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Concave and Convex Mirrors are the two types of spherical mirrors in Physics. Spherical Mirrors are those mirrors whose reflecting surface is part of a hollow sphere of glass. They are generally made up of glass and are different from plane mirrors.
- Concave Mirrors are spherical mirrors whose reflecting surface is curved inwards.
- Convex Mirrors are mirrors whose reflective surface is curved outwards.
- Concave mirror is known as a ‘Converging Mirror’ while a convex mirror is known as a ‘Diverging Mirror’.
- Concave and Convex Mirrors have a wide variety of applications in our daily lives.
The main difference between concave and convex mirrors is that concave mirrors converge light rays at one point, while convex mirrors diverge the light rays from one common point.
Read More: NCERT Solutions for Class 10 Science Light- Reflection and Refraction
Key Terms: Concave Mirror, Convex Mirror, Spherical Mirror, Reflection, Light, Virtual Image, Real Image, Focal Length, Focus
What is a Mirror?
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A mirror is a reflective surface that bounces off the light to produce either a real or a virtual image.
- The object is the source of the incident rays and the image is formed by the reflected rays.
- On the basis of the intersection of light rays, the images are classified as real or virtual images.
- A real image is formed when the light rays intersect while virtual images are formed when light rays diverge.
- Plane mirror is a flat and smooth reflective surface that always forms a virtual image.
- It means that the image formed is upright, and of the same shape and size as the object.
- A spherical mirror is a mirror whose reflecting surface is part of a hollow sphere of glass.
What are Spherical Mirrors?
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Spherical Mirrors are defined as mirrors that have the shape of a piece cut out of a spherical surface.
- The curved surface has a coating of silver on one side and a polished surface on the other side that is used for reflection.
- The images formed by a spherical mirror can either be real or virtual.
- Spherical Mirrors can be classified into two major types namely Concave Mirrors and Convex Mirrors.
- They are commonly used as reflecting surfaces in day-to-day objects.
Read More: Reflection of Light by Spherical Mirrors
What are Concave Mirrors?
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Concave Mirror is a spherical mirror with its inner surface as the reflecting surface. It is also known as a converging mirror. In concave mirrors, the incident rays strike the mirror's surface in parallel, reflect, and meet at a location called the focal point. The shape of a concave mirror is like a spoon.
Properties of Concave Mirror
- In a concave mirror, light converges at a point where it strikes and reflects back from the mirror’s reflecting surface.
- A magnified, erect and virtual image is obtained when the concave mirror is placed too close to an object.
- When the distance between the object and the mirror is more, the size of the image is reduced, making it a real and inverted image.
- Images formed by the concave mirrors can be small or large and can be real or virtual.
What are Convex Mirrors?
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Convex Mirror is a spherical mirror whose outer surface is a reflecting surface. Convex mirrors are also known as diverging mirrors. In convex mirrors, the incident ray from the same spot reflects off and moves in a different path.
Properties of Convex Mirror
- Images created by convex mirrors are erect, diminished, and focused on the object.
- They are known as diverging mirrors as the light reflecting through the surface diverges in any direction.
- They are used as rear-view mirrors as they can diverge light beams and make virtual images.
Read More: Light- Reflection and Refraction Important Questions
Difference between Concave and Convex Mirror
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Concave and Convex mirrors are both spherical mirrors. A concave mirror converges light rays while a convex mirror diverges light rays. The key difference between concave and convex mirrors is as follows:
| Parameter | Concave Mirror | Convex Mirror |
|---|---|---|
| Meaning | Concave Mirrors have a reflecting curved surface bent inwards which means it faces the center of the sphere. | Convex Mirrors have a reflecting surface curved outwards. |
| Alternate Name | It is also known as Converging Mirror. | It is also known as Diverging Mirror. |
| Structure | The mirror coating of concave mirror is on the outer side of the spherical surface. | The mirror coating of a convex mirror is on the inner side of the spherical surface. |
| Centre of Curvature and Reflecting Surface | The center of curvature and the reflecting surface fall on the same side of the mirror. | The center of curvature and the reflecting surface fall on the opposite side of the mirror. |
| Focus | The focus lies in front of the mirror and the focal length is negative. | The focus lies behind the mirror and the focal length is positive. |
| Properties of Image | The image formed is real, inverted, and enlarged (except when the object is between P and F where the image is virtual, erect, and enlarged). | The image formed is virtual, erect, and diminished. |
| Image Projection | The image can be projected on a screen as they are real in nature. | Images cannot be projected on a screen as they are virtual. |
| Usage | They are used in reflecting telescopes, shaving mirrors, torchlights, etc. as they give a magnified image of objects. | They are used as side views or rearview mirrors in vehicles as they cover a wider area of view. |
Image Formation by Spherical Mirrors
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Spherical Mirrors lead to the formation of images when light rays fall on their surface. Some guidelines for rays falling on Concave and Convex Mirrors are listed below:
- When a ray strikes a concave or convex mirror at the pole, it is reflected making the same angle with the principal axis.
- When a ray parallel to the principal axis strikes a concave or convex mirror, the reflected ray passes through the focus.
- When a ray passing through focus strikes concave or convex mirrors, the reflected ray will be parallel to the principal axis.
- A ray passing through the center of curvature will retrace its path after reflection.
Image Formation By Concave Mirror
The image formation by concave mirrors can be summarized as follows:
| Position of the Object | Position of Image Formation | Nature and Size of Image |
|---|---|---|
| Infinity | At the Focus (F) | Real and inverted image; smaller than the Object. |
| Behind the Center of Curvature | Between the Center of Curvature and Focus | Real image; smaller than Object |
| At the Center of Curvature and Focus | At the Center of Curvature | Real image; same size as the Object. |
| In between the Center of Curvature and Focus | Behind the Center of Curvature | Real image; larger than the Object. |
| At Focus | At Infinity | Real image; much larger than the Object. |
| In between Focus and Pole | - | Virtual and erect image; larger than the Object. |
Image Formation By Convex Mirror
The image formation by convex mirrors is as follows:
| Position of Object | Position of Image | Nature and Size of Image |
|---|---|---|
| At Infinity | At the Focus F, behind the Mirror | Virtual and Erect; Highly diminished |
| Between Infinity and the Pole | Between P and F, behind the Mirror | Virtual and Erect; Diminished |
Uses of Concave and Convex Mirrors
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Concave and Convex Mirrors have a wide variety of applications in our daily lives. Some important applications of Concave and Convex Mirrors are as follows:
Uses of Convex Mirrors
- Convex mirrors are used as rear-view mirrors in vehicles as they can diverge light beams and create virtual images.
- They are used inside the buildings so that people can see all around the building at once.
- They are used to make magnifying glasses by placing two convex mirrors back to back.
- They are also used for several security purposes in many places and devices.
- Convex mirrors are used in ATMs to check whether someone is behind a person or not.
- They are also used as streetlight reflectors as they can spread light over bigger areas.
Uses of Concave Mirrors
- Concave mirrors are the most effective reflectors and are used in torchlights, railway engines, motor vehicles, and headlights.
- They are used in shaving mirrors as they have reflective and curved surfaces.
- They are also used in ophthalmoscopes.
- Concave mirrors are used in making astronomical telescopes.
- They are used in the headlights of motor vehicles as reflectors.
- They are also used to focus the sunlight to produce heat in the solar furnace.
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Things to Remember
- Spherical Mirrors are mirrors that are made from a part of a hollow sphere.
- Concave Mirrors and Convex Mirrors are the two types of Spherical Mirrors.
- Concave Mirror is a spherical mirror whose reflecting surface is curved inwards.
- Convex Mirror is a spherical mirror whose reflecting surface is curved outwards.
- Concave mirrors are converging mirrors and Convex mirrors are diverging mirrors.
- In concave mirrors, the image formed is real, inverted, and enlarged.
- In convex mirrors, the image formed is virtual, erect, and diminished.
- Concave Mirrors are used in telescopes, shaving mirrors, torchlights, etc. as they give a magnified image of objects.
- Convex Mirrors are used as side view or rearview mirrors in vehicles as they cover a wider area of view.
Sample Questions
Ques. What are the types of Spherical Mirrors? (3 Marks)
Ans. There are two main types of spherical mirrors which are Concave Mirrors and Convex Mirrors.
- Concave Mirror: When the reflective surface is on the side curved inwards, a mirror is referred to as a concave mirror. In concave mirrors, light converges at a point where it strikes and reflects back.
- Convex Mirror: When the reflective surface is curved outwards, a mirror is classified as a convex mirror. In convex mirrors, the light reflecting through the surface diverges in any direction.
Ques. Give one major difference between concave and convex mirrors. (1 Mark)
Ans. Concave mirrors are converging mirrors that converge light rays at one point, while convex mirrors are diverging mirrors that diverge the light rays from one common point.
Ques. What is Mirror Formula? (3 Marks)
Ans. The mirror formula is given as
\(\frac{1}{f} = \frac{1}{v} + \frac{1}{u}\)
Where
- f is the focal length of the mirror.
- v is the distance of the image.
- u is the object distance.
Ques. What are the applications of a Concave Mirror? (2 Marks)
Ans. Concave mirrors help in the inward reflection of light to the focal point. Concave mirrors can also be used for a variety of purposes, including:
- Head Mirrors
- Shaving Mirrors
- Astronomical Telescopes
- Headlights
- Solar Furnace
- Ophthalmoscope
Ques. Which kind of mirrors are used in the headlights of a motor car and why? (1 Mark)
Ans. A concave mirror is used in the headlights of a motor car to get a parallel beam of light.
Ques. What is the minimum number of rays required for locating the image formed by a concave mirror for an object? Draw a ray diagram to show the formation of a virtual image by a concave mirror. (2 Marks)
Ans. A minimum of two rays are required to create the image formed by a concave mirror for an object.
The ray diagram for the formation of a virtual image by a concave mirror is as follows:
Ques. List the properties of the image formed by a convex mirror. (3 Marks)
Ans. The properties of the image formed by a convex mirror are:
- The image is formed behind the mirror, between the pole and its focus.
- It is virtual and erect.
- The size of the image is always smaller than the object.
- Magnification is always positive.
Ques. List the properties of the image formed by a concave mirror, when object is placed between the focus and pole of the mirror. (3 Marks)
Ans. The properties of the image formed by a concave mirror when the object is placed between the focus and pole of the mirror:
- The image is formed behind the mirror.
- It is enlarged and magnified.
- It is virtual and erect.
Ques. State the type of mirror preferred in
(i) Rear-view mirror in Vehicles
(ii) Shaving Mirrors
Justify your answer in each case. (3 Marks)
Ans. (i) Convex Mirror. A convex mirror is used as a rearview mirror because it gives a wider view as it is curved outwards. It also produces erect and diminished images of the traffic behind the vehicle.
(ii) Concave Mirror. A concave mirror is used as a shaving mirror to see a large size image of the face. When the object lies in between the pole and the principal focus of a concave mirror, it forms a virtual, erect, and enlarged image behind it.
Ques. State the applications of Convex Mirrors. (2 Marks)
Ans. Convex Mirrors give a wider view of the object. Some of the applications of convex mirrors are as follows:
- For Security Purposes
- Vehicle Mirrors
- In Parking Lots
- Street Light reflectors
- Magnifying glasses
- In ATMs
Ques. Explain the image formation in Concave and Convex Mirrors. (3 Marks)
Ans. A concave mirror is a converging mirror which means when the light falls on the mirror, the light reflected from the source is in the inward direction. Therefore, the image formed is in front of the mirror in the case of concave mirrors.
A convex mirror is divergent, thus, when the light falls on the mirror, the light reflected from the source is in the outward direction. Therefore, the image formed is behind the mirror in convex mirrors.
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