Difference Between Mirror and Lens

The use of a mirror can be traced back to 4000 BC, when water was put in a dark bowl or container. The first use of the lens can be traced back to 1888 and was used for correcting vision. Even today, mirrors and lenses find use in many areas.

They are made in different shapes and sizes depending upon their needs and wants.

We use a mirror every day to look at ourselves. A lens is used in telescopes. It helps us to understand space and the universe. With the help of these, we have been able to uncover many secrets of the universe.

Mirror vs Lens

The main difference between a mirror and a lens is that the mirror works on the principle of reflection while a lens operates on the principle of refraction. The majority of mirrors are opaque for better reflection, whereas a lot of lenses made are transparent of the formation of images.

Mirror vs Lens

The law of reflection describes how a mirror creates an image. It claims that when light strikes an opaque material and is bounced, the angle of reflection is equal to the incident ray, and in the centre of these degrees is a perpendicular standard.

Everybody uses a lens in some form or another every day. They can be used to read small letters in a book with a magnifying glass, magnify or minimize images and bring blurry images into focus.

A lens is a transparent medium that comes in different shapes and is used to bend light in a specific way. This can mean that the rays either diverge or converge from a specific point.

Comparison Table Between Mirror and Lens

Parameters of ComparisonMirrorLens
PrincipleWorks on the principle of reflectionWorks on the principle of refraction
Image formation formula1/v+1/u=1/f   1/v-1/u=1/f  
ConstructionMostly opaque for light reflectionMostly transparent for image formation
Focal pointsA plane mirror has no focal pointHas to focal points, F and 2F
Distance of the objectMeasured from the pole(P)Measured from the optical centre
ShapeA mirror can be both curved and plane depending upon the useThe lens is of the ellipsoid, biconvex shape. An ellipsoid is similar to a sphere but stretched out, like an olive, and biconvex means it’s rounded outward on both sides.

What is Mirror?

Image formation by a mirror can be understood by the law of reflection. It states that when light hits an opaque surface and is reflected, the angle of reflection is equal to the incident ray, and there is a perpendicular normal in the middle of these angles.

Incident Ray- It is the ray of light that travels towards the opaque surface of the mirror and falls on it.

Reflected ray – It is the ray of light that is reflected back after hitting the opaque surface of the mirror. The incident ray and the reflected ray construct equal angles from the normal on either side of the normal.

Three main types of mirrors are:

  1. Plane mirror-This is the most commonly used mirror. The light ray which hits them is reflected back at an angle of 90°. The image that you see in the mirror is reversed. This means that the right side appears to be the left side, and the left appears to the right. This is called a mirror image.
  2. The convex mirror-This mirror forms a virtual image and is called in the outward direction.
  3. Concave mirror-Both real and virtual images can be formed. It bends outwards. If the image is placed at infinity, a highly diminished but real image is formed. If the object is placed between the focus and the pole, the image formed is highly magnified and virtual. This finds application in shaving mirrors.

Some other mirrors that are used in physics are:

  1. Rotating mirrors
  2. Inclined mirrors
  3. Spherical mirrors

Ray diagrams can also be built on paper to predict the position of the image formed by a mirror. The diagrams can also be used to predict the shape, size, and distance of the image and also whether it will be real or virtual.

What is Lens?

The lens is used in many ways every day. Some examples are camera lenses, prime lenses, telephoto lenses, eyeglass lenses, and contact lenses.

Lenses are made from plastic or glass, and the shape in which they are constructed decides whether the light passing through it will diverge or converge.

The law says that moving from a lower refractive index to a larger refractive index, for example, from air to water, the ray of light will be reflected in the direction of the normal of the surface vice versa is also true.

In real life, it can be difficult to understand the direction in which the ray of light is moving through the lens.

Ray diagrams become extremely useful in these cases as they can be used to determine the direction of movement of the light and also the place where the image will be formed based on the location of the lens and object.

This is done by using Snell’s law of refraction. Images formed by a lens can be of two types, a real image and a virtual image.

A real image is formed when the rays of light from the lens actually converge at a point and are visible to the naked eye. This means that the image is formed on the receptors of the human eye, and the photo-sensitive cells actually pick it up.

A virtual image is formed when the rays of light through the lens make it look like they are coming from the virtual image. This means that if you follow the race of light backwards, you will reach the point where they all converge.

In truth, these rays don’t actually converge at this location, and if a screen is placed at this point, an image will not be visible.

Main Differences Between Mirror and Lens

  1. Lens operates on the principle of refraction, while mirrors operate on the laws of reflection.
  2. 100% of the light is reflected and refracted in the case of an ideal mirror and lens, respectively.
  3. There are mainly 6 different types of the lens, while the mirror exists only in broadly concave and convex mirrors.
  4. The lens has 2 focal points, while a plane mirror has 0 focal points.
  5. 1/v-1/u=1/f is the formula for image formation by a lens. On the other hand, 1/v+1/u=1/f is the formula for image formation by a mirror.
Difference Between Mirror and Lens

Conclusion

A lens is a transparent medium that comes in different shapes and is used to bend light in a specific way. This can mean that the rays either diverge or converge from a specific point. Lenses are made from plastic or glass.

The shape in which they are constructed decides whether the light passing through it will diverge or converge. Ray diagrams are used to trace the movement and direction of the rays of light.

These give us an understanding of the place where the image is formed and the place where light rays converge.

Have you ever wondered why images are visible in a mirror and not on the wall all the both of them are plain? This is because the surface of the microscopic level is very smooth.

The surface of the wall is rough, and the light is reflected in every direction causing a diffused reflection. The reflection occurring from the mirror is known as specular reflection.

References

  1. https://bjo.bmj.com/content/78/10/775.short
  2. https://aapt.scitation.org/doi/abs/10.1119/1.15254
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