Physics · Practical apparatus

Liquid lens with plane mirror

Find the no-parallax needle distance in air and with the liquid layer. The liquid layer has negative power in this geometry. The focal change and known curvature give the liquid index.

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Liquid lens with plane mirror

காற்றிலும் திரவம் சேர்த்த நிலையிலும் ஒத்துப்படும் ஊசி தொலைவைத் தேடவும். குவிய மாற்றத்திலிருந்து திரவத்தின் n கிடைக்கும்.

Key notes, relationships and model limits

Key relationship

1/F=1/fair−(nliquid−1)/R; nliquid=1+R(1/fair−1/F).

Practical tip

Find the no-parallax needle distance in air and with the liquid layer. The liquid layer has negative power in this geometry. The focal change and known curvature give the liquid index.

Common trap

The formula depends on the stated liquid-layer shape and curvature sign.

Model limits

Thin convex lens with a plano-concave liquid lens against an adjacent plane mirror; known curvature. Negative or infinite combined focal length cannot give the positive-needle coincidence shown.

What you will learn

Infer liquid index through an autocollimation focal change.

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

fair20 cm,R30 cm,n1.5 gives combined F30 cm.

Why this matters

The model connects liquid lens with plane mirror with an observable reading. Check the equation and assumptions before applying it.

Before you start

SI units · algebra · graph reading

Check your understanding

The plano-concave liquid layer in this setup contributes?

Always positive power
Negative power
No optical effect

Read the explanation

Its curved interface produces diverging power relative to the stated thin-lens geometry.

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