In a lens formation experiment, why should the object and lens be at the same height on the bench?

• A. To ensure measurements are consistent
• B. To prevent parallax error
• C. To keep the lens from overheating
• D. To align with ruler marks

Answer: (A)

The main idea being tested is making measurements reliable and comparable. In a lens formation setup you measure distances along the bench (object to lens, lens to screen or image). If the object and lens sit at the same height, those distances are read along the same straight line, so the readings reflect the actual horizontal separations along the optical axis. This keeps object distance and image distance consistent from trial to trial, which is essential for accurately applying equations like 1/f = 1/v + 1/u.

If the heights were different, readings could vary because you’d be judging distances from slightly angled viewpoints or along a slanted line, introducing systematic errors. Parallax can contribute in that situation too, but the core benefit of equal height is ensuring the measurements themselves are consistent and reproducible.