Spring 2014 Day 2

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Exploring Physics (continued) By Emma Grobart
Using Powerful Ideas to Develop an Explanation of an Intriguing Phenomenon
To make a pinhole camera, you need a cardboard tube, foil, wax paper, two rubber bands and something to make a small pinhole in the foil like, such as a thumbtack. First you take the small sheet of foil and wrap it around one end of the cardboard tube. Make sure you fasten it by rubber banding it to the cardboard tube. Then, take the small sheet of wax paper and repeat the process done with the foil. Next, take thumbtack and poke a small hole in the foil. Your pinhole camera is now complete! To see the light source as clearly as possible, the room should be dark and the light source should be bright and its shape should be distinct. A light bulb works perfectly fine.

As seen in Figure 1, you should hold the pinhole camera relatively close to light source. Make sure that the foil side is facing the light and the wax paper is facing you. When you look at the wax paper, the light source should appear upside down. This is the “Aha” moment at which we are going to be taking a closer look at.

Figure 1. Looking at a light source through a pinhole camera.

Figure 2 models the process of how the image appears upside down. As discussed before, when the light leaves the bulb, it travels in all directions. When you see the image in the wax paper, only a few of the rays of light are going through the pinhole. In Figure 2, you can see that light from the top, middle and bottom of the bulb travel through the pinhole in a straight line. The rays from the top of the light bulb project straight through the pinhole to the bottom of the wax paper screen where they form a projection of the top of the light bulb on the bottom of the screen. The rays from the bottom of the light bulb project straight through the pinhole to the top of the wax paper screen where they form a projection of the bottom of the light bulb on the top of the screen. The rays from the middle of the light bulb continue straight through the pinhole to the middle of the wax paper where the projection is on the middle of the screen.

Figure 2. Ray diagram showing how the image appears upside down.

To mix things up, I decided to see what would happen if there were multiple holes in the foil. I predicted that there would either be multiple images projected or that the image would be broken up so that each hole would project a certain part of the light source. The first time I held the camera up to the light bulb, I was further away, and multiple images projected onto the wax. When I moved closer to the light bulb, the images became blurry and started overlapping images.

A question that I still have about pinhole phenomena is something that my group in class was exploring. We tried to figure out how to project an image so it would be accurate to its original source. This is a lot harder than it sounds and we are still talking through different solutions.

My roommate and I explored the pinhole phenomena using the pinhole camera made in class. Instead of a regular light bulb, we used a colorful nightlight. At first I was worried about the nightlight being dim, but it worked out very well and the results were exciting to look at! My roommate enjoys photography so I thought he would find this activity interesting and relevant to his hobby. Surprisingly he did not have any experience with a pinhole camera, but as the activity progressed he started to draw connections between pinhole cameras and cameras used in today’s world. My roommate was surprised that the projection of the image appeared to be upside down. I did not want to spoil any curiosity, so I allowed him private reasoning time to conjure thought. By giving him space to talk things out on his own and reason through his thoughts, he ended up coming to the conclusion on his own without any coaxing whatsoever. He talked his way through the projection process and used reasoning to determine whether or not his perditions were logically valid. His first reaction was that it had to do with the positioning and angle of where the camera and nightlight was located but as he played around with the positioning of the camera, he quickly realized that that was irrelevant to the display image. His second thought came from the idea of an image from a projector. His thought was that if you were inside the pinhole camera looking at the wax paper, you would see the correct image of the nightlight, but because we are on the outside of the pinhole camera, we are seeing the reverse image. As he gave himself more time to think about the thought, he realized that that would not be accurate because the image appears upside down instead of in reverse. He finally came to a conclusion by thinking about how the light travels and where it is going. From previous knowledge that light travels in a straight line, he made the connection and reasoned that the image appeared upside down because the light travels into the pinhole and continues to travel in the same direction. What I learned about fostering science learning and teaching is to break the activity into sections so the science learner will have a solid grip on the activity and why it is relevant. I started off by explaining how a pinhole camera was made. I then explained how to use the pinhole camera and then I facilitated my roommates learning experience by answering and asking questions for him to gain a deeper understanding. All of these aspects allowed me to reflect on my knowledge as well as conduct an efficient and powerful learning experience.

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