. In part C, use a scale diagram to achieve a solution, and check your prediction. Also think about how you could make the bright region on the screen taller and check this prediction. Move the CHECK off the end of 2.8 to the end of 2.9, where it should read Discuss your results to Experiments 2.8C and 2.9 with a staff member. 21) In Experiment 2.9 part B, use a club-shaped hole ( as in cards) rather than a star-shaped hole. 22) In Experiment 2.9 part A, B, C, in your predictions and observations note the height and width of what you would see on the screen. Discuss in terms of what you learned in Experiment 2.7C

3 about how to consider a long filament bulb. Describe your prediction to an instructor for part C before doing the experiment using a 100 watt bulb. Creating shadows 21) After the check on 2.9 do these activities on creating shadows. 1. In a darkened room shine a minimaglite (with the cap on) towards a blank wall. 2. Using your hands, see how many different sensible shapes and figures you can make. 3. Now repeat the experiment except have the cap of the minimaglite off, so that it functions as a point source. Where is it darkest in your shadow? Why? 4. Cut out some figures from construction paper and tape them to a Popsicle stick. 5. Move them closer and farther away from the minimaglite. What happens to your shadow when you move your hands towards or away from the minimaglite? 22) Add this SHADOWS CHECK: Does making shadows involve the same principles of the behavior of light that govern the making of bright spots using holes in masks? 23) here.

4 Handout #1 ping pong ball is the light bulb. Shade the area to show where you need to place your eye in order to see the bulb.

5 Handout #2 Case 1: Flash light Case 2: Laser

6 Handout #3 point light source mask screen