you have a lens suggest an experiment to find out the focal length of the lens
Answers
Answer:
Put the lens parallel with a wall or white flat surface and focus distant light source (streetlam), horizon or lamp in your room on the wall until you get sharp image. The lamp must be near optical axis of the lens. a is distance to lamp, streetlamp, or horizon. a' is distance to wall. Calculate f from a and a'.
For more info about focal length see Focal length on Wikipedia
Answer:
Aim: To find the focal length of a lens
Apparatus required: double convex lens, metre scale, a white screen, lens holder ,distant object
Procedure:
• Set up the apparatus near a window so to locate a distant object .
• Mount the convex lens on the lens holder.
• Now place the metre scale on the table and keep the lens at a distance of 5 cm mark on the metre scale such that the mid point of lens holder coincides with 5 cm mark.
• Place the white screen behind the lens such that the image of the object is formed on the screen.
• Now move the screen until you get a sharp, diminished & inverted image of the distant object.
• Mark the point on the scale where you get the desired image. The difference between the lens mark & the screen mark will give the focal length.
• Now place the lens on a new position that is 10 cm and find the focal length.
• Repeat the above steps by keeping the lens at 10 cm, 15 cm & so on to get more observations