Physics · Practical apparatus

Convex mirror with converging lens

Use a convex lens to create a converging beam aimed at a point behind the convex mirror. Adjust mirror position until that point matches its centre of curvature. Normal incidence on the sphere makes rays retrace.

Open the interactive experiment →

Convex mirror with converging lens

குவி லென்சின் குவியும் கதிர்களை குவி ஆடியின் வளைவு மையத்தை நோக்கி அமைத்து ஒத்துப்பார்க்கவும்.

Key notes, relationships and model limits

Key relationship

Lens q=fd/(d−f); centre condition q−P=R; convex mirror f=−R/2.

Practical tip

Common trap

The centre-coincidence estimate is not valid away from the retracing condition.

Model limits

Ideal lens converging to a point behind the convex mirror. The centre-coincidence condition causes retracing. Focal estimate is meaningful only when residual≈0 and the first image lies behind the mirror.

What you will learn

Infer convex-mirror radius using a known converging focus.

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

Lens f20,d30 gives I60 cm; mirror P40 and R20 gives coincidence and fmirror−10 cm.

Why this matters

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

Before you start

SI units · algebra · graph reading

Check your understanding

A spherical mirror focal-length magnitude is?

Its full radius
Half its radius
Twice its radius

Read the explanation

Paraxial f=R/2; convex sign is negative in the stated convention.

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