Question

take 5 double convex lenses of different thickness.Hold a meter scale perpendicular to a wall and in contact with the lenses .Hold a lens vertically on the scale and moving it away from the wall form a clear , bright image of a distant object on the wall measure the distance between the image and the wall . This is called the approximate focal length of the lens .Similarly find the approximate focal length of all the five lenses . What relation do you find between the thickness of the lens and its focal length?
Lay down the scale on the table. At one end of the scale fix the lens of maximum focal length with the help of plasticine.Now holding a lens(out of the remaining 4) vertically on the scale move it away from the first lens and observe a distant object through this pair of lens.Stop moving the second lens at the position where the biggest image is seen.Fix this lens at this position with the help of plasticin. measure the distance between the two lenses. Is the distance approximately equal to the sum of the focal lengths of the two lenses? Repeat the experiment with the remaining three lenses. In which lens-pair arrangement do you see the brightest image?Is the separation between the lenses minimum in this arrangement ?
Interchanging the position of the two lenses observe the distant object again. Does its image still appear bigger ? Near the scale end lens place a small object and observe it through the pair of lenses . Does it appear bigger? List all your conclusions derived in this project.

Answer 1

Answer -

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• vertically on the scale move it away from the first lens and observe a distant object through this pair of lens.Stop moving the second lens at the position where the biggest image is seen.Fix this lens at this position with the help of plasticin. measure the distance between the two lenses. Is the distance approximately equal to the sum of the focal lengths of the two lenses.

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