Plane Mirrors - Definition, Image Formation, Applications, Uses, FAQs

Edited By Vishal kumar | Updated on Jul 02, 2025 05:08 PM IST

Plane mirrors are fairly common in our daily lives. Even if the typical person is unfamiliar with this scientific phrase, they may easily compare it to ordinary mirrors that are polished on one side with mercury so that light falling on them can be reflected. In this article, we will discuss what is plane mirrors, the characteristics of plane mirrors, image formation by plane mirrors, laws of reflection, plane mirror ray diagram, characteristics of image formed by plane mirrors, and plane mirror examples and uses.

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What is Plane Mirror?
Characteristics of Plane Mirror
Image Formation by Plane Mirror
Virtual Image Of Plane Mirrors
Laws of Reflection
Characteristics of Image Formed by Plane Mirrors
Plane Mirror Examples And Uses

Plane Mirrors - Definition, Image Formation, Applications, Uses, FAQs

What is Plane Mirror?

Plane mirror definition: A plane mirror is described as a mirror having a flat surface and no inward or outward curve. They may easily reflect light in a variety of directions, resulting in refraction, absorption, or reflection on a plane mirror. In plane mirrors, at least two rays are required to build a picture of the object by examining the endpoints of the two light rays taken. The plane mirror can be polished with a variety of materials and used for a variety of purposes, but regardless of the material used in its construction, all mirrors work the same way.

Regardless of whether the image is real or virtual, the angle at which the ray is reflected by a plane mirror is equal to the angle at which the ray of light is incident, where the angle of incidence is the angle image formed by a plane mirror at an imaginary surface normal to the mirror (which is perpendicular to the surface) at the point of incidence. The angle created at the point between the contact of the reflected ray and the surface normal to the plane mirror is known as the angle of reflection.

Characteristics of Plane Mirror

The image formed by a plane mirror appears behind the screen hence it cannot be projected.
The image is upright and oriented the same way as the object and both sides are reversed.
The size of the image is the same as the object, unlike a convex mirror.
The distance from the mirror to both the image and the object is equal.

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$d_{image} = d_{object}$

Laws of reflection are obeyed.
A plane mirror provides a limited field of view

Image Formation by Plane Mirror

A person must be in the line of sight of the mirror to see any image in the mirror. When a person is in the line of sight of the mirror, the reflected ray reaches that person's eye, through which anyone can see the image of the object if they are in the line of sight of the mirror because light moves in a straight line. The fundamental properties of a plane mirror are that the objects' reflections produce a virtual image with the same magnification, size, and distance as the object itself.

Image formation by plane mirror

The picture of the object is determined by the geometrical line that a person sees in the mirror, yet the image of the object can be seen from any line of sight as long as the person's eye is in line with the mirror. The picture created is on the opposite side of the mirror, with the image's distance from the surface equal to the object's distance from the surface, which explains why a person can see exactly what is behind him.

Virtual Image Of Plane Mirrors

Plane mirrors are used to create virtual images of items because they are polished on one side, allowing the reflection of the object to strike the mirror and be mirrored in the direction of the observer's eye. As a result, the observer sees the image at the same distance from the mirror as the object. The magnification, size, and distance of the item are all the same in the picture generated by the flat mirror. These virtual plane mirror pictures are not produced on the screen in the same way that a genuine image is.

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Laws of Reflection

Two general reflection laws can be stated as follows:

The incidence angle (i) is always equal to the reflection angle (r).

$θ_{i} = θ_{r}$

The incident ray, the reflected ray, and the normal at the point of incidence are all in the same plane.

A plane mirror ray diagram: For the spectator, the incident light rays from the item produce an apparent mirror image.

ray diagram of plane mirror

Characteristics of Image Formed by Plane Mirrors

Characteristics of the plane mirror:

1. The plane images created by plane mirrors are always virtual.

2. The plane images created by flat mirrors are erect/ upright and of equal size to the item.

3. The plane mirror image creates an image that is the same size as the thing.

4. The plan mirror creates an image with the same magnification as the object.

5. One of the plane mirror's most distinguishing features is that the image it produces is inverted; for plane mirror examples, if you lift your left hand, the plane mirror's image will show your right hand moving upwards.

Plane Mirror Examples And Uses

Without a doubt, the invention of mirrors is the most significant contribution to physics. For several reasons, almost everyone else uses mirrors in their daily lives. We also know that plane mirrors are primarily utilized to see an object's reflection. Plane mirrors can be found in periscopes and kaleidoscopes, cars, shaving mirrors, dentists' mirrors, torch lights, solar cookers, and security-related applications.

Periscopes and Kaleidoscopes use plane mirrors:

Plane mirrors are commonly employed in the manufacture of kaleidoscopes, which are popular among youngsters, and periscopes, which are used solely in submarines. The plane mirror used in submarine periscopes reflects the plain images of all the ships present on the water's surface. Kaleidoscopes employ plane mirrors colored red glass to reflect a variety of colorful patterns.

Torch lights use plane mirrors:

Plane mirrors are commonly used in flashlights and torch lights to reflect light beams, and they are also employed in overhead projectors for the same purpose. Plane mirrors in torchlight can be utilized for finding or looking for things at night and in dark regions with such purposes and applications.

Plane mirrors are used for security and safety:

Plane mirrors are commonly used to locate bombs beneath vehicles. They're also used at shops and stores to keep an eye on consumers and avoid robberies. Mirrors are utilized even on blind corners on busy roads to view vehicles approaching from the opposite direction.

Other examples are:

Terrestrial telescope
Decorative mirrors
Laser reflectors

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Frequently Asked Questions (FAQs)

1. What is the purpose of a plane mirror?

Plane mirrors are commonly used to locate bombs beneath vehicles. They're also used at shops and stores to keep an eye on consumers and avoid robberies. Mirrors are utilised even on blind corners on busy roads to view vehicles approaching from the opposite direction.

2. Is the plane mirror image virtual and erect?

Plane mirrors are the only type of mirror that always produces a virtual, erect, and similarly sized picture from a real thing. Virtual objects, on the other hand, produce genuine visuals. A plane mirror's focal length is infinity, and its optical power is 0.

3. What are the three applications for plane mirrors?

Solar cookers make use of them.

They're also utilized to make periscopes, which are employed on submarines.
They're also used to build kaleidoscopes, which are toys that create lovely patterns.
They're also found in a wide range of scientific devices.

4. What is the best way to determine if an image is inverted?

The image is considered to be real and inverted when it is on the same side of the mirror as the item and the image distance is positive. The image of the object is considered to be virtual and upright when it is behind the mirror and the image distance is negative.

5. Is the size of your photograph the same as yours?

If you're looking for an image created by a flat mirror, your picture will be the same size as you are. The angle at which light rays strike a planar mirror is equal to the angle at which they are reflected.

6. How does a plane mirror affect the orientation of an image?

A plane mirror preserves the vertical orientation of an object but reverses its horizontal orientation. This means the image appears upright (not inverted top-to-bottom) but laterally inverted (reversed left-to-right).

7. Can a plane mirror produce a real image?

No, a plane mirror cannot produce a real image. It only forms virtual images because the reflected light rays do not actually converge at the image point. Real images, which can be projected onto a screen, are only formed by curved mirrors or lenses.

8. What is meant by lateral inversion in plane mirrors?

Lateral inversion refers to the left-right reversal of an image in a plane mirror. For example, if you raise your right hand, your image in the mirror appears to raise its left hand. This occurs because the mirror swaps the left and right sides of the object relative to the observer.

9. What is the field of view of a plane mirror?

The field of view of a plane mirror is the area that can be seen in the mirror from a given position. It depends on the size of the mirror and the observer's distance from it. A larger mirror or a closer viewing position increases the field of view.

10. Why do objects in a plane mirror appear to be reversed left to right but not top to bottom?

Objects in a plane mirror appear reversed left to right due to the way our brains interpret the reflected image. The mirror doesn't actually flip the image; instead, it swaps the left and right sides relative to the observer's perspective. The top-bottom orientation remains unchanged because the mirror is typically vertical, preserving the up-down relationship.

11. What is a plane mirror?

A plane mirror is a flat, smooth reflecting surface that produces virtual images of objects placed in front of it. It reflects light rays according to the law of reflection, where the angle of incidence equals the angle of reflection.

12. What is the relationship between object distance and image distance in a plane mirror?

In a plane mirror, the object distance (the distance from the object to the mirror) is always equal to the image distance (the apparent distance from the image to the mirror). This creates the illusion that the image is as far behind the mirror as the object is in front of it.

13. How does image formation occur in a plane mirror?

Image formation in a plane mirror occurs when light rays from an object reflect off the mirror's surface. The reflected rays appear to come from behind the mirror, creating a virtual image that is the same size as the object, upright, and laterally inverted.

14. Why is the image in a plane mirror called virtual?

The image in a plane mirror is called virtual because the light rays do not actually pass through the image point. Instead, they only appear to originate from that point behind the mirror. Virtual images cannot be projected onto a screen.

15. How does the size of the image compare to the size of the object in a plane mirror?

In a plane mirror, the size of the image is always equal to the size of the object, regardless of the object's distance from the mirror. This is because the light rays maintain their relative angles after reflection, preserving the object's proportions.

16. What is the principle behind an infinity mirror?

An infinity mirror creates the illusion of a never-ending tunnel of light using two parallel plane mirrors facing each other. One mirror is partially transparent, allowing some light to pass through. When a light source is placed between the mirrors, it creates a series of reflections that appear to recede infinitely.

17. What is the principle behind a retroreflector, and how does it differ from a plane mirror?

A retroreflector, unlike a single plane mirror, reflects light back to its source regardless of the angle of incidence. It often consists of three mutually perpendicular plane mirrors forming a corner cube. This arrangement ensures that incoming light undergoes three reflections, reversing its direction. Retroreflectors are used in road signs and safety equipment.

18. How do plane mirrors relate to the concept of parity in physics?

Plane mirrors illustrate the concept of parity transformation in physics. A parity transformation is equivalent to a reflection in a mirror, reversing all spatial coordinates. The behavior of most physical phenomena remains unchanged under parity transformation, just as the laws of physics appear the same in a mirror world.

19. How do plane mirrors relate to the concept of phase conjugation in optics?

While plane mirrors themselves don't perform phase conjugation, they help illustrate the concept. Phase conjugation is like "time-reversal" of a wave, similar to how a plane mirror reverses the direction of a light ray. Advanced phase conjugate mirrors can undo distortions in a wavefront, a property not possible with simple plane mirrors.

20. How does the angle of incidence affect reflection in a plane mirror?

In a plane mirror, the angle of incidence (the angle between the incoming light ray and the normal to the mirror surface) is always equal to the angle of reflection (the angle between the reflected ray and the normal). This relationship is known as the law of reflection.

21. What happens to parallel light rays when they reflect off a plane mirror?

When parallel light rays reflect off a plane mirror, they remain parallel after reflection. The mirror preserves the angle between the rays, maintaining their parallel relationship. This property is why plane mirrors do not focus or disperse light like curved mirrors do.

22. How does the material of a plane mirror affect its reflective properties?

The material of a plane mirror significantly affects its reflective properties. Most high-quality mirrors use a thin layer of silver or aluminum deposited on glass. The smoothness and purity of this metallic layer determine the mirror's reflectivity. Impurities or roughness in the surface can reduce the quality of reflection.

23. What is the difference between specular and diffuse reflection in relation to plane mirrors?

Specular reflection occurs on smooth surfaces like plane mirrors, where incoming light rays are reflected at the same angle as they arrive, creating a clear image. Diffuse reflection happens on rough surfaces, where light is scattered in many directions, not producing a clear image. Plane mirrors exhibit specular reflection.

24. How does the wavelength of light affect its reflection in a plane mirror?

In an ideal plane mirror, the wavelength of light does not affect its reflection. All visible wavelengths are reflected equally, preserving the color of the original object. However, in real mirrors, there might be slight variations in reflectivity for different wavelengths due to the properties of the reflective coating.

25. What is the role of the glass in a typical plane mirror?

In a typical plane mirror, the glass serves as a substrate for the reflective coating and protects it from damage. The glass itself is not the primary reflective surface. Instead, a thin metallic layer (usually silver or aluminum) applied to the back of the glass provides the reflective properties.

26. How does the thickness of a plane mirror affect the image?

The thickness of a plane mirror doesn't directly affect the primary image formation. However, it can create secondary reflections or ghost images. These occur when light reflects off both the front surface of the glass and the metallic backing, creating a faint double image, especially noticeable with bright objects against dark backgrounds.

27. Can a plane mirror magnify an image?

No, a plane mirror cannot magnify an image. It always produces an image that is the same size as the object. Magnification occurs in curved mirrors (like concave mirrors) or lenses, but not in flat plane mirrors.

28. How do plane mirrors contribute to the periscope principle?

Plane mirrors are essential in periscopes, which allow viewing objects from a concealed position. In a basic periscope, two plane mirrors are placed at 45-degree angles to the viewing direction, offset by 90 degrees from each other. This arrangement reflects light to change its path by 90 degrees twice, enabling the viewer to see around obstacles.

29. How do plane mirrors contribute to solar energy applications?

In solar energy applications, arrays of plane mirrors, known as heliostats, are used to reflect and concentrate sunlight onto a central receiver in solar power towers. These mirrors track the sun's movement to maximize energy collection throughout the day, demonstrating a practical application of the law of reflection.

30. What is the principle behind a kaleidoscope, and how do plane mirrors play a role?

A kaleidoscope uses multiple plane mirrors arranged in a tube, typically forming a triangle or other polygon when viewed end-on. Small, colorful objects are placed at one end. As light reflects off these objects and bounces between the mirrors, it creates symmetrical patterns due to multiple reflections, resulting in beautiful, ever-changing images.

31. How do plane mirrors affect the perception of space in interior design?

In interior design, plane mirrors are used to create the illusion of more space. When placed strategically, they reflect light and the surrounding area, making rooms appear larger and brighter. This effect is based on the virtual image property of plane mirrors, where the reflected space seems to extend beyond the mirror's surface.

32. What is the working principle of a corner reflector, and how does it relate to plane mirrors?

A corner reflector consists of three mutually perpendicular plane mirrors forming a corner. This arrangement reflects light back in the direction it came from, regardless of the angle of incidence. This principle is used in road signs and bicycle reflectors. It works because the light undergoes three reflections, each reversing one coordinate, ultimately sending the light back to its source.

33. How do plane mirrors contribute to the functioning of a sextant?

A sextant, used for celestial navigation, employs two plane mirrors. One is half-silvered, allowing partial transmission and reflection. The other is fully reflective and movable. By adjusting the angle of the movable mirror, navigators can superimpose the image of a celestial body on the horizon, allowing precise measurement of its angular height for determining position.

34. What is the relationship between plane mirrors and the law of conservation of energy?

Plane mirrors demonstrate the law of conservation of energy in optics. When light reflects off a perfect plane mirror, all the incident light energy is reflected without loss. In reality, a small amount of energy is absorbed by the mirror, slightly warming it, but the vast majority is reflected, preserving the energy of the light waves.

35. How do plane mirrors relate to the concept of time reversal symmetry in physics?

Plane mirrors illustrate time reversal symmetry in physics. If you were to film an object approaching a mirror and then moving away after reflection, playing the film backward would look physically identical to the forward version. This symmetry arises because the laws of reflection are the same whether time moves forward or backward.

36. What is the significance of plane mirrors in laser cavities?

In laser cavities, plane mirrors are crucial components. They form the ends of the optical resonator, reflecting light back and forth through the gain medium. One mirror is typically fully reflective, while the other is partially transmissive, allowing the laser beam to exit. The precise alignment of these mirrors is critical for laser operation.

37. How do plane mirrors contribute to the creation of holograms?

While plane mirrors themselves don't create holograms, they play a role in holography setups. Mirrors are used to direct and split laser beams, creating reference and object beams necessary for hologram recording. The precise control of light paths enabled by plane mirrors is essential for the interference patterns that form holograms.

38. What is the concept of mirror symmetry, and how does it relate to plane mirrors?

Mirror symmetry, or reflection symmetry, is when one half of an object is the mirror image of the other half. Plane mirrors physically demonstrate this concept. An object and its reflection in a plane mirror exhibit perfect mirror symmetry, with the mirror plane acting as the line or plane of symmetry.

39. How do plane mirrors affect polarized light?

Plane mirrors generally do not affect the polarization state of light upon reflection. However, when light reflects off a plane mirror at non-normal incidence (not perpendicular to the surface), it can induce a phase shift between the s and p polarization components, slightly altering the polarization state. This effect is more pronounced at larger angles of incidence.

40. How do plane mirrors contribute to the functioning of optical interferometers?

In optical interferometers, such as the Michelson interferometer, plane mirrors are essential components. They reflect light beams to create path differences, allowing for precise measurements of wavelength or distance. The high precision and predictability of reflection from plane mirrors make them ideal for creating controlled interference patterns.

41. What is the relationship between plane mirrors and the principle of least time (Fermat's principle)?

Plane mirrors demonstrate Fermat's principle, which states that light takes the path that requires the least time. In a plane mirror, the path of light from source to mirror to observer is always the shortest possible path, consistent with the law of reflection. This principle explains why the angle of incidence equals the angle of reflection.

42. What is the significance of plane mirrors in optical cloaking devices?

While plane mirrors themselves are not optical cloaks, they inspire some cloaking designs. Advanced cloaking devices often use principles of reflection and redirection of light, similar to how plane mirrors reflect light. Some cloaking concepts involve arranging reflective surfaces to guide light around an object, making it appear invisible.

43. How do plane mirrors contribute to the study of quantum optics?

In quantum optics, plane mirrors are used in various experimental setups. They help create optical cavities for studying light-matter interactions at the quantum level. The predictable behavior of light reflection from plane mirrors is crucial for designing experiments that probe fundamental quantum properties of light.

44. What is the relationship between plane mirrors and the principle of reversibility in optics?

Plane mirrors exemplify the principle of reversibility in optics, which states that light can follow the same path in reverse. If a light ray travels from point A to point B via reflection off a plane mirror, it can also travel from B to A along the exact same path. This principle is fundamental to many optical systems and calculations.

45. How do plane mirrors relate to the concept of optical path length?

Plane mirrors preserve optical path length in reflections. The total path length of a light ray from source to mirror to observer is the same as if the light traveled directly from the source to the virtual image behind the mirror. This property is crucial in understanding interference effects and in designing optical systems.

46. What is the role of plane mirrors in creating optical illusions?

Plane mirrors are fundamental to many optical illusions. They can create virtual images that appear to be in impossible locations, make objects seem to float, or create infinite reflections. Illusions like the Pepper's Ghost effect use partially reflective plane mirrors to superimpose virtual images onto real scenes, creating ghostly apparitions.

47. How do plane mirrors contribute to the study of light polarization?

While plane mirrors generally don't alter light polarization at normal incidence, they can be used in setups to study polarization effects. For instance, in ellipsometry, plane mirrors are part of systems that measure changes in polarization upon reflection from surfaces, providing information about material properties.

48. What is the significance of plane mirrors in laser rangefinding technology?

In laser rangefinders, plane mirrors are often used to direct laser beams precisely. The known properties of reflection from plane mirrors allow for accurate calculation of distances based on the time it takes for a laser pulse to travel to a target and back. This principle is used in surveying, autonomous vehicles, and military applications.

49. What is the role of plane mirrors in creating optical resonators?

Plane mirrors are crucial in creating optical resonators, which are fundamental to laser operation. Two parallel plane mirrors can form a Fabry-Pérot cavity, trapping light between them. The precise alignment and reflectivity of these mirrors determine the resonator's properties, affecting laser output characteristics.

50. How do plane mirrors contribute to the study of light coherence?

Plane mirrors are used in experiments studying light coherence, such as in interferometers. By reflecting and recombining light beams, they allow for the observation of interference patterns. The quality and flatness of plane mirrors are crucial in maintaining the coherence of light in these experiments.

51. What is the significance of plane mirrors in optical computing concepts?

In optical computing concepts, plane mirrors play a role in directing and manipulating light signals. They can be used to create optical logic gates or to route optical signals in proposed photonic circuits. The predictable behavior of light reflection from plane mirrors is valuable in designing such systems.

52. How do plane mirrors relate to the concept of wavefront reconstruction in holography?

While plane mirrors don't directly reconstruct wavefronts, they are used in holographic setups. Mirrors help direct reference and object beams in hologram recording. In playback, the precise reflection properties of plane mirrors can be crucial in reconstructing the original wavefront from the hologram.

53. What is the role of plane mirrors in creating optical delay lines?

Plane mirrors are essential in optical delay lines, which are used to introduce controlled time delays in optical signals. By reflecting light back and forth between multiple mirrors, the path length can be increased, creating a time delay. This is useful in various applications, including optical signal processing and interferometry.

54. How do plane mirrors contribute to the study of nonlinear optics?

In nonlinear optics experiments, plane mirrors are often used to direct high-intensity laser beams precisely. While the mirrors themselves don't exhibit nonlinear effects, their ability