Lens Formula for Real Image Formation

Steps:

• Note the image position from the diagram, giving image distance v (positive for real image on opposite side of lens).
• Apply the thin lens formula: 1/f = 1/v + 1/u, where u is object distance (negative in sign convention for object on incident side).
• Solve for u: u = (v f)/(v - f), ensuring u < -f for real image.
• Match calculated |u| to choice positions relative to f (e.g., beyond 2f, between f and 2f).

Why A is correct:

• A places object beyond 2f, yielding real image at shown v > 2f via lens formula, as 1/|u| < 1/(2f) produces v > 2f.

Why the others are wrong:

• B (at 2f) produces real image at 2f, not the shown position beyond 2f.
• C (between f and 2f) produces real image between 2f and infinity, but not exactly at shown v.
• D (at f) produces image at infinity, not the finite shown position.

Final answer: A