Name: Telescope
Uploaded: 2019-07-19
Duration: 7 min 39 s
Description: How do you see the details of distant objects? Do you want to learn an amazing optical instrument used to see distant objects' details? Watch this video.

Question

Draw a neat labelled ray diagram showing the formation of an image at the least distance of distinct vision

D

by a simple microscope. When the final image is at

D

, derive an expression for its magnifying power at

D

.

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.

Magnifying power of simple microscope,

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

$β =$ Visual angle made by the image and

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

Since, these angles are very small,

Thus, $M = \frac{\tan β}{\tan \propto} = \frac{A' B'}{D} \times \frac{D}{A B} = \frac{A' B'}{A B} = \frac{v}{u} ‐ equation (ii)$

Applying lens equation, $\frac{1}{v} - \frac{1}{u} = \frac{1}{f}$

Multiplying both sides with $v$ , we have

$\frac{v}{v} - \frac{v}{u} = \frac{v}{f}$

or, $1 - M = \frac{v}{f}$

But, $v = - D$

So, the above equation becomes

$M = 1 + \frac{D}{f}$ .

This gives the expression for the magnifying power of a simple microscope.

Draw a neat labelled ray diagram showing the formation of an image at the least distance of distinct vision $D$ by a simple microscope. When the final image is at $D$ , derive an expression for its magnifying power at $D$ .

Important Questions on Optical Instruments

Learn and Prepare for any exam you want !

Draw a neat labelled ray diagram showing the formation of an image at the least distance of distinct vision D by a simple microscope. When the final image is at D, derive an expression for its magnifying power at D.

Important Questions on Optical Instruments

Learn and Prepare for any exam you want !

Draw a neat labelled ray diagram showing the formation of an image at the least distance of distinct vision $D$ by a simple microscope. When the final image is at $D$ , derive an expression for its magnifying power at $D$ .