Difference Between Convex and Concave Mirror

Edited by Diffzy | Updated on: July 03, 2023

       

Difference Between Convex and Concave Mirror

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Introduction

Mirrors are a part of our daily life. We use these mirrors without knowing the types of mirrors, the principle behind them, and how these were modified. A mirror is a reflecting surface. Mirrors obey the law of reflection states that the incident light ray, the reflecting ray, and the Normal lie on the same plane, and the angle of incidence is the same as the angle of reflection. We have plane mirrors, concave mirrors, and convex mirrors. A plane mirror is for daily use, and the other two are used based on purpose. Before we go deep into what concave and convex mirrors are, let us understand some of the basic terms.

Incident Ray

It hits the mirror from an external source.

Reflected Ray

It comes out of the mirror after hitting.

Normal Ray

It is perpendicular to the mirror surface.

The Angle Of Incidence

It is between the incident ray and the Normal ray.

The Angle Of Reflection

It is between the reflected ray and the Normal ray.

Concave Mirror vs Convex Mirror

Concave and convex mirrors are types of spherical mirrors. These form a part of a whole sphere. A concave mirror forms if you paint the outer surface of a sphere. A convex mirror forms if you paint the inner surface of a sphere. A concave mirror is curved inwards, and a convex mirror is curved outwards.

Terms used in the context of concave and convex mirrors:

  • Pole(p): the centre point of the mirror.
  • Centre of curvature(c): the midpoint of the sphere from which the mirror forms.
  • The radius of curvature(r): the distance between the pole and the centre of curvature.
  • Principal of axis: the imaginary line passing through the Pole and centre of curvature.
  • Focus(f): a point on the principle of the axis.

Difference Between Concave And Convex Mirror In Tabular Form

Basis of ComparisonConcave MirrorConvex Mirror
Reflecting SurfaceThe reflecting surface is inwards.The reflecting surface is outwards.
Focal PointFocal point is in front of the mirror.It is behind the mirror.
TypeIt is a converging mirror.It is a diverging mirror.
The image formedIt forms different types of images.It forms only virtual, diminished, and erect images.
Type of ImageIt forms Real or virtual, inverted erect images.It forms virtual and erect images.
Magnification Of imageIt produces magnified or diminished image.It produces diminished image.
ApplicationsUsed in telescope,  torch, and headlights.Used in the rearview mirror, and fisheye mirrors.
Projected on screen.The image can be projected on the screen.The image cannot be projected on a screen.

What Is A Concave Mirror?

A concave mirror is polished inside and painted outside. It is hollow and curved inwards.

Features Of A Concave Mirror

  1. These are converging mirrors.
  2. A magnified and virtual image forms if the object is close to the mirror.
  3. As the object moves far from the mirror, the image size reduces and becomes a Real image.
  4. The focal point and centre of the curvature lie ahead of the mirror.

Images Formed By Concave Mirror

  • If the object is at infinity, the image forms at the Focus. The parallel rays come from infinity, incident on the mirror, and the rays converge at the Focus to form a Real, inverted, and point size image.
  • If the object is beyond the centre of curvature, the image forms between F and C. One parallel ray and another moving towards C after reflection forms a Real, diminished, and inverted image.
  • The image is formed at C if the object is at C. Two parallel rays, after reflection, pass through the focus and form a Real, inverted image the same size as the object.

The image is formed at ♾️ if the object is at F. One parallel ray and another ray pass through C, and after reflection, the image formed is Real,

  • Inverted and highly enlarged.
  • If the object is between F and P, the image forms behind the mirror as virtual, erect, and enlarged.
Position of the objectPosition of the imageNature of the imageSize of the image
InfinityFReal, invertedPoint sized
Beyond CBetween F and CReal invertedDiminished
At CAt CReal, invertedSame size
At FInfinityReal,  invertedHighly enlarged
Between F and PBeyond the mirrorVirtual, erectEnlarged

Applications Of The Concave Mirror

  • Shaving mirrors: concave mirrors produce an Erect and enlarged image required for shaving.
  • Optical instruments: concave mirrors are used in optical cavities for lasers and other optical instruments.
  • They're used as makeup mirrors, often with a magnification effect, so that people can see a detailed and enlarged view of their face so that they can apply it precisely. In dental practice, cave mirrors provide a clearer view of the teeth and mouth during oral examinations.
  • Astronomical telescope: a converging mirror of a diameter of more than 5 m used as an object.
  • Headlights of automobiles: the point light is kept at the Focus so the reflected rays cover long distances.
  • Solar furnaces: large converging mirrors focus the light at the centre of the furnace to produce heat. These are used for cooking, heating, and melting metals.
  • Concave mirrors in solar power systems act as reflective concentrators. The mirrors concentrate the sunlight on a smaller area, such as solar panels or receivers, to increase its intensity and energy conversion.
  • These are used in modern air crafts for landing.
  • The base of the microscope's condenser serves as a concave mirror. This enables the mirror to focus the light that passes through it and ensure that the area around the object is black. This technique allows us to see the object or specimen.

What is a Convex Mirror?

A convex mirror is bulged outwards. The outer surface is polished, and the inner surface is painted. The bulged surface acts as a reflecting surface. Fish eye mirrors are another name because they are diverging mirrors. When the light rays focus on the mirror, upon reflection, these rays scatter away from the mirror.

The Convex mirrors are designed to deal with outdoor conditions. These are usually manufactured with materials that can withstand weather conditions such as rain, snow and UV radiation. This durability makes them suitable for outdoor applications where visibility is crucial, even in challenging weather conditions.

Due to the shape, Convex mirrors produce an uneven reflection. Objects in the convex mirror seem smaller and more distant than they are. As objects come closer to the mirror surface, this distortion increases.

A plane mirror produces an image the same size as the object whereas the concave lens produces an enlarged image if the object is near the mirror. What images do convex mirrors produce? When you look at the mirrors near the entrance gates, you find yourself very tiny. So convex mirrors produce small-sized images compared to the object.

Features Of The Convex Mirror

  • These mirrors deviate the light rays away from the reflecting surface.
  • The images formed are always virtual, diminished and erect images.
  • The screen cannot project the images as they are virtual.
  • The images are not Real because the centre of curvature and the F is behind the mirror and the image forms behind the mirror.

Types Of Images Formed

As we already know, convex mirrors always produce virtual and erect images.

When the object is at infinity, the image forms behind the mirror at the F. Unlike in the concave mirrors, the resulting image is virtual, erect and highly diminished.

A diminished, virtual and erect image is produced between pole and F of the mirror if the object is placed between the infinity and pole.

Position of the objectPosition of the imageSizeNature
At infinityFocusHighly diminished             Virtual and erect
Between pole and infinity Between pole and focusdiminishedVirtual and erect

Applications of Convex Mirrors

  • The common type of convex mirror we see daily is the fish eye mirror. It is used at the entrance gates so the vehicles do not bump into each other.
  • 'Objects are smaller than they appear'- we read this line daily in the rearview mirrors of automobiles. The objects appear smaller because of the convex mirror used. These will let the drivers have a clear and wide view of the vehicles and surroundings behind them. These mirrors ensure the safety of the vehicles.
  • Two convex mirrors make magnifying glasses.
  • These are used in street lights as they can scatter the light to larger areas.
  • Convex mirrors are used in ATMs to let people know if someone is standing behind them. It is used for security purposes and prevents theft.
  • Some mobile cameras use convex mirrors in their lens too.
  • Sunglasses reflect the sunrays and protect our eyes from the harsh UV rays, so even sunglasses are made of convex mirrors.
  • These are used in homes as they bring an illusion of more space to the home.
  • These are used in industries and warehouses to improve safety.

Sign Convention

The universally used sign convention is the Cartesian sign convention. Appropriate signs must be used to calculate the distances and derive formulae for spherical mirrors. All the distances are measured from the pole of the mirror i.e. the pole is the starting point. The distances are measured along the principal axis.

  • The object is placed to the left of the mirror. So, the light rays fall on the mirror from the left-hand side.
  • All the distances are marked out from the pole of the mirror.
  • All the distances measured along the x-axis towards the right side are taken as positive, and all those towards the left side are taken as negative.
  • All the distances taken in the direction of incident lights are considered positive, whereas the opposite of the incident light is considered negative.
  • Distances estimated above the principal axis are positive.
  • Distances estimated below the principal axis are negative.

Mirror Formula And Linear Magnification

The mirror formula is used to solve the problems related to spherical mirrors. We can calculate the object distance, image distance, and the focal length. By using the above signs, we have just learned, we can obtain the results.

1/u +1/v = 1/f

Where, u = object distance

V= image distance

F= focal length

Now, how do we know if we got an enlarged image or a diminished image and their sizes? There is another formula called linear magnification to calculate the height of the object and the image.

M= h'/h= -v/u

If the M turned out to be positive, we get a real image and if it is negative, the image is virtual.

M = +ve ----à real image

M= -ve ---à virtual image

Main Differences Between Concave And Convex Mirrors in Points

  • Concave mirrors are curved inwards, and convex mirrors are curved outwards.
  • Images formed in a concave mirror are virtual or Real images, on the other hand, images formed in a convex mirror are virtual images.
  • The reflecting surface is towards the centre of the sphere in a concave mirror, whereas the reflecting surface is away from the centre of the sphere.
  • Concave mirror ----à converging mirror
  • Convex mirror ----à diverging mirror
  • Concave mirror: focus lies in front of the mirror.
  • Convex mirror: focus lies behind the mirror.
  • A concave mirror produces a magnified and diminished image, on the other hand, a convex mirror produces only a diminished image.
  • Images formed by a concave mirror and convex mirror can and cannot be projected on the screen respectively.

Conclusion

Concave and convex mirrors are a part of our daily life. Remembering their differences can be quite confusing, so here is a trick for you to master this concept. A cave's entrance is kind of curvy and opens inwards just like the concave mirror.

As the convex mirrors are diverging, the rays have to be extended back, so the image is formed behind the mirror. Real people (images) talk to people's faces, in front of them. The wide spectrum of applications of spherical mirrors makes our day easier.


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"Difference Between Convex and Concave Mirror." Diffzy.com, 2024. Mon. 20 May. 2024. <https://www.diffzy.com/article/difference-between-convex-and-concave-mirror>.



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