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Light Ray Path

  • Thread starter Air
  • Start date
  • #1
Air
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Homework Statement


The diagrams below illustrate the formation of a rainbow. Figure 1 shows the general arrangement and Figure 2 shows the path of a ray through a raindrop with the centre of the raindrop is labelled O.

Figure 1:
Raindrop1.jpg


Figure 2:
Raindrop2.jpg


a.)
Where the ray enters the raindrop in Figure 2, mark the angle of incidence i and the angle of refraction, r.

b.)
Figure 2 is drawn to scale. By taking suitable measurements, show that the refractive index of water is about 1.3.


Homework Equations


[itex]\mu = \frac{\sin i}{\sin r}[/itex]


The Attempt at a Solution


a.)
Raindrop2Attempt.jpg

^ Have I labelled it correct?

b.)
I measured the angle that I have labelled above and got [itex]i = 25^\circ[/itex] and [itex]r = 35^\circ[/itex] and this gives [itex]\mu = 0.74[/itex]. This is incorrect. The correct answer is [itex]i = 53, \ r = 39, \ \implies \mu = 1.27[/itex]. Where have I gone wrong here?
 

Answers and Replies

  • #2
Redbelly98
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The normal should be perpendicular to the water's surface.
 
  • #3
Air
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So, is it like this?

Raindrop2Attempt2.jpg
 
  • #4
Air
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Or, is it like this? :confused:

Raindrop2Attempt3.jpg
 
  • #5
555
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You just seem to be drawing random lines lol...

The normal line on a spherical surface at some point P is always the line that goes from P through the center of the circle.

In other words; if you draw a straight line through the center of a circle, then at the points where it intersects the circle the angle between the line and the circle (at that point) is exactly 90 degrees, or perpendicular.
 
  • #6
Air
202
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You just seem to be drawing random lines lol...

The normal line on a spherical surface at some point P is always the line that goes from P through the center of the circle.

In other words; if you draw a straight line through the center of a circle, then at the points where it intersects the circle the angle between the line and the circle (at that point) is exactly 90 degrees, or perpendicular.
Oooh, I understand now. I guess it is this:

Raindrop2Attempt4.jpg


Am I correct?
 
Last edited:
  • #7
Redbelly98
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Yes, that looks good.
 

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