Question

With the help of a ray diagram, describe the construction and working of a compound microscope.

Hint:

Compound microscope facts:

Two convex lenses
Objective → real image
Eyepiece → virtual magnified image
Final image is inverted

Answer 1

Concept: A compound microscope is an optical instrument used to observe very small objects by producing highly magnified images using two convex lenses:

Objective lens
Eyepiece lens
Construction:

Consists of two coaxial convex lenses mounted at the ends of a tube.
Objective:

Short focal length
Small aperture
Placed close to the object

Eyepiece:

Relatively larger focal length than objective
Acts as a magnifying glass
Placed near the eye

The distance between lenses is adjustable (tube length).
Ray Diagram (Description):

Object placed just beyond focal point of objective.
Objective forms a real, inverted, enlarged intermediate image.
This image lies within the focal length of the eyepiece.
Eyepiece produces a virtual, magnified final image.
Working:
Step 1: Formation of intermediate image.

Object placed slightly beyond the focal length of objective.
Objective forms:

Real
Inverted
Magnified image inside the tube


Step 2: Final image formation.

Intermediate image acts as object for eyepiece.
Eyepiece acts as a simple magnifier.
Final image is:

Virtual
Highly magnified
Inverted relative to original object

Magnifying Power (optional formula): For final image at least distance of distinct vision \( D \): \[ M = \left(\frac{L}{f_o}\right)\left(1 + \frac{D}{f_e}\right) \] Where:

\( L \) = tube length
\( f_o \) = focal length of objective
\( f_e \) = focal length of eyepiece
Conclusion: A compound microscope achieves high magnification by:

Objective producing a real magnified intermediate image
Eyepiece further magnifying it as a virtual image