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Table of object and image distances for a convex lens

The same question, asked 3 times: 2024*, 2025*, 2026. Every wording below, oldest first.

Try each one first, then open its answer.

  1. Question 1

    2024

    36 (a)
    The variation of image distance (v) with object distance (u) for a convex lens is given in the following observation table. Analyse it and answer the questions that follow :
    S. No.Object distance (u) cmImage distance (v) cm
    1−150-150+30+30
    2−75-75+37⋅5+37{\cdot}5
    3−50-50+50+50
    4−37⋅5-37{\cdot}5+75+75
    5−30-30+150+150
    6−15-15+37⋅5+37{\cdot}5
    (i) Without calculation, find the focal length of the convex lens. Justify your answer. (ii) Which observation is not correct ? Why ? Draw ray diagram to find the position of the image formed for this position of the object. (iii) Find the approximate value of magnification for u=−30u = -30 cm.

  2. Question 2

    2025

    31
    A student placed a candle flame at different distances from a convex lens and focused its image on a screen. He recorded his observation in tabular form as given below :
    S.No.Distance of flame from the lens (cm)Distance of the image from the lens
    1−90-90+18+18
    2−60-60+20+20
    3−40-40+24+24
    4−30-30+30+30
    5−24-24+40+40
    6−20-20+60+60
    7−18-18+90+90
    8−12-12+120+120
    Analyse the observation table and on the basis of your analysis only, answer the following questions (without doing any calculations) : (a) What is the focal length of the convex lens used ? Give reason to justify your answer. (b) Which one of the sets of observations is not correct and why ? (c) Draw ray diagram to show image formation for any correct set of observation.

  3. Question 3

    2025

    36 (b)
    Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :
    Observation NumberObject distance (u) in cmImage distance (v) in cm
    1−15-15−60-60
    2−25-25+100+100
    3−30-30+60+60
    4−40-40+40+40
    5−60-60+30+30
    6−100-100+25+25
    (a) Determine the focal length of the lens. Give reason for your answer. (b) Find magnification of the image formed in Observation No. 3. (c) The numerical value of magnifications in cases of observation 1 and 2 is same. List two differences in the images formed in these two cases.

  4. Question 4 (case study, 4 parts)

    2026

    The variation of image distance (v)(v) with the object distance (u)(u) for a convex lens is given in the following observation table. Analyse it and answer the questions given below :
    S.No.Object distance (u)(u) cmImage distance (v)(v) cm
    1−150-150+30+30
    2−75-75+37⋅5+37{\cdot}5
    3−50-50+50+50
    4−37⋅5-37{\cdot}5+75+75
    5−30-30+150+150
    6−15-15+37⋅5+37{\cdot}5
    38 (a)
    Without calculation, find out the focal length of the given convex lens. Justify your answer.
    38 (b)
    Which one of the observations given in the table is not correct and why ?
    38 (c) (i)
    Find out the value of magnification for u=−30u = -30 cm. Write the nature of the image formed. Give reason for your answer.
    38 (c) (ii)
    Analyse the data given in the table above and draw the labelled ray diagram for u=−30u = -30 cm and v=150v = 150 cm.