Significant figures in microscope field of view area calculation

Steps:

• Calibrate eyepiece graticule against stage micrometer: each 0.1 mm division corresponds to a measured number of graticule units, giving scale factor with 3 significant figures (e.g., diameter ≈ 1.25 mm or 1250 μm).
• Determine radius r from half the calibrated diameter, preserving 3 significant figures.
• Compute area = π r² with π = 3.142 (4 significant figures); result has 3 significant figures due to limiting measurement precision.
• Convert to μm² if needed (1 mm = 1000 μm, exact) and round to 3 significant figures: 491 μm².

Why D is correct:

• 491 has 3 significant figures, matching the precision of 0.1 mm divisions (2–3 figures) limited by calibration accuracy.

Why the others are wrong:

• A: 2 significant figures and incorrect magnitude/units (too small for typical field).
• B: Only 2 significant figures; incomplete (missing m value).
• C: 3 significant figures but incorrect scientific notation (missing exponent) and wrong magnitude.

Final answer: D