Unit 1: Exploring the Nature of Light Phenomena
IV. Using Central Ideas to Develop an Explanation for Intriguing Phenomena
So far we have developed two central ideas based on evidence about the nature of light:
Light leaves most sources in many directions.
Light can be envisioned as rays traveling in straight lines.
These ideas form an initial conceptual model of light. These are ideas that most people find easy to understand; they even are evident in the art of young children, who typically draw a sun as a circle with straight rays streaming out from the circle. Figure 1.10 is an example.
You can use these two central ideas to explain intriguing phenomena such as what happens when light passes through a tiny pinhole.
A. Exploring pinhole phenomena
Question 1.9 What happens when light passes through a tiny pinhole and shines on a screen?
There are many ways to explore what happens when light passes through a tiny pinhole. One way involves making a pinhole camera with materials typically available at home. This is called a camera but no photograph is made as no film is used in this exploration.
Equipment for each student: a toilet paper or paper towel roll, square piece of wax paper, square piece of aluminum foil, two rubber bands. Equipment for each small group: a push pin. A meter stick (or yard stick) and ruler also will be helpful in developing an explanation of what one sees when looking through such a pinhole camera at a bright light bulb in a dark room.
In a remote learning situation, students might have access to a paper cup or a cardboard box with a open end such as a snack box whose bottom can be made light tight with duct tape. Possible substitutions for the wax paper include a translucent cereal box liner or plastic vegetable bag from a grocery store to cover the open end. A chocolate bar liner might be a source of aluminum foil if a student has an empty paper roll with both open ends.
A student described making such a pinhole camera as follows:
First I laid the wax paper over one opening of the toilet paper roll and snuggly wrapped the edges down and secured the wax paper with a rubber band. I then laid the aluminum foil on the other end of the toilet paper roll and secured the edges of the aluminum foil with a rubber band. I took a push pin and made a single hole in the middle of the aluminum foil. I held the camera up so that the light from the light bulb on the table could shine through the pinhole in the aluminum foil and the wax paper faced me.
Physics student, Spring 2016
- Make a pinhole camera as described above.
- When you look through a pinhole camera at a bright light bulb in a dark room, what do you think you will see on the wax paper screen? Record your prediction and your reasoning in the Before section of your physics notebook page.
- After making a pinhole camera, darken the room and turn on a light bulb without a shade. Look at the light bulb through the pinhole camera. Hold the camera away from your face and point th