In optics experiments we assume that the sun rays are parallel

In summary, the discrepancy between optics experiments and our everyday experience is due to perspective. When looking at things from a distance, the lines that are nearly parallel appear to meet at an angle, but when looking closer, they do not actually meet.
  • #1
ritwik06
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Even though in optics experiments we assume that the sun rays are parallel, we can clearly see that the sunlight seems to diverge from the sun when coming through the clouds. Whats the reason of this discrepancy?
 
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  • #2
Take a sheet of paper and draw two straight lines across it that are nearly parallel, but meet near one edge of the paper. Now hold the opposite edge of the paper near your eye, and tilt the paper so you're looking across the width of the paper towards the point where the lines meet. What does the angle between the lines look like now?

Or take a pair of chopsticks (or something similar), hold them together at one end with a small angle between them, and then look along the sticks from the "open" end. (Be careful not to poke your eyes out! :yuck: )
 
  • #3
jtbell said:
Take a sheet of paper and draw two straight lines across it that are nearly parallel, but meet near one edge of the paper. Now hold the opposite edge of the paper near your eye, and tilt the paper so you're looking across the width of the paper towards the point where the lines meet. What does the angle between the lines look like now?

Or take a pair of chopsticks (or something similar), hold them together at one end with a small angle between them, and then look along the sticks from the "open" end. (Be careful not to poke your eyes out! :yuck: )

Well, if the lines are nearly parallel how will they meet ? :eek:
 
  • #4
If the lines are exactly parallel, they never meet, of course. If they are not exactly parallel, that is, with a small angle between them, then they can meet.

Light rays from the sun are clearly not exactly parallel, because they do meet at the sun!

Have you tried my little experiment yet?

Also note that even lines that are exactly parallel can appear to meet "at infinity" because of geometric perspective effects. Have you ever looked down a long straight road or railroad track that extends to the horizon on a flat plain? The sides of the road or the rails of the track appear to meet at the horizon.
 
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  • #5
ritwik06 said:
Even though in optics experiments we assume that the sun rays are parallel, we can clearly see that the sunlight seems to diverge from the sun when coming through the clouds. Whats the reason of this discrepancy?

Perhaps you "clearly see that the sunlight seems to diverge" , I do not. What is this divergence you claim to observe. keep in mind that the angle at which the sun's rays come through the clouds is determined by the season and time of day, but that is not the same as divergence of the rays. I do not observe any divergence.
 
  • #6
Integral, ritwik is referring to something like this: http://www.vagabond-ireland.com/silver_lining.jpg [Broken]

The answer, ritwik, is in jtbell's post, and it's the same reason that railway tracks or the sides of a straight road appear to converge at a distant point (or diverge as they approach you) - perspective!

PS: For some reason, I missed the last part of jtb's second post, and the similarity of content is purely coincidental!
 
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  • #7
jtbell said:
If the lines are exactly parallel, they never meet, of course. If they are not exactly parallel, that is, with a small angle between them, then they can meet.

Light rays from the sun are clearly not exactly parallel, because they do meet at the sun!

Have you tried my little experiment yet?

Also note that even lines that are exactly parallel can appear to meet "at infinity" because of geometric perspective effects. Have you ever looked down a long straight road or railroad track that extends to the horizon on a flat plain? The sides of the road or the rails of the track appear to meet at the horizon.

Oh yes, I have understood now. I did the activity with the paper, now what should I do further?
 

1. What does it mean to assume that sun rays are parallel in optics experiments?

When we say that sun rays are parallel in optics experiments, it means that we are assuming that the light coming from the sun is traveling in straight lines that do not converge or diverge. This allows us to simplify the calculations and measurements in our experiments.

2. Why do we make this assumption in optics experiments?

This assumption is made because the sun is a very distant source of light, and its rays can be considered parallel for most practical purposes. It makes the experiments easier to understand and analyze, without significantly impacting the accuracy of our results.

3. Is this assumption always accurate?

No, this assumption is not always accurate. In reality, sun rays are not completely parallel, especially when considering the curvature of the Earth and atmospheric effects. However, for most optics experiments, the difference is negligible and does not significantly affect the results.

4. Are there any situations where this assumption is not valid?

Yes, there are some situations where this assumption is not valid. For example, when studying the behavior of light in curved mirrors or lenses, this assumption may not hold true. In these cases, we must consider the curvature of the surface and the convergence or divergence of light rays.

5. Are there any other assumptions made in optics experiments?

Yes, there are other assumptions made in optics experiments, such as the assumption that light travels in a straight line, and the assumption that the speed of light is constant. These assumptions allow us to simplify our experiments and make accurate predictions about the behavior of light.

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