Difference Between Mirror and Lens

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Lens and Mirror Difference

The lens is a transparent thick material (made of glass/plastic) that causes light rays to bend in a particular way as they pass through it, be it converging the rays to a specific point or diverging them away from the particular point.

A mirror is an object that helps us see our image and the image behind us.

So, what is the difference between lens and mirror? Let’s observe this by the images of these:

[Image will be Uploaded Soon]

Lens and mirrors have differences in their image formation. In this article, we will learn the lens and mirror difference.


Difference Between Lens and Mirror

Lens

Mirror

The lens is a material made of glass or plastic bounded by two surfaces. It can either be curved at one side or both sides. 

The mirror implies a glossy surface at one end and produces an image of an object by reflection. 

A mirror follows the laws of reflection.

The lens is a transparent thick material that is shaped in such a manner that it bends the light passing through it. 

It can converge the light rays onto a specific point or diverge it away from that point.

A mirror is a reflector that is shiny from one side and reflects the light rays coming from the object to make it appear as an image to the other side.

The lens is of two types viz: Concave lens and convex lens.

A mirror is of three types viz: concave mirror, plane mirror, and convex mirror

A lens has two focal points namely F and 2F.

A plane mirror has no focal point.

It forms an image the same size as that of the object.

A concave lens is a diverging lens

A convex lens is a converging lens.

A concave mirror is a converging mirror A convex mirror is a diverging mirror.

Concave lenses are used as an aid for people having Myopia or nearsightedness.

Convex lenses are used as an aid for people having Hypermetropia or farsightedness.

Examples of Concave mirror - shaving/make up mirror

In streetlights and car headlights

Convex mirror - Rearview mirror in two and three-wheelers

The formula for the image formation by the lens is:

\[\frac{1}{v}\] - \[\frac{1}{u}\] = \[\frac{1}{f}\]

Where,

v = the distance of the image

u = the distance of the object

f = focal length

The formula for the image formation by the mirror is:

\[\frac{1}{v}\] + \[\frac{1}{u}\] = \[\frac{1}{f}\]

Where,

v = the distance of the image

u = the distance of the object

f = focal length

Image formation for the object placed at infinity:

  1. Concave lens

  2. Convex lens

Sign conventions:

The ray diagram for the object placed at infinity:

  1. Concave mirror

  2. Convex mirror

Image formation for the object placed at F

  1. Concave lens

  2. Convex lens

Image formation for the object placed at F


Image formation for the object placed between F (focus) and O (optical center)

Image formation for the object placed between F and C

Real-life example:

Whatever we observe around us is because of something called ‘lens’. Eyes are natural lenses that help us to read, write, watch movies, distinguish among various shades of a single color.

Real-life example:

Mirrors help us see our image.

We use mirrors at beauty salons, on vehicle headlights, torchlights, streetlamps, 


Difference Between Mirror and Lens

The difference between mirror and lens can be better understood by their sign conventions followed by their varying image formation. Firstly, we will have a look at their sign conventions followed by the ray diagram of objects placed at varying positions in both the mirror and the lens.


Sign Convention of a Mirror:

  • All the distances should be measured from the pole (P) of the mirror. 

  • Distances that are measured in the direction of the incident rays should be considered positive, and negative when distances are taken from the opposite side of the incident rays.

  • If the image is formed behind the mirror, then the image distance is taken positively from the pole (P) along the principal axis.

  • The height of the object is taken as positive above the principal axis and negative along the principal axis.

  • The focal length ‘f’, is positive for a concave mirror and a convex mirror, it is negative.

Sign Convention of the Lens:

  • All the distances should be measured from the optical center of the lens.

  • Distances that are considered along with the direction of the incident rays should be considered positive, and negative when distances are taken from the opposite side of the incident rays.

  • Above the principal axis, the height is considered positive, while below the principal axis, the height is considered negative.

  • Objective distance is considered positive, the real image distance is considered positive, and virtual image distance is considered negative. 

  • Magnification of the real image is considered negative and that of the virtual image is considered positive.

FAQs (Frequently Asked Questions)

Question 1: Can a Convex Lens Form an Image the Same Size as that of the Object?

Answer: Yes!

When an object is placed at a distance u = 2f from the optical center of the lens, the image formed by the convex lens will be the same size as that of the object.

Below is the ray diagram for the same:

[Image will be Uploaded Soon]

Question 2: Write Two Points on the Concave Lens.

Answer: 

  • A convex lens is a converging lens, so after refraction, rays coming from the distant source meet at a specific point or appear to meet at that point.

  • The image formed by the convex lens can be real, virtual, enlarged, diminished based on the position of the object.

Question 3: Write Two Points on the Concave Lens.

Answer: 

  • A concave mirror is a diverging lens, so after refraction, the rays diverge at various points.

  • The nature of the image formed by a concave lens is virtual and diminished (negligible in its size).

Question 4: Write a Few Applications of a Mirror and a Lens.

Answer: The applications of a mirror and a lens lie hereunder:

Lens

We can find lenses in microscopes, our wearing glasses, telescopes, magnifying glasses, etc.


Mirrors

We can see mirrors in automobile headlights, solar appliances, houses, etc. 

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