Physics · Practical apparatus

Spherometer curvature

The three legs define an equilateral triangle and the central screw measures sagitta h. Correct the flat-plate zero before finding a spherical surface radius.

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Spherometer curvature

மூன்று கால்கள் சமபக்க முக்கோணம் அமைக்கும். மைய திருகின் உயரம் h மூலம் வளைவு ஆரம் பெறலாம்.

Key notes, relationships and model limits

Key relationship

R=l²/(6h)+h/2.

Practical tip

The three legs define an equilateral triangle and the central screw measures sagitta h. Correct the flat-plate zero before finding a spherical surface radius.

Common trap

Use the central screw’s height relative to the three-leg plane; a small height error can strongly change the curvature estimate.

Model limits

spherical radius from an equilateral-leg spherometer. Sagitta must be resolved above zero; radius formula is exact for this leg geometry.

What you will learn

Adjust spherometer curvature apparatus, observe its reading and derive the indicated physical quantity.

Try the experiment

Try both scenarios, change one control, and predict the result before checking the graph and readouts.

Think of it this way

Change one input while keeping the others fixed, as you would in a controlled experiment.

Worked example

With l=50 mm and h=1 mm, R=2500/6+0.5≈417.17 mm.

Why this matters

The model connects spherometer curvature with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

With leg spacing fixed, a smaller sagitta indicates?

A smaller radius and a more curved surface.
A larger radius and a flatter spherical surface.
An unchanged radius.

Read the explanation

A larger radius and a flatter spherical surface.

Course connection: Virtual apparatus preparation. Check exact board/exam membership in the syllabus sources. Physical practical work remains necessary.