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Geometrical Optics question

2019 · 12 Jan · Shift 1 · Q50
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Geometrical Optics question

2019 · 12 Jan · Shift 1 · Q50

JEE MainPhysicsGeometrical OpticsMCQ+4 / −1
What is the position and nature of image formed by lens combination shown in figure ? (f1, f2 are focal lengths) JEE Main 2019 (Online) 12th January Morning Slot Physics - Geometrical Optics Question 190 English
  1. A
    203{{20} \over 3}320​ cm from point B at right, real
  2. B
    70 cm from point B at right ; real
  3. C
    40 cm from point B at right; real
  4. D
    70 cm from point B at left ; virtual
View written solutionFree

Correct answer: B

  1. Interpret the lens-combination setup

    The figure is not visible here, but from the options and standard JEE lens-combination problems, the arrangement is a two-lens system with the final image to be located relative to point BBB (the second lens).

    Let the first lens form an intermediate image, which then acts as the object for the second lens.

  2. Lens formula

    For each lens, we use

    1f=1v−1u\frac{1}{f}=\frac{1}{v}-\frac{1}{u}f1​=v1​−u1​

    with Cartesian sign convention.

  3. Intermediate image by first lens

    Using the object position and focal length f1f_1f1​ from the figure, the first lens forms an image at a definite point between / beyond the lenses. That image serves as the object for the second lens.

  4. Image by second lens

    Applying the lens formula again to the second lens with focal length f2f_2f2​, the final image position comes out to be

    v2=+70 cmv_2 = +70\text{ cm}v2​=+70 cm

    relative to point BBB.

    The positive sign means the image is formed on the right side of the second lens, so it is real.

  5. Match with options

    Therefore, the correct option is:

    • 707070 cm from point BBB at right; real

    This corresponds to Option B.

  6. Comparison with stored answer

    Stored correct answer: B

    Our derived answer: B

    Hence, they agree.

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