Optical Instruments - Compound Microscope - 2

We all seen the Microscope in our school laboratory.

It is a device that we used to see Onion tissue in a school.

These instruments also made it possible to see the germs in our hands.

But, a simple microscope just has a magnification limited to $40X$, it's difficult to see tissue with the help of this.

So, we used a Compound microscope for this purpose.

It has a magnification up to the range of $1000X$.

Now, we will learn about the Compound Microscope.

Let's learn about a Compound microscope.

To magnify beyond $40X$, we add a second lens in the simple microscope. This is called Compound Microscope.

There two types of lenses are present in a compound microscope: Objective lens and Eyepiece lens.

The lens through which the final image is observed, called the eyepiece lens.

Whereas the lens just above the object is called the objective lens.

Suppose there are two lenses $L_1$, objective lens and $L_2$, eyepiece lens

The object $AB$ is placed beyond the focus $F_1$ of the objective lens.

The objective lens forms a real, magnified and inverted image $A_1{B}_1$.

This image $A_1{B}_1$ will become the object for the eyepiece lens.

And the distance between the two lenses is adjusted such that image $A_1{B}_1$ lies within the focus of the eyepiece lens.

The eyepiece forms a magnified, virtual and inverted image as compared to the original object.

These two lenses together produce a highly magnified, virtual and inverted image of an object.

Now, let's find the magnifying power of this microscope.

The formula for magnifying power (M) of this microscope is,

We can find the value of $\beta$ using a ray-diagram.

And the value of $\alpha$ will be as above.

Now, to calculate the magnifying power, we can write as above.

We know the value of $A_1{B}_1$ and $AB$.

So, we can write the Magnification (M) as above.

Now, let's apply the lens formula on the eyepiece lens.

Therefore, the formula will become as above.

By putting the value of $\frac{1}{u_e}$, we get the value of magnification (M).

Now, when the final image is formed at $D$ i.e. $v=D$.

Now, let's find the Magnification when an image is formed at infinity, i.e. $v_e=\infty$.

So, the value of magnification when the image is formed at infinity.

This is all about the compound microscope.

Revision

A compound microscope has two lenses objective lens and eyepiece lens.

The magnification power of Compound microscope is as above.

The magnification power of a Compound microscope when an image is formed at a distance $D$.

The magnification power of a Compound microscope when an image is formed at infinity.

The End