Magnification - JEE Important Topic

When the size of an object gets enlarged, the quantified parameter is known as ‘magnification’. When there is a reduction in the size of an object, this quantified parameter is known as ‘minification’ or ‘de-magnification’. The quantified parameter is known as the ‘magnification factor’. It acts as a scaling factor of the image. The devices which are used for the same purpose of an image are the microscope, magnifying lens, etc.

This article gives an overview of what is magnification, the magnification formula for the lens, types of magnification, magnification factor, and the S.I. unit of magnification. 

Magnification Formula

Magnification is defined as the ratio of the height of an image to the height of an object. In terms of the image and the object distance, magnification is defined as the ratio of an image distance to the object distance with a negative sign. Sometimes, it is also known as the ‘magnification factor’. Mathematically, the relationship is given as:

• In terms of the height of the image and object, the magnification formula is shown below: $m=\dfrac{h_i}{h_o}$

• In terms of image distance and object distance, the magnification formula is shown below: $m=-\dfrac{v}{u}$

Here, h_i = Height of an image, h_o = Height of an object

v = Image distance, u = Object distance and m= Magnification

The given magnification formula for lens and mirror is used for solving complex real-life-based numerical problems related to the concept of optics. 

What is the Unit of Magnification?

The S.I. unit of magnification is determined based on the magnification formula for lenses and mirrors. In both cases, magnification is determined based on a ratio of the same units, i.e. the ratio of image distance to the object distance and the ratio of the height of the image to the height of the object. That is why magnification has no dimension. It is a dimensionless parameter and has no units.

Types of Magnification Lenses

The types of magnification are decided based on the magnification lenses. There are two types of magnification which are given below:

• Simple lenses

• Compound lenses

1. Simple Lenses:

Simple lenses are lenses composed of a single lens and are used for magnifying the objects and things kept in front of the lens. These lenses are used for the study and in experimentation laboratories. The strength of the lens is measured by its power and its unit is a dioptre. 

The range of the magnification for the simple lens is from 2x (2 times) to 6x (6 times). It depicts that the size of the image will lie in the range of 2 times the size of an object (in case of lowest strength) to 6 times the size of an object (in case of highest strength). The only thing that matters is that simple lenses are not able to produce high-quality images.

For example, simple lenses are used in spectacles, magnifying glasses, magnifying lenses, etc.

2. Compound Lenses:

Compound lenses are those lenses that are composed of more than one single lens and are used for magnifying objects, things that are kept far from the lens. Compound lenses are made up of two thin lenses for magnifying the object. These compound lenses are used to magnify and obtain a clear image of the object. The strength of the lens is measured by its power and its unit is a dioptre.

The range of the magnification for the simple lens is from 4x (4 times) to 400x (400 times). It shows that the size of the image will lie in the range of 4 times the size of an object (in case of lowest strength) to 400 times the size of an object (in case of highest strength). These compound lenses have overcome the limitation of simple lenses, as it produces high-quality images, which are placed far away from the lens. For example, compound lenses are used in telescopes, compound microscopes, binoculars, etc.

Conclusion

This article concludes with brief information about one of the optical parameters i.e., magnification. It has also explained the strength of the lenses, types of magnification, magnification factor, etc. This article also clears queries like what is magnification, the S.I. unit of magnification and also derives the relationship of the magnification formula for lenses and mirrors.