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(i) With the help of a ray… (Class 12 Physics 2026, Q33b)

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PhysicsCBSE Class 12 · Board exam 2026, set 55/5/1 · 5 marks · Long answer

CBSE Class 12 Physics 2026: question 33(b)

Set in the CBSE Class 12 board exam of 2026, paper 55/5/1, section E, question 33(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q33(b) · 5 marks · Long answerRay Optics and Optical Instruments

(i) With the help of a ray diagram, describe the construction and working of a compound microscope.
(ii) (I) The real image of an object placed between f and 2f from a convex lens can be seen on a screen placed at the image location. If the screen is removed, is the image still there ? Explain.
(II) Plane and convex mirrors produce virtual images of objects. Can they produce real images under some circumstances ? Explain.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Think of the microscope as two magnifying stages: the objective first, then the eyepiece acting as a simple magnifier.

Hint 2

Where should the intermediate image lie relative to the eyepiece focus so that the final image is virtual and enlarged?

Hint 3

For part (ii), ask what a real image physically is, and what happens if the incident rays are already converging before they reach the mirror.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) Ray diagram (described). Two coaxial convex lenses are drawn: a small objective O and a larger eyepiece E.

    • Object AB is placed just beyond the focus of the objective.
    • Rays from B through the objective form a real, inverted, magnified image A′B′. This image lies between E and its focus .
    • Rays from B′ through the eyepiece diverge.
    • When produced backwards, these rays meet at B″, forming the final virtual, inverted, highly magnified image A″B″ at the near point (distance D).
    1 mark

  2. Construction. The microscope has two convex lenses mounted coaxially in a tube:

    • The objective has a small focal length and a small aperture.
    • The eyepiece has a somewhat larger focal length and a larger aperture.
    • The separation between them can be adjusted.
    1 mark

  3. Working.

    • The objective forms a real, inverted, magnified image of the object, with .
    • The eyepiece then acts as a simple magnifier, giving when the final image is at the near point.
    • The total magnification is .
    • For the final image at infinity, , where is the tube length.
    1 mark

  4. (ii)(I) Yes, the image is still there. A real image is the point where the refracted rays actually meet. These rays keep travelling and diverge beyond that point. An eye placed beyond the image position, in the path of these diverging rays, sees the image in space. The screen only scatters the light so that the image is visible from all directions.

    1 mark

  5. (ii)(II) Yes, provided the light falling on the mirror is converging, i.e. the object is virtual (behind the mirror).

    • Plane mirror: rays converging towards a point behind it reflect and converge to a point in front of it, forming a real image.
    • Convex mirror: a real image forms if the virtual object lies between its pole and focus.
    1 mark

Answer: (i) Objective forms a real, magnified image within the focus of the eyepiece; eyepiece forms the final virtual magnified image; . (ii)(I) Yes, the rays still converge there and can be seen by an eye beyond it. (II) Yes, when a converging beam (virtual object) falls on them.

Where the marks are

  • Correct labelled ray diagram of a compound microscope (1 mark)
  • Construction: objective of small focal length and aperture, eyepiece of larger focal length (1 mark)
  • Working: real image by objective, virtual final image by eyepiece, magnification expression (1 mark)
  • Image still exists, since the rays actually converge there and diverge beyond it (1 mark)
  • Real image possible for plane/convex mirrors with a converging incident beam (virtual object) (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Ray Optics and Optical Instruments, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 55/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.