Refraction - what's happening for real

  • Context: High School 
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    Refraction
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Discussion Overview

The discussion centers around the phenomenon of refraction, particularly how light behaves when transitioning between air and water. Participants explore the apparent bending of objects, such as a pole in water, and how this relates to established principles like Snell's law. The conversation includes personal experiences and attempts to reconcile textbook explanations with real-world observations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants express confusion about the apparent bending of a pole in water, noting that textbooks indicate light bends down when entering water, while their observations suggest the pole appears to bend up.
  • One participant explains that the bending of light can be understood through ray diagrams, indicating that light exiting water bends away from the normal, leading to a misperception of the pole's position.
  • Another participant reiterates that both the bending of light and the apparent position of the pole can be explained by Snell's law, suggesting consistency in the observations.
  • There is a suggestion that the apparent upward bending of the pole is due to the brain's assumption that light travels in a straight line, which can lead to misunderstandings about the actual position of the pole.
  • One participant shares their struggle with understanding the concept and expresses a desire to grasp it better, indicating that it is a challenging topic for them.

Areas of Agreement / Disagreement

Participants generally express confusion and seek clarification, indicating that multiple interpretations of the phenomenon exist. There is no consensus on the best way to understand the apparent bending of the pole, and the discussion remains unresolved with differing perspectives on the explanation.

Contextual Notes

Participants reference Snell's law and ray diagrams, but there are indications of missing assumptions and varying interpretations of how light behaves at the interface of different media. The discussion reflects a range of understanding and comfort with the topic.

Bunnyhop
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Ok. I don't understand this refraction stuff. The books all show the light bends down when light from the air enters water ah, change in medium. But when I clean our pool the rod appears to bend up. My Dad is a jock and he says to hunt for fish you throw the spear in front of the fish you see in the water. So what gives here. Doesn't make sense to me that the pole appears to bend up when the books say the light bends down! Confused.
 
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Doesn't make sense to me that the pole appears to bend up when the books say the light bends down! Confused.

Actually those two things are completely consistent. It's best understood by drawing a simple ray diagram. Imagine the path that a ray of light scattered from the tip of the pole will reach your eye. As the ray exits the water it will bend away from the normal and travel toward your eye at a "lower" angle as compared with the angle that it would approach your eye if the light traveled in a straight line. This fools your brain into thinking that the tip of the pole is further forward and at a shallower depth than it really is (hence the pole appears to bend upwards.)

BTW. You'll probably need to try and draw the ray diagram for yourself to really understand what I'm saying. I don't have time to post an image right now.
 
Bunnyhop said:
Ok. I don't understand this refraction stuff. The books all show the light bends down when light from the air enters water ah, change in medium. But when I clean our pool the rod appears to bend up.

The appearance of the rod is due to light from the pole in the water to the air and finally to your eye, which is the opposite direction of travel from what you describe in your second sentence.

Both are described by Snell's law, as uart says.
 
Thanks, I just found a drawing on Wilki, which I'm looking at, I think its what you are saying. Still seems confusing, though. It seems to me the pole appears to be bending up because the light is bedning up rather than down as the books seem to show. Am I a dumb nerd or what? LOL
 
Thanks, I'll look at Snell's law too.
 
No it looks like this. The light bends "downward" as you described, but the apparent position of the tip of the pole appears to be higher than it's actual position making the pole appear to bend upward. The reason for this "apparent" posiiton is that your brain assumes that the light travels in a straight line and therefore assumes that the tip of the pole lies in the direction that the light from that tip is entering the eye. The solid lines shows the actual pole and light ray while the dotted lines show the apparent pole position and the apparent light ray (the one that you brain thinks it should be becuse it assumes a straight path).

http://img220.imageshack.us/img220/3506/refractioniy9.png
 
Last edited by a moderator:
uart Thanks, I'm starting to get it. Guess my brain works backwards. LOL That bit on Wilki on Snell's law with the expanding rings put me in a trance but it finally started to make sense too. This concept is a hard one for me to get my hands around, right now I just want to choke it.
 

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