Focal length of concave lens experiment

[ash_nar]

Is there any way to find rough focal length of concave lens and convex mirror without using convex lens? Though I did the experiments(with object and image needles, not candle) very carefully with no parallax errors during my practical class, my readings are incorrect. I want to know if der s way to find out rough focal lengths of diverging lens n mirror in a simple way so that I can manipulate my readings accordingly during practical exam... Plzzzzzz help...

 

[Andy Resnick]

One easy way to get a rough estimate is to use either the sun or an overhead light as the source- the souce is then approximately at infinity. For a convex lens, the measurement is the straightforward- the distance from the lens to the focused spot is the focal length. For a concave lens, it's a little more difficult because the image is virtual. However, by making two measurements at different distances from the lens to calculate the divergence, you could calculate where the virtual spot is by geometry.

At least that's what I would do for a first approximation.

 

[astrokreng]

Yes, there are ways to find the rough focal length of a concave lens and convex mirror without using a convex lens. One method is to use the thin lens formula, which states that the focal length (f) of a lens is equal to the product of the object distance (u) and image distance (v) divided by the sum of the object and image distances (u+v). By measuring the object and image distances and plugging them into the formula, you can calculate the rough focal length of the lens or mirror.

Another method is to use the lens/mirror equation, which states that the inverse of the focal length (1/f) is equal to the sum of the inverse of the object distance (1/u) and the inverse of the image distance (1/v). By rearranging the equation and solving for f, you can again find the rough focal length of the lens or mirror.

It is important to note that these methods will only give you a rough estimate of the focal length, as they do not take into account any errors or imperfections in the lens or mirror. To get a more accurate measurement, it is recommended to use a convex lens or other specialized equipment.

If your readings were incorrect during your practical class, it is possible that there were other factors at play, such as incorrect measurements or experimental errors. It is important to carefully follow the instructions and guidelines for the experiment and to double-check your measurements to ensure accuracy.

In terms of manipulating your readings during a practical exam, it is important to understand the principles and equations involved in finding the focal length of a lens or mirror. This will allow you to make any necessary adjustments or corrections to your readings and calculations.

Overall, it is always best to consult with your instructor or a more experienced scientist for assistance and guidance in conducting experiments and interpreting results. Good luck with your practical exam!