Name: Angular Magnification and Magnifying Power
Uploaded: 2019-07-19
Duration: 7 min 43 s
Description: Angular magnification can be used to assess the size of the object as it appears to the eye. To learn more about angular magnification produced by an optical...

Question

Draw ray diagram of compound microscope. Write its magnifying power in normal adjustment. If objective and eye-piece are interchanged, will it behave like a telescope? Explain.

Accepted Answer

A microscope is an optical instrument which forms large image of a close and minute object. This image subtends a large visual angle at the eye so that the object looks large.

In the simplest form, a simple microscope, or magnifying glass is just a thin, short-focus convex lens carrying a handle. The object to be seen is placed between the lens and its focus and the eye is placed just behind the lens. Then, the eye sees a magnified, erect and virtual image on the same side as the object. The position of the object between the lens and its focus is so adjusted that the image is formed at the least distance of distinct vision from the eye. The image is then seen most distinctly.

The magnifying power of compound microscope is,

$M = \frac{β}{\propto} . . . . . (i)$ , where,

$β =$ Visual angle made by the image and

$\propto =$ Visual angle made by the object.

Since angles are very small,

$M = \frac{\tan β}{\tan \propto} . . . . . . (ii)$ or

$M = \frac{A'' B''}{A' B'} \times \frac{A' B'}{AB} = m_{e} \times m_{o} . . . . . (iii)$ or

Now using lens formula for objective lens,

$m_{o} = \frac{f_{o}}{u_{o} - f_{o}}$ and

Now using lens formula for eye piece,

$m_{e} = \frac{v_{e}}{u_{e}}$

Since the image is forming at least distance of distinct vision,

$m_{e} = \frac{D}{u_{e}}$

Thus, equation $(iii)$ becomes,

$M = \frac{f_{o}}{u_{o} - f_{o}} (\frac{D}{u_{e}}) . . . . . (iv)$

For significant magnification, the objective of compound microscope is of very small aperture.

If the objective and eye-piece are interchanged, it will not behave like a telescope.

Draw ray diagram of compound microscope. Write its magnifying power in normal adjustment. If objective and eye-piece are interchanged, will it behave like a telescope? Explain.

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