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First day ideas about light

August 31, 2011

In today’s inquiry course, we began our investigation about light:

At some point, we were discussing what it would look like if you were sitting in a dark room looking out into the hallway, and your friend was shining a flashlight down the hall. The major predictions that came up were these:

Idea #1: You’d see a “concentrated” beam of light. Some thought this would be like a narrow beam, others thought it would look bigger the farther it goes down the hall away from the flashlight (like a cone of light).

Idea #2: You’d see a beam of light, but that some of the light would “spill” or “leak” into the room you are in. That light  that spilled over would light up some of the room by the dorr, but they didn’t think it would be able to go around and light the whole room (like the corners).

Ideas #3: Everything in the hallway would just be “lit up” inside, allowing you to see what’s inside. Some said it would be brighter the closer you are to the flashlight (and dimmer farther away) in a long hallway, but that it would appear equally bright in a smaller hallway. Some with this idea talked about the “glow” of the light filling the space, while others talked about the light bouncing around off the walls to get everything lit up.

Idea #4: You’d mostly just see dust or particles shining in the air. Some thought you’d see dust only with a faint light (or light far from flashlight), because a strong light would just show the concentrated beam. Others thought that you would need a bright light in order to see the dust, because the light needs to reflect off the dust strongly.

 Idea #5: The side walls of the hallway would only would be dimly lit, but at very the end of the hallway there should a spot of light on the wall. If you were just looking in but not down the hallway, you’d see the dimly lit walls due to “ambient” light everywhere. But if you looked down the hall, you’d see the spot of light down at the end.

During and after observations, students noticed and wanted to talk about a variety of things, including

(1) The fact that they didn’t see a beam of light. This was the most common reaction, and several students talked about how they must have been thinking about like “cartoon” light.

(2) The fact that they did see some light get out of the hallway and into the room through the door, but it didn’t leak through, like they had expected. They talked about how the door angled the light in a particular way based on where the flashlight was located. On group mentioned how we only see the light out of the room because it hit the floor–we couldn’t see it traveling to the floor.

(3) They also saw that there was a specific starting place where the walls began to be lit, and the boundary of that lit places was curved. There were ideas about how the mirror in the flashlight causes this curviness. Other thought the circular shape of the flashlight hole was the cause. Some thought it might be both.

(4) There was also some discussion about whether the dark spaces were completely dark or just somewhat darker than the bright regions. One group explained that it didn’t seem completely dar (just much darker), and that maybe light was reflecting off the walls and getting back to those areas that don’t get direct light. This started to touch upon an idea that the reflected light might be dimmer than direct light.

(5) Some students noticed that there was a circular spot down at the end, and they used this as evidence that there must be a beam even though we can’t see it until it hits the wall. Other students said that they didn’t want to call such an “invisible beam” a beam, but something else instead. This conversation also started to touch upon ideas about what the mirror was doing. Some thought the mirror was “funneling” the light some how, making it more concentrated into a beam, while others thought the mirror was just making the light that would have gone backwards go forward.

Students also had various other questions, including :

(1) Why is the lit space curved the way it is?

(2) What would be different if we just used a regular bulb instead of a flashlight? Would different shaped bulbs make a difference?

(3) What would change if the back end of the hallway was a mirror? Would the dark spots behind the flashlight now be more lit?

(4) The shape of the light that made it out of the hallway was affected by the shape of the door. Would a circular hole make circular spot of light? Triangle hole triangular?

(5) What would change if we added lots of the dust? Would we see a beam then?

We have a lots of good starting ideas and questions, and there are lot of places that I want to work on getting them to clarify and be more specific about what they are thinking and why. I’m excited to see where we go, but I’ll have to wait a week.

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