How Do Plane Mirrors Create Images?
Light is a form of energy that brings forth the sensation of sight in our eyes. The path of light is always a straight line, and this single beam of light is called a ray of light. The process of sending back the light waves after falling on the surface of an object is called a reflection of light. The reflection of an object over a plane mirror forms images at many different places.
Light has two important properties, viz: reflection, and refraction.
The process by which light waves falling on a surface is sent by the surface is called reflection.
The objects having smooth, shiny, or polished surfaces reflect more light as compared to objects having unpolished or rough surfaces.
The best reflector of light is silver. For this reason, a thin layer of silver metal is deposited on one side of the glass plate while making a plane mirror. This silver coating is protected by red paint.
Types of Reflection
There are basically two types of reflection:
Specular/Regular reflection
Diffused/Irregular reflection
a. Specular/Regular Reflection
It is the mirror-like reflection of light rays. In this case, the light rays are reflected from a smooth, shiny, or polished surface like that of a mirror, and are reflected by a definite angle. Here, the incident ray & reflected ray makes the same angle with the normal. The formation of an image is due to regular reflection.
b. Diffused/Irregular Reflection
Diffused/Irregular reflection is a non-mirror type of reflection of light. In this reflection, the rays of light hit an irregular object with a rough surface and are reflected back from the object and scattered in all directions.In this case, the incident ray and the reflected ray don't make the same angles with the normal. This is because the angle of incidence and the angle of reflection are different.
No image is formed by this type of reflection.
What are Laws of Reflection?
The laws of reflection of light can be applied both in the case of a plane mirror & the spherical mirror. Here, you can find detailed information regarding the images formed by the plane mirror.First law of reflection: It states that the incident ray, reflected ray, and the normal (perpendicular to the surface of the object) at the point of incidence, lie in the same plane.Second law of reflection: As per this law, the angle of reflection is always equal to the angle of incidence.
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Besides, one must bear in mind that when a ray of light normally falls (creating an angle of 90° with the surface) on the surface of a mirror, then both the angle of incidence and reflection will be zero. Moreover, this ray of light will be reflected back on the same path.
Plane Mirror Definition
A mirror with a flat or planar reflective surface is called a plane mirror. The reflected angle is always equal to the incident angle for all the light rays, which strike the plane mirror. The angle that occupies within the incident ray & the normal is called the angle of incidence. The normal is said to be an imaginary line that is perpendicular to the surface.
Reflection on a Plane Mirror
Here you will find a brief understanding of certain crucial terms, these are:
Incident Ray: The light ray that falls on the surface of a mirror is called the incident ray of light.
Point of Incidence: The incident ray that comes in touch with the surface of the mirror.
Ray: The light ray that is sent back by the mirror after striking the surface of the mirror is called the reflected ray.
Normal: It is an imaginary line perpendicular to the mirror's surface at the point of incidence.
Angle of Incidence: The angle made within the incident ray & the normal at the point of incidence is called the angle of incidence.
Angle of Reflection: The angle made within the reflected ray and the normal at the point of incidence is called the angle of reflection.
Images Formed by Plane Mirrors
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The nature of the image formed by a plane mirror is mentioned below:
The image is virtual and erect
The size of the object equals that of the size of the image.
An image is formed behind the mirror.
The distance between the image & the mirror is the same as the distance between the mirror and the object.
Image formed is laterally inverted.
The image is laterally inverted. This suggests, if you raise your left hand, it would appear that you have raised your right hand in the mirror.
Uses of Plane Mirror
Mirrors are used in the dressing table, bathrooms to see ourselves.They are usually placed in the inside walls of jewelry shops to make it look big.Mirrors are fitted at blind turns on the roads so that vehicles' drives can see vehicles coming from the other side.Mirrors are used in making periscopes.
Deviation of Light by a Plane Mirror
When a ray of light is incident on the surface of a plane mirror, it gets reflected with an angle of incidence equal to the angle of reflection. Suppose that the ray continues through the mirror in a straight line, it will make an angle θ with the surface of the mirror. The angle between the straight line path and the reflected ray is two times the angle of incidence. This is called deviation of the light and measures the angle at which the light gets deviated from its straight line path.
Difference Between Virtual and Real Images Formed by Mirrors
In plane mirrors, virtual images are formed. Virtual images are the images that are formed behind the mirror. Light does not actually pass through the location on the other side of the mirror and it appears as if the light is coming from behind the mirror. The image is erect in a plane mirror.
Curved mirrors form real images. These images are formed in front of the mirror. These images are formed when the light passes through the actual image location.
Relation Between Object Distance and Image Distance in Plane Mirrors
There is a relationship between the object distance to the mirror and the image distance to the mirror. In case of plane mirrors, the object distance is equal to the image distance which means that the image is at the same distance behind the mirror as the object is in front of the mirror. For example, if you stand at a distance of 3 meters from a plane mirror, your image will be formed at a distance of 3 meters behind the mirror.
Relative Size of Image and Object in Plane Mirrors
In a plane mirror, the size of the image and the object is the same. For example, if you keep a candle measuring 15 cm in length in front of a plane mirror, you will see an image that is 15 cm tall. The ratio of the size of the image to the size of the object is called magnification. Plane mirrors produce images having a magnification of 1.
Thus, plane mirrors form images with different characteristics. The images formed by the plane are upright, virtual., at the same distance from the mirror as the distance of the object, of the same size, and left and right reversed.
FAQs on Reflection on a Plane Mirror: Explained for Students
1. What is a plane mirror and what type of reflection does it produce?
A plane mirror is a mirror with a flat, reflective surface. When light rays strike this surface, they undergo specular reflection, meaning all parallel incident rays are reflected in a single, parallel direction. This is different from diffuse reflection (from rough surfaces), which scatters light in many directions. This property is what allows a plane mirror to form a clear image.
2. What are the two fundamental laws of reflection?
The two laws of reflection govern how light bounces off any smooth surface, including a plane mirror:
- The First Law: The incident ray, the reflected ray, and the normal (an imaginary line perpendicular to the mirror's surface at the point of incidence) all lie in the same plane.
- The Second Law: The angle of incidence (the angle between the incident ray and the normal) is exactly equal to the angle of reflection (the angle between the reflected ray and the normal).
3. What are the main characteristics of an image formed by a plane mirror?
An image formed by a plane mirror has four key characteristics:
- It is virtual, meaning the light rays do not actually meet to form the image; it cannot be projected onto a screen.
- It is erect or upright, appearing the same way up as the object.
- It is the same size as the object.
- It is laterally inverted, meaning the left side of the object appears as the right side of the image.
4. Why is the image in a plane mirror called a 'virtual' image?
The image is called virtual because it is formed by the apparent intersection of reflected light rays. When you look into a plane mirror, the light from the object reflects off the mirror and enters your eyes. Your brain traces these rays back in straight lines to a point behind the mirror where they seem to originate. Since the light rays do not physically converge at that location, the image is not real and cannot be captured on a physical screen placed there.
5. What is the importance of lateral inversion in real life?
Lateral inversion is the reason why the word 'AMBULANCE' is often written in reverse on the front of emergency vehicles. When drivers see the vehicle in their rearview mirror (which is a plane mirror), the laterally inverted text appears corrected and readable, allowing them to quickly understand the situation and give way.
6. Why is the focal length of a plane mirror considered to be at infinity?
The focal length is the distance at which parallel rays of light converge after reflection. In a plane mirror, parallel rays of light that strike its surface are reflected as parallel rays; they never converge to a single point. Since they meet only at an infinite distance, the focal point is said to be at infinity. Consequently, the focal length of a plane mirror is also infinity.
7. How is the image from a plane mirror different from an image formed by a concave mirror?
A plane mirror always forms a virtual, erect, and same-sized image, regardless of the object's position. In contrast, a concave mirror can form different types of images depending on the object's distance. It can form a real, inverted image (which can be magnified or diminished) when the object is placed beyond its focal point, or a virtual, erect, and magnified image when the object is placed very close to the mirror (within the focal length).
8. What are some common examples of where plane mirrors are used?
Plane mirrors are widely used in daily life due to their ability to produce a clear, undistorted image. Common examples include:
- Dressing mirrors and bathroom mirrors for personal grooming.
- Rear-view and side-view mirrors in vehicles.
- Mirrors used in periscopes to see over obstacles.
- Mirrors in kaleidoscopes to create beautiful patterns through multiple reflections.
- Security mirrors in shops to provide a wide field of view.
