Precautions taken in experiments about formation of images by a lens?

• A. Use a darkened area
• B. Object and lens same height on bench
• C. Avoiding parallax error in measurement, and look perpendicular to the ruler.
• D. Object/lens/screen perpendicular to bench

Answer: (C)

When studying how lenses form images, getting measurements right is essential. The position and size of the image are read from scales on rulers, so any mistake in reading the scale can lead to incorrect values for image distance, magnification, or focal length. Parallax error happens when you look at a scale from an angle rather than straight on—the measurement you estimate shifts with your viewpoint. Looking perpendicular to the ruler removes this error because you’re reading the true value at eye level. That direct, perpendicularly viewed measurement is the most reliable precaution for accurate results in lens-image experiments.

Other options don’t address measurement accuracy as directly. A darkened area might help in some setups but isn’t fundamental to preventing reading errors. Keeping the object and lens at the same height helps alignment, but it doesn’t tackle the core issue of reading measurements accurately. Perpendicular alignment of everything to the bench is good practice, but the key precision step is reading the scale without parallax.