How Does Light Behave When Emitted From a Focal Point Through a Convex Lens?

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SUMMARY

The discussion centers on the behavior of light emitted from a bulb placed at the focal point of a convex lens. When light rays emanate from the bulb, they travel in various directions and pass through the lens, converging on the optical axis. The rays that are parallel to the optical axis after passing through the lens will converge at the focal point on the opposite side. This principle is crucial for understanding how convex lenses focus light, as demonstrated by the example of collecting sunlight to ignite paper.

PREREQUISITES
  • Understanding of convex lens properties
  • Knowledge of optical axis and focal points
  • Basic principles of light ray behavior
  • Familiarity with ray diagrams in optics
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  • Study the principles of ray diagrams for convex lenses
  • Learn about the lens maker's equation for lens design
  • Explore applications of convex lenses in optical devices
  • Investigate the concept of light ray reversibility in optics
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Students studying optics, physics educators, and anyone interested in the practical applications of convex lenses in focusing light.

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Homework Statement


1. A small bulb is placed in front of a convex lens. It is placed at one focal point of the lens. Draw at least five rays from the bulb that pass through the lens.

Where is the lens located in this case? Explain. (Hint: How are the rays that have passed through the lens oriented? From where do these rays appear to have come?)


Homework Equations


none


The Attempt at a Solution


Sorry I can't show the picture but since the bulb is at the focal point, doesn't that mean it is right on the optical axis? I really don't know how to draw 5 rays from that.
 
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It's on the axis. The rays begin at the lamp and go in different directions.
 
Yes, the bulb is on the optical axis. So just draw a lens with its optical axis and focal points and put the bulb at one of them. Consider the bulb a point-like light source.

Remember that you can collect the sun rays with a convex lens, and ignite a piece of paper. The rays of sun come from so far that they are parallel. Rays incident parallel with the optical axis are collected in the focus at the other side of the lens. Draw 5 such rays.

You know that the direction of light rays is reversible. If you turn the direction of the sunrays over, they will follow the same path as they arrived, going back towards the sun.

Starting rays from the focus, in what direction will they go after crossing the lens?


ehild
 
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