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Rules for Light

February 10, 2012

In Inquiry class, we spent most of the day trying to agree on “rules for light”. Here’s what agreed to:

(A) The path taken by light is straight

  • This means that light doesn’t curve around things and that’s it not wavy
  • We discussed how shadows and tanning are good everyday examples of this
  • A more contrived, but strong piece of evidence, is how a bulb held high shines down through a hole, and vice versa.

(B) There are many (maybe even infinite) paths of light going out in all directions from a source of light

  • In all directions means that light doesn’t shoot out in a beam with all the rays going straight together.
  • We talked about how a ceiling light lights up the whole room
  • There was some discussion a solar eclipse, and how that blocks the rays going toward the earth, which is why it gets dark, but there must be rays going in other directions. We wondered if we could see those rays going in other directions during a solar eclipse.

(C) When light hits a surface or an object it must either bounce (go off somewhere else) or be absorbed (stops), or possibly both

  • We discussed tanning as a good example of light absorbing
  • We discussed that word “bend” shouldn’t be used to describe what the path light does at a surface, because it seems like it should “kink”. We agreed that bending made it sound like it was “curving” the way a ruler bends when you grab its end up pull, which would violate our rule that light travels straight.
  • Some groups have suggested that there must be two different kinds of bounces. One bounce that allows images or reflections to be seen (like in mirrors), and another kind of bounce that allows objects to be seen (like grass).
  • Other groups have suggested that absorbing is when you see objects like a table, and bouncing is when you see light glaring off a surface or when you see a reflection.
  • We discussed how if you were outside tanning with tanning oil on, there might be three things happening with light. Some of the light is being absorbed, causing you to tan. Some of the light might bounce of the oil, causing a glare or reflection. And some of the light would be bouncing off your skin, allowing other people to see your skin.

(D) When light goes through a small hole, each path just keeps going straight through the hole

  • We decided that each piece of light doesn’t get “squished” through the hole, but rather all the light coming from different places get closer together as they move through the hole.
  • We struggled with what words to use… during discussion we sorted through the words “squish”, “close in”, “funnel”, “focus”, “cross”…  I still think we haven’t fully come to agreement, but I think we are leaning toward the idea that any given path of light either gets through or it doesn’t. If it gets through the hole, it just keeps continuing in its straight path. If it doesn’t get through, it’s because it hit the surface, which acts like a barrier to getting in the box. Many paths get through, and those that do just happen to get close together. They are forced to cross, as they go through because of the angles involved.

We spent the end of class trying to apply our rules for light to a novel situation they had not considered before: A long filament bulb through a small triangular hole, and what would change on the screen as we began covering up the more and more of the long filament bulb (from top down) until the just the very bottom of the long filament bulb was still left uncovered.

 

 

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