Draw a labelled ray diagram showing the formation of image in a compound microscope. Define its magnifying power and write expression for it.

**OR**

Using Huygen's construction, explain reflection of a plane wave by a plane surface.

Question

Draw a labelled ray diagram showing the formation of image in a compound microscope. Define its magnifying power and write expression for it.

**OR**

Using Huygen's construction, explain reflection of a plane wave by a plane surface.

Accepted Answer

![Figure — Answer takes the compound-microscope alternative and the stem says 'Draw a labelled ray diagram ... compound m](/figures/ray-optics-and-optical-instruments/ray-formation-image-compound-microscope-fig-9-24.svg)

>

> [!TLDR]
> In a compound microscope, the objective forms a real magnified image, which the eyepiece magnifies further as a simple magnifier; overall magnifying power $m = m_o 	imes m_e$.
>
> **Ray diagram (described):** The object $O$ is placed just outside the focus $F_o$ of the objective lens (a short focal-length convex lens). The objective forms a real, inverted, and magnified image $I_1$ inside the microscope tube, beyond its own focal length but within the focal length of the eyepiece. This intermediate image $I_1$ acts as the object for the eyepiece (a convex lens used as a simple magnifier), which forms a final image $I_2$ — virtual, further magnified, and inverted relative to the original object — typically at the near point (least distance of distinct vision) $D$, or at infinity for relaxed-eye viewing. Rays from the top of the object pass through the objective converging to the top of $I_1$, then diverge from $I_1$ through the eyepiece to form the enlarged virtual image $I_2$.
>
> **Magnifying power:** Defined as the ratio of the angle subtended at the eye by the final image to the angle subtended by the object when placed at the near point (viewed directly, without the instrument).
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> The overall magnifying power is the product of the objective's linear magnification $m_o$ and the eyepiece's angular magnification $m_e$ (acting as a simple magnifier):
> $$m = m_o 	imes m_e$$
>
> For the final image formed at the near point $D$:
> $$m = \dfrac{v_o}{u_o}\left(1+\dfrac{D}{f_e}ight)$$ …

Q.Draw a labelled ray diagram showing the formation of image in a compound microscope. Define its magnifying power and write expression for it. OR Using Huygen's construction, explain reflection of a plane wave by a plane surface.

Concept understanding — Microscope Magnification

Microscope Magnification

How the two lenses work together

The objective's magnification

The eyepiece's magnification

Total magnifying power

Worked example

Why this formula?

Microscope Magnification: Why the Formula Holds

1. What Does "Magnification" Mean in a Microscope?

2. The Key Formula

3. Derivation of Objective Magnification $M_o$

Step 1: How the objective works

Step 2: Using the lens formula

Step 3: The tube length approximation

Step 4: Magnification formula

4. Derivation of Eyepiece Magnification $M_e$

Step 1: The eyepiece as a simple magnifier

Step 2: Angular magnification

Q.Draw a labelled ray diagram showing the formation of image in a compound microscope. Define its magnifying power and write expression for it. OR Using Huygen's construction, explain reflection of a plane wave by a plane surface.

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