What is the Focal Length of a Convex Lens?

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Discussion Overview

The discussion revolves around determining the focal length of a convex lens using sunlight to project an image onto a wall. Participants explore the relationship between the image created and the focal point, as well as the application of the thin lens equation in this context.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant questions whether the image created by the sun is the focal point or merely the distance of the image, and how to incorporate this into the thin lens equation given the object's distance is considered infinite.
  • Another participant asserts that since the sun is far away, the distance measured from the lens to the sun's image is equivalent to the focal length.
  • A different participant expresses uncertainty, suggesting that the sun's image needs to be focused properly before measuring the distance between the projection and the lens.
  • One participant explains that convex lenses have a focal point in front of the lens and describes the conditions under which real and virtual images are formed, noting that the transition point between these images indicates the focal point.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the image created and the focal length, with some asserting that the distance to the image corresponds to the focal length, while others emphasize the need for proper focusing. The discussion remains unresolved regarding the precise method for determining the focal length in this scenario.

Contextual Notes

Participants do not clarify certain assumptions, such as the conditions under which the thin lens equation applies or the specifics of measuring distances in this context.

Yesofcourse
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I am trying to find the focal length of a convex lens, so i let the sun shine through my window to create an image on my wall. Is that image the focal point or is it just the distance of the image? And if it is the distance of the image, how do I put it into the thin lens equation, since the distance of the object is infinite?
 
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Since the sun is so far away, the distance you measure from the lens to the sun's image is equal to the focal length.
 
Im pretty sure the sun's image needs to be focused doe. I think. then you measure the distance between the projection and the lens.
 
Convex lenses have a focal point in front of the lens. If the distance from what you are focusing is shorter than the focal point, then you end up with a virtual image on the same side as you're object. If the distance is greater than the focal point, you end up with a real image that's projected upside down. Focusing the sun, you wouldn't notice the upside down aspect, so I would focus something not symmetrical, so you can tell. The point when the image changes from real to virtual is the focal point. Just move the lens back and forth until it changes.
 
thanks :D
 

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