Plane Mirror

A plane mirror is a type of mirror that has a flat, reflective surface. It reflects light rays in a predictable manner. Plane mirror is generally used as dressing mirror. It forms a virtual and erect image. The size of the image is formed is same as that of object. In this article, we will learn in detail about the plane mirror, image formation by plane mirrors and its characteristics. We will also learn about the applications of plane mirror and compare it with spherical mirror, parabolic mirror and elliptical mirror.

What is Plane Mirror?

A plane mirror is a type of mirror that has a flat or plane reflecting surface. It reflects a replica of the object placed in front of it. It is polished at the back and reflects the surface from the front. It is commonly used in everyday life, such as in barbershops, cameras, microscopes or for decorative purposes. It comes in various shapes and sizes, such as circular and rectangular and is available in other designs.

Geometric Properties of Plane Mirrors

The properties of plane mirrors are mentioned below:

• Flat Surface: Plane mirrors have a flat and smooth reflective surface.
• Virtual Image Formation: Plane mirrors form virtual images. These images are upright, laterally inverted (left and right are reversed), and located behind the mirror at the same distance as the object in front of it.
• Size and Distance: The size and distance of the virtual image formed by a plane mirror are the same as that of the object.
• No Focal Point: Unlike concave mirrors, plane mirrors do not have a focal point. Light rays diverge after reflection, making them appear to come from behind the mirror.
• Field of View: The field of view of a plane mirror is limited by its size and the angle of incidence of light rays. It reflects the entire scene within its line of sight, without distortion.

Light Reflection in Plane Mirrors

When light rays get strokes over the flat mirror and get reflected. According to the laws of reflection, the angle of incidence is equal to the angle of reflection (∠ i =∠ r). Reflection of light is a process where a ray of light, emitted from a light source and incident upon a plane mirror, reflects into the same medium at the same angle is known as reflection of light. The image which is present in the mirror is obtained behind the plane. The image is virtual and erect, a reflection on a plane mirror.

There are two main Laws of Reflection:

• The angle of incidence (∠i) is equal to the angle of reflection(∠r). Mathematically, (∠i = ∠r).
• All three rays i.e. the incident ray reflected ray, and the normal at the point of incidence, all lie in the same plane.

Terms Related with the Reflection of Light

The terms associated with the process of reflection of light is discussed below:

• Incident Ray: The ray of light that falls on the reflecting surface from the object or a source is known as an incident ray.
• Reflected Ray: The ray of light that is supposed to be reflected after striking the reflecting surface is known as the reflected ray.
• Angle of Incidence: The angle that is formed between the incident ray and the normal at the point of incidence is known as the angle of incidence, generally represented by ∠i.
• Angle of Reflection: The angle formed between the reflected ray and the normal at the point of incidence is known as the angle of reflection, generally represented by ∠r.
• Normal: A straight line perpendicular to the reflecting surface that acts as a separation between the plane of incidence and the plane of reflection is known as the normal.

Images Formation by Plane Mirrors

Plane mirror reflects a replica of the object placed in front of them. When a light coming from an object falls on a plane mirror it bounce back or get reflected in the same medium at an angle equal to the angle of incidence. The reflected rays meet virtually or appears to meet behind the mirror forming an image of the object.

• The ray of light that falls on the reflecting surface from the object or a source is known as an incident ray.
• The ray of light that is supposed to be reflected after striking the reflecting surface is known as the reflected ray.

The characteristics of the image formed by plane mirror is discussed below:

Characteristics of Image Formed by Plane Mirror

The characteristics of the image formed by the plane mirror is mentioned below:

• The image formed through the plane mirror is always virtual (the image that cannot be obtained on-screen) and erect (Upright or straight).
• The size of the object and the size of the image are equal.
• The distance the object is placed is the same as the distance between the image obtained.
• Laterally inverted images, i.e., the object’s right side appears on the left side behind the mirror, are obtained.

Ray Diagram for Plane Mirror

A ray diagram is like a picture that shows how light moves when it hits a mirror. When we draw a ray diagram for a plane mirror, we’re drawing what happens when light shines on the mirror.

Parts of a Ray Diagram

• Mirror: Think of it as the surface of the mirror. We draw it as a straight line to show where the mirror is.
• Incoming Light Ray: This is the light coming from object, like the Sun or a lamp before it hits the mirror. We draw it as an arrow pointing towards the mirror.
• Reflected Light Ray: When the incoming light hits the mirror, it bounces back. We draw this bouncing light as an arrow pointing away from the mirror. It bounces back at the same angle it hit the mirror.
• Normal Line: This is like an imaginary line on the mirror at a right angle. We draw it as a dashed line.
• Image: The virtual copy formed by the plane mirror of the object that was created by the mirror which we can see with the naked eye.
• Object: Item that was placed in front of the mirror to create its virtual and lateral image by the plane mirror.

Mirror Equation for Plane Mirror

The mirror formula is given as

1/f = 1/v + 1/u

where,

• f is focal length which is half of radius of curvature in spherical mirrors
• v is image distance
• u is object distance

Now in case of plane mirror, radius of curvature is ∞

Then, focal length is R/2 = ∞/2 = ∞

Now putting the value of focal length in the mirror equation

⇒ 1/f = 1/v + 1/u

⇒ 1/∞ = 1/v + 1/u

⇒ 0 = 1/v + 1/u

⇒ -1/v = 1/u

⇒ u = -v

This shows that the distance of image is same as the distance of the object from the mirror. The negative sign indicates that the image is formed behind the mirror.

Magnification in Plane Mirror

In a plane mirror, the magnification is always 1. It means that the size of the image formed in the mirror is the same as the size of the object being reflected. When you stand in front of a plane mirror, you see your reflection at the same size as you are in reality. Magnification (m) is defined as the ratio of the size of the image (h_i) to the size of the object (h_o)

m = h_i / h_o

The magnification produced by the plane mirror is +1.

Proof:

Magnification Formula ⇒ m = h_i / h_o OR m = -v/u

Since, in plane mirror, we know that height of object is same as height of image

m = h_i/h_o

m = h_i/h_i = 1

Since, magnification is positive this shows image is virtual and erect

Examples of Plane Mirrors

Some of the examples of plane mirrors in everyday life is tabulated below:

Bathroom Mirror: The mirror you use to see yourself while brushing your teeth or grooming in the bathroom is typically a plane mirror. It reflects your image without distorting it.

Dressing Room Mirror: Mirrors in dressing rooms or clothing stores are often plane mirrors. They allow you to see how clothing fits on your body without any distortion.

Periscope: Periscopes, used in submarines and some military equipment, often contain plane mirrors. They reflect light to allow observers to see objects above the surface of the water while remaining submerged.

Teaching Mirrors: In educational settings, plane mirrors are often used to demonstrate principles of reflection and optics. They help students understand how light behaves when it interacts with surfaces.

Plane Mirror vs Spherical Mirror

A plane mirror is a flat mirror, meaning its surface is flat and reflects light without distorting the image. It reflects light according to the law of reflection, which states that the angle of incidence is equal to the angle of reflection.

Spherical mirror has a curved surface, either concave (curves inward) or convex (curves outward). Spherical mirrors are named as such because their reflecting surface forms a part of a sphere. The reflection of light from a spherical mirror follows more complex rules compared to a plane mirror, involving the focal point, focal length, and different image formations based on the position of the object.

Features	Plane Mirror	Spherical Mirror
Shape	Flat surface	Curved surface
Reflection	Reflects light rays in a predictable manner	Reflects light rays in a curved manner
Focal Point	Does not have a focal point	Has a focal point where parallel rays converge
Image Formation	Produces virtual, upright, and laterally inverted images	Produces both real and virtual images, depending on the object’s position in the mirror
Field of View	Reflects light from all directions uniformly	Reflects light from a specific region of space
Applications	Used in regular mirrors, periscopes, and rear-view mirrors	Used in telescopes, makeup mirrors, and reflectors
Image Quality	Reflections are undistorted and of uniform intensity	Reflections may suffer from spherical aberration and distortion near the edges

Plane, Parabolic and Elliptical Mirror

The comparison of plane mirror with parabolic and elliptical mirror is mentioned below:

Plane Mirror

• Plane mirror has a smooth and flat surface.
• It works on the law of reflection which states that the angle of incidence is equal to the angle of reflection.
• It create virtual images that are upright and also have a property named lateral inversion.
• They are commonly used in daily use such as mirrors on dressing tables, in saloons, kaleidoscopes.

Parabolic Mirror

• A parabolic mirror has a curved surface shaped like a parabola.
• It reflects light rays in a way that all incoming parallel rays converge at a single point called the focus (Focal length)
• Parabolic mirrors are used where focus or collect light at points such as reflecting telescopes, and solar concentrators.

Elliptical Mirror

• An Elliptical mirror has a curved shape like an ellipse.
• It has two focal points, with light rays directed towards one focal point reflecting towards the other focal point.
• Elliptical mirrors are used in optical devices such as headlamps in automobiles and some types of telescopes.

Uses of Plane Mirrors

Plane mirror are used for variety of applications. The detailed applications of plane mirrors are mentioned below:

Periscope: Submarines use periscopes to see objects on the water’s surface. It is impossible to bend light rays since they move in straight directions, although they can be reflected. The plane mirrors of a periscope adjust the direction of light rays so that the item can be seen by the submarine’s viewer.

Kaleidoscope: Because of the reflection, large flat mirrors can generate an optical illusion. To our eyes, the rooms appear to be larger. Inside a kaleidoscope, you get a similar view. Depending on the things present, the pattern can change. Small beads with basic patterns are usually found inside. A continuous pattern emerges from the reflections of the closely spaced flat mirrors.

Telescope: A telescope is used to observe distant objects in the solar system, such as planets. Telescopes are classified into two types. A set of lenses is used in a refracting telescope. Plane mirrors are used in conjunction with spherical mirrors in reflecting telescopes.

Saloon: We can create unlimited images by installing plan mirrors parallel to each other this trick allows the customer to view both the front and rear of a person.

SLR cameras: Single-lens reflex (SLR) cameras use plane mirrors.

Microscopes: Plane mirrors are used to reflect light onto the specimen to brighten it.

Surveillance Systems: Mirrors that are placed in a certain way can help people keep an eye on places that they cannot see directly. This can be useful in surveillance systems where people want to observe things without being noticed.

Education and Science: Plane mirrors are educational tools in science classrooms, to demonstrate the principles of optics and light reflection to students.

Navigation: In navigation tools such as sextants, plane mirrors aid in celestial navigation by reflecting light from celestial bodies, assisting sailors and navigators in determining their position relative to the horizon and celestial objects.

Decorative Purposes: Plane mirrors are used in interior design to create illusions of space by reflecting light and enhancing the appearance of rooms.

Conclusion

In conclusion, plane mirrors are a common type of mirror used in everyday life. They reflect a replica of the object placed in front of them, and the characteristics of the image formed by them are always virtual and erect. The laws of reflection determine the angle of incidence and angle of reflection when light rays strike the flat mirror and get reflected. The geometric properties of plane mirrors include a flat surface, virtual image formation, no focal point, and a limited field of view. They are commonly used in dressing tables, saloons, and periscopes. Parabolic and elliptical mirrors are other types of mirrors used in optical devices such as telescopes and headlights.

Frequently Asked Questions on Plane Mirror

Can a plane mirror magnify or reduce the size of an object?

No, a plane mirror does not magnify or reduce the size of an object. The size of the image formed by a plane mirror is the same as the size of the object.

What is a plane mirror and how does it differ from other types of mirrors?

A plane mirror is a flat, smooth mirror where the reflecting surface is a plane. It differs from other types of mirrors, such as concave and convex mirrors, in that it does not have any curvature.

What is the field of view of a plane mirror?

The field of view of a plane mirror is determined by its size and the angle of incidence of light rays. It reflects a wide field of view but is limited by the size of the mirror.

How does a plane mirror form an image?

A plane mirror forms an image by reflecting light rays from an object placed in front of it. The reflected rays create an apparent image behind the mirror.

Is plane mirror convex or concave?

No, plane mirror is neither convex nor concave

What type of image is formed by plane mirror?

Plane mirror form virtual, erect and image of same size as of the object

Do plane mirror form real and inverted images?

No, plane mirror doesn’t form real or inverted images