Magnifying Glass

Our visual apparatus is naturally designed to detect objects only up to a size of certain dimension

We might have seen our grandpa peering through a glass to read something indistinct to the normal eye

Or a child looking through a glass to watch an ant crawling through a bush plant

That glass is nothing but the magnifying glass

As the name suggests, the magnifying glass is used to look at an object, that is small in size and easily not detectable

A magnifying glass is considered to be a simple microscope

A simple microscope is one that uses just one lens for magnification

The principle of the simple microscope generally states, when a tiny object is placed within its focus, a virtual, erect and magnified image is formed

Let us look at the ray diagram of the magnifying glass

Let us place the object (represented as an upright red arrow) in front of the glass and view it from the other end

The object is placed in such a way that it lies between the optical centre C and the focus F

When observed from the other end of the glass the image will be formed as a virtual, erect and magnified image

So basically the main utility of the magnifying glass is to enable us to see a tiny object with greater clarity

Let us learn the formula for measuring the power of the magnifying glass

There are two ways to determine the magnification $\bullet$ Linear Magnification $\bullet$ Angular Magnification

The Linear magnification is represented in the equation form as $m=1+\frac{D}{f}$

Where f is focus and D is the distance of the magnified image from the optical center

Usually, this D is the least distance of distinct vision of the eye

The angular magnification is the ratio of the visual angle subtended by the image seen through the glass to the visual angle subtended by the object

When placed at D and seen through the eye

We know D to be the least distance of distinct vision

The virtual image subtends a visual angle $\beta$ to the eye when seen through the magnifying glass

The object (say OP) forms a visual angle $\alpha$ when it is placed at the least distance of vision

So the angular magnification is $M=\frac{\beta }{\alpha }$

Let us list down some of the most common uses of magnifying glass

Magnifying glasses are normally used to read small letters

Magnifying glasses are extensively used by watchmakers

Magnifying glasses are also used in spectrometers in the lab

Revision

A magnifying glass is a simple microscope

When a tiny object is placed within its focus, a virtual, erect and magnified image is formed

The power of the magnifying glass is represented in the equation form as $m=1+\frac{D}{f}$ where f is focus and D is the distance of the magnified image from the optical centre

Magnifying glasses are generally used $\bullet$ To read small letters$\bullet$ By watchmakers$\bullet$ In a spectrometer

The End