3D Printing LESSON PLAN PHYSICS 8,11: OPTICS

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1 INVESTIGATE RATIONALE Optics is commonly taught through the use of commercial optics kits that usually include a basic set of 2-4 geometric lenses (such as double convex or double concave). These lenses are often usually pre-mounted with the focal distances already indicated. The problem with such a kit is students never learn how to these factors has on the focal length. result, students will be able to: ent shapes, dimensions, and materials. As a Students are more engaged when they are able to use a 3D printer to develop their own optics equipment, in comparison to using commercial optics kits. As a result, students will not only develop a deeper understanding of optics but will also have gained the tools necessary to explore further questions as a result of the hands-on nature of the work. creation of new tasks, previously inconceivable. (

2 INVESTIGATE CONTEXT Vocabulary: Refraction Converging Lens Diverging Lens Optical Density Focal Point Focal Distance Background Knowledge/Key Ideas: Light moves through a vacuum at a speed of 3.0 x 10 8 This change in the speed of light also causes light to change directions when it travels from one material to another. This is known as refraction. The tendancy second. For a lens, light travels through air and enters the lens and is then refracted. If light rays are refracted so that they converge at a point behind the lens otherwise known as the focal point the lens is a converging lens. Double convex lenses are converging lenses. If light rays are refracted so that they diverge that is, light rays spread away from each other and do not meet up at a point behind the lens the lens is a diverging lens. Double concave lenses are diverging lenses. would make sense that the focal length of a lens would change depending on the material making up the lens. length if the lens where made wider or thinner, longer or shorter, or surface of the lens were made more or less curved? curvature on the focal length of a converging lens.

3 INVESTIGATE LEARNING OUTCOMES BC Science 8 Physical Science: Optics PLO C1: Demonstrate knowledge of the behaviour of waves - describe how waves are refracted when passing from one medium to another. PLO C2: Explain the properties of visible light - identify and describe the properties of visible light - demonstrate how visible light is refracted (e.g. bending of rays, diverging and converging lenses). Processes of Science BC Physics 11 Wave Motion and Geometrical Optics PLO B3: Analyse situations in which light is refracted - identify a lens as converging (convex) or diverging (concave) - conduct an experiment to determine the focal length of a convex lens. Skills, Methods, and Nature of Physics PLO A2: Apply the skills and methods of physics - systematically gather and organize data from experiements - produce and interpret graphs - verify relationships - use models to solve a variety of problems PLO A3: Represent and interpret information in graphic form PLO A4: Use models to explain how systems operate investigative procedures and research

4 DESIGN + MAKE 3DP Why are we designing lenses? order to do so, we need to accurately design lenses of varying radii of curvature and determine their focal lengths. What needs to be designed? 5 lenses. The minimum radius of curvature is 25mm, and each lens must have a radius of curvature that is at least 20mm smaller or larger than any other lens in their set. Also, the width of these lenses will be 30mm. How are we going to design the lenses? STEP 1: Use AutoCAD 123D to draw out a mold of the lens STEP 2: 3D print the lens molds STEP 3: Cast the lenses using gel wax.

5 DESIGN + MAKE 3DP: MODELING Instructions for designing a lens with 40mm radius of curvature: STEP 1: Using AutoCAD 123D 1. Open Autodesk 123D design software on your computer. 2. If you are using a 3 button mouse to control the cursor, know that the clicking the left button will allow you to select items, clicking and holding the scroll button will allow you to pan from side-to-side or up-and-down, and clicking and holding the right button will allow you to rotate the view side-to-side or up-and-down. Using the scroll feature or the scroll button will allow you to zoom-in and zoom-out. Unless otherwise stated, anytime we say click in our instructions indicates a click of the left button on the mouse. 3. Take a look at the screen view. Make sure the units indicated in the Units box on the lower right hand side of the screen says mm (millimetres). Change units to mm if not currently in mm. cursor to select the top view 5. Use the scroll wheel to zoom-out and click and hold on the scroll wheel to pan the view so that you are looking at the centre of the grid. Drawing the well 6. Move the cursor to the buttons at the top of your screen. Click on the Sketch icon and move to select Sketch Circle. 7. Before sketching the circle, you must click on the grid. Click on the grid, and click anywhere on the grid to indicate the centre of your circle. 8. Move your mouse until a diameter of 80mm is reached, click the left button, and then click on the Exit Sketch icon (the green box with the check mark) to complete the circle sketch. Alternatively, you can enter the circle diameter of 80mm by using the keypad on your keyboard, pressing enter once to lock in the dimension, and pressing ener a second time to exit sketch. 9. Move to the top of the screen and click on the Sketch icon. Select Polyline.

6 DESIGN + MAKE 3DP: MODELING 10. Click on the circle before you beginning drawing the line. NOTE: if you are modifying an object, you must click to select your object before starting any function so that the program knows that you are modifying the object and not starting a new one. Therefore, in this case, click on the circle before sketching to indicate that you are adding the line to the sketch and not drawing a separate unrelated line. 11. From the point on the circle that is directly to the right of the centre point or the circle, count 3 vertical grid lines to the left. Then, move up this vertical grid line and count 3 horizontal grid lines above the point where the circle intersects with this vertical gridline. Click this point to indicate the start of your polyline. Note: each grid line represents 5mm. 12. Move your cursor down the vertical gridline and click on the point that is 3 horizontal grid lines below the point where the circle meets the vertical gridline. Click on the Exit Sketch box to complete the line. 13. Click to select your object. You ll notice a square icon appears close to where you clicked on the circle. Hover over the box with your cursor and other options appear. Click on the Mirror icon. 14. Notice that a box titled Sketch Entities and a box titled Mirror Line appear. Make sure the Sketch Entities box is the one that is selected. Click on the circle to indicate that the circle is the object to be mirrored. 15. Click on the Mirror Line box. Click on the vertical line to select this to be your mirror. Click on the exit sketch box to complete mirror function. 16. Move to the top of the screen and click on the Sketch icon. Select Trim feature. 17. Click to select your object. Move the cursor over the curve you want to remove and click on the curve to remove it. 18. Click on the Exit Sketch icon when you have removed the curves so that a double convex object remains. This space represents the well you will pour the gel-wax into to create your lens.

7 DESIGN + MAKE 3DP: MODELING Making the rim of the mold 19. Move the cursor to the buttons at the top of your screen. Click on the Sketch icon and move to select Sketch Circle. 20. Click to select the lens well. Then, use the same point as the centre of your new circle. 21. Click the centre point and create a circle that is 83mm in diameter. Click Exit Sketch icon when done. 22. Click to select the 83mm circle you just created and perform the mirror function again. 23. Move the cursor to the buttons at the top of your screen. Click on the Sketch icon and move to select Trim. 24. Click to select your object and trim the curves like last time. What remains is a double convex within a larger double convex the space between will become the walls to the lens. Making the handles distance and hit enter. e line. This time, move the line slightly to the left. Using the 28. Move the cursor to the buttons at the top of your screen. Click on the Sketch icon and move to select Polyline. 29. Click to select the object. Using the Polyline function, draw straight lines to connect the ends of the 2 lines you created using the 30. Move the cursor to the buttons at the top of your screen. Click on the Sketch icon and move to select Trim. 31. Click to select the object. Use the Trim function to remove all the lines such that you are left with the following sketch. You should see a well that is surrounded by 2 identical rims that are mirror images of each other.

8 DESIGN + MAKE 3DP: MODELING Going to 3D with a 2D sketch 32. Move the cursor over the left rim so that the entire rim glows green. Click to select the left rim. 33. Holding down the Shift key, click to select the right rim as well. 34. Select the Extrude function. Using the keypad, enter 1.5mm. 35. You now have a 3D lens mold. We now need to separate the rims so that it will be easier to remove the molds once they are cast. 36. Move the cursor to the buttons at the top of your screen. Click on the Modify icon and move to select Split Solid. 37. Click to select the object as the Body to Split. 38. Click on the box that says Splitting Entity. Click to select the centre vertical line and hit enter. The 2 rims should now be split apart. 39. Click to select the right rim. Select the Move function, and click and hold on the arrow pointing to the right (this will move the rim to the right). Using a keypad, enter 3.0mm. 40. To modify the curvature of the lens molds, change the diameter of the circle you are drawing to create the well. That the radius is half the diameter of a circle; therefore, if you were to create another lens with a 60mm radius of curvature, you would need to sketch a circle with a 120mm diameter. When creating the rim, remember that the larger circle will be 3mm larger in diameter compared to the circle creating the well. 41. To modify the depth of the lens mold, change the value that is entered when using the Extrude function when going to 3D with a 2D sketch. 42. To modify the width of the lens mold, change the where the centre polyline line is drawn when creating the well.

9 DESIGN + MAKE: Designing a lens with 40mm radius of curvature, steps 3 to 22 (click on each image to enlarge)

10 DESIGN + MAKE: Designing a lens with 40mm radius of curvature, steps 22 to 39 (click on each image to enlarge)

11 DESIGN + MAKE 3DP: PRINTING STEP 2: 3D print the lens molds 1. On your computer, open Tinkerine Suite software. Insert SD card into computer Click the Settings button and click the down arrow to display all the options. For this alls: 3; Speed: Click the Slice button to start slicing the object. d. 6. Remove SD card from the computer. 7. Turn on Tinkerine 3D printer and insert into the printer control panel. 8. Click on knob, scroll down to Print from SD, and click on knob again. begin until the hotend is warm enough. 4 4 click on images to enlarge watch a video of the molds being printed 5

12 DESIGN + MAKE 3DP: CASTING STEP 3: Cast the lenses using gel wax. Before casting, you will need 2 binder clips for each mold, painter s tape, a sheet of parchment paper, and gel wax 1. Preheat oven to 230 F (110 C). 2. Cut some gel wax and place in a small, metal sauce pan or any other oven safe container. 3. Put pan/container in the oven and wait until gel wax has completed melted. 4. While waiting for the gel wax to melt, apply painter s tape to the inside of your molds. The painter s tape will make it easier for the lens to be removed from the molds later on. 5. Join the molds together by using binder clips to fasten the ends. Place completed mold on parchment paper. 6. When the gel wax has melted completely, take pan out of the oven and pour wax into the molds. 7. Let cool for 10 minutes. 8. When it looks like the wax has settled, unfasten the clips and gently peel the molds away from the gel. You should be left with a clear lens. 9. Clean up: instead of washing out any leftover wax, let the wax cool in the container and peel wax from container when cooled. Save wax for future use.

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14 EVALUATE STUDENT HANDOUT Optics Investigation Purpose: Materials: Ray boxes Rulers 5 gel wax lenses of varying curvature (NOTE: lenses should each have a radius of curvature that is at least 20mm larger or smaller than the other lenses to be tested). Procedure: 1. Set up the equipment as in Figure 1. The zero line of the ruler should line up with the imaginary centre line of the lens. towards lens. Observe where the beams of light converge after the light passes through the lens. This point is the focal point. 3. In table 1, record the measurement along the ruler as to how far the focal point is from the zero line. This is the focal length. ent radius of curvature. Repeat steps 1-3. Continue switching out lenses until all your lenses have been tested.

15 EVALUATE STUDENT HANDOUT Data Table 1 Radius of Curvature Focal Length Plots On a sheet of graph paper, plot a graph. The radius of curvature is displayed on the x-axis and the focal e plotted. Analysis 2. With reference to your graph, predict the focal length of a gel wax lens with a radius of curvature of: (a) 15mm, (b) 95mm, and (c) 105mm 3. A gel-wax lens of unknown radius of curvature is tested and the focal length is measured at 2.7cm. What is the radius of curvature of the lens? 4. After light beams pass through your gel-wax lens, the light beams may not be as sharp as before (that is, they may tend to spread out more). What is the cause of this spreading?

16 ADAPT APPLICATION Compound microscopes use a system of 2 or more lenses to magnify objects. Refer to the following instructions on how to build and modify your own microscope (click this link), and use what you have learned from this lesson to design and cast the necessary lenses. FUTURE STUDY Using what you have learned from this lesson, design and cast your own lenses to test the following: 1. What happens to light rays as they pass through double concave lenses or lenses that are asymmetrical such as concavo-convex and plano-concave lenses? 2. Compared to gel-wax lenses, would the focal length be longer or shorter if the lenses were made of Jell-O or Ice? 3. How would focal length change if the width of each gel-wax lens were made shorter or longer?