Physics · Class 12

Microscope and telescope

An objective and an eyepiece perform different jobs. The telescope compares angular sizes of distant objects. A microscope uses a real intermediate image before the eyepiece magnifies it.

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Microscope and telescope

பொருளருகு லென்சும் கண் அருகு லென்சும் வேறு பணிகளைச் செய்கின்றன. தொலைநோக்கியும் நுண்ணோக்கியும் கோணப் பெருக்கத்தை வழங்குகின்றன.

Key notes, relationships and model limits

Key relationship

Telescope relaxed M=−fo/fe; near-point M=−(fo/fe)(1+fe/D), length=fo+feD/(D+fe). Microscope |M|≈(L/fo)(D/fe), or (L/fo)(1+D/fe) at near point.

Remember

An objective and an eyepiece perform different jobs. The telescope compares angular sizes of distant objects. A microscope uses a real intermediate image before the eyepiece magnifies it.

Common trap

A telescope’s angular magnification is not a linear image-height ratio.

Model limits

This panel models a two-lens refracting telescope and an approximate compound microscope. It does not supply a reflecting-telescope optical train.

What you will learn

Relate objective and eyepiece focal lengths to magnifying power.

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

The relaxed telescope length is110 cm; microscope L20,fo2,fe5,D25 gives |M|≈50.

Why this matters

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

Before you start

SI units · algebra · graph reading

Check your understanding

For telescope fo=100 cm and fe=10 cm, |M| is?

Read the explanation

Angular magnification magnitude is fo/fe.

Course connection: Class XII Chapter 9. Consult the roadmap for CBSE, NEET, JEE Main and Advanced scope.