A flat mirror is just a perfectly planar, smooth, mirrored surface. The image created here is not altered in any way. On the other hand, a spherical mirror has a uniform curvature and a constant radius of curvature and can have distorted images.
Depending on which side you place the reflected surface on, spherical mirrors can be convex or concave.
A concave mirror, also known as a converging mirror, is a mirror that is turned inwards in the centre. When a hollow sphere is sliced in a certain half, and the exterior surface of that portion is polished, it becomes a mirror, with the interior surface as the reflecting side. They are known as converging mirrors because the incident light is converged and reflected inwardly due to their shape.
Concave mirrors, unlike flat mirrors, can project real images in front of the mirror at the point where the light focuses. The rule of reflection still applies to concave mirrors, but because the mirror’s surface is curved, the angle at which light strikes it varies depending on which section of the mirror the light strikes. This allows concave mirrors to concentrate light at a point.
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|Concave Mirrors Have the Following Characteristics|
|Concave Mirror Image Formation|
|Image Formation Table of a Concave Mirror|
Concave Mirrors Have the Following Characteristics
- Can focus Light on a Single Point: Depending on which part of the mirror is illuminated, the angle at which light reaches the curved surface changes. As a result, concave mirrors can concentrate light into a single point.
- Can form both Virtual and Real Images: Unlike a plane mirror, concave mirrors can produce both sorts of images. Real images are formed when the object is more than one focal length distant from the mirror, and a virtual image is formed if the object is less than one focal length away from the concave mirror.
- Images formed can be both Enlarged or Shrunken: When the object’s distance from the concave mirror decreases, the image’s size increases, and when the distance is increased, the image’s size decreases.
Also See: CBSE Class 10 Syllabus
Concave Mirror Image Formation
The generation of an image is determined by the object’s location concerning the concave mirror.
A mirror is made up of the following components:
- Pole: Is the centre of the reflecting surface of a spherical mirror denoted by P.
- Principal Axis: It is the straight line that passes through the pole.
- Centre of Curvature: Centre of the sphere is used to form the concave mirror.
- Focus: The focal point is the common point on the principal axis on which the reflected rays converge when coming in parallel to the principal axis denoted by F.
- Focal Length: The distance between its pole and its Focus is represented by f.
We take two incident rays from the object into account. After reflection, the intersection of these two rays yields the position and attributes of the object’s image:
- When the object is positioned between the Focus and the Pole:-
One ray runs parallel to the main axis, while the other passes via the mirror’s centre of curvature.
The image created here is virtual, upright, and magnified.
- When the object is positioned at Focus:-
One ray is parallel to the main axis, while the other passes via the mirror’s centre of curvature.
The image formed here is inverted, real and highly magnified.
The image is formed at infinity.
- When the object is positioned between the centre of curvature and focus:-
One ray is parallel to the main axis, while the other passes through the concave mirror’s main focus.
The image formed here is inverted, real and comparatively enlarged.
The image is formed beyond the centre of curvature.
- When the object is positioned at the centre of curvature:-
One ray emerges from the object parallel to the primary axis, while the other passes through the mirror’s focus.
The image formed is inverted, real, and the same size as the object.
The image is formed in the same position as the object.
- When the object is positioned beyond the centre of curvature:-
One is parallel to the main axis, while the other is aimed at the mirror’s centre of curvature.
The image formed is inverted, real and shrunken.
- When the object is positioned at Infinity:-
Both rays emerge parallel to the principal axis and converge to the focus after reflection.
The image formed is inverted, real and shrunken (point size).
The image is formed at the Focus.
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Image Formation Table of a Concave Mirror
|Position of the object||Position of the image||Size of the image||Nature of the image|
|Between F and P||Behind the mirror||Enlarged||Upright and virtual|
|At F||At infinity||Highly enlarged||Inverted and Real|
|Between C and F||Beyond C||Enlarged||Inverted and Real|
|At C||At C||Same size||Inverted and Real|
|Beyond C||Between F and C||Diminished||Inverted and Real|
|At infinity||At focus, F||Shrunken(Point Size)||Inverted and Real|
NOTE: Except when an object is positioned between the focus and the pole of the mirror, a concave mirror always forms real and inverted images.
We need to calculate some fundamental parameters numerically to learn more about the formation of images through a concave mirror.
- Object distance from the mirror (u)
- Image distance from the mirror (v)
- Object height from the principal axis
- Image height from the principal axis
- And the Focal Length (f)
However, determine whether these quantities are positive (distances measured horizontally to the right of the pole or vertically above the principal axis) or negative (distances measured horizontally to the left of the pole or vertically below the principal axis).
This is done according to a set of guidelines called Sign Conventions:-
As a result, the following values are always assessed in this manner for a concave mirror:-
- The object distance is always negative since the object is always to the left of the pole.
- The object height is always positive since the object is always above the principal axis.
- The focal length is always negative since the focus is always to the left of the pole.
- The image distance is always negative for a real picture and always positive for a virtual image.
- The image height is positive or negative, depending on the picture being created above or below the principal axis.
When an object is placed u units in front of a spherical mirror with a focal length of f units and the image is created v units away from the mirror, Mirror Formula relates u, v, and f as follows:
1/u + 1/v = 1/f
Sign varies as per the sign conventions.
A concave mirror has the centre bent inwards. Concave mirrors, unlike plane mirrors, can generate both virtual and real images.
A pole, Centre of curvature, Principal axis, and focus form up a mirror.
When the object is more than one focal length away from the concave mirror, a real image is generated, and when the object is less than one focal length away from the mirror, a virtual image is formed. The image’s size increases as the distance between it and the concave mirror reduces, while the object’s size is reduced as the distance increases. The size of an image grows as its distance from the concave mirror decreases.
Mirror Formula relates u, v, and f when the object is positioned u units in front of a spherical mirror with a focal length of f units, and the image is formed v units distant from the mirror:
1/f = 1/u + 1/v. If you want to learn more about the topic, then Lakhmir Singh provides a wealth of information on this topic; login here.
If you are preparing for CBSE Class 10 Term 2 exams, then go through these:
1. What type of mirror is a Concave Mirror? Why is it also called a converging mirror?
A concave mirror is a type of mirror that has the centre tilted inwards. When a hollow spherical glass is divided in half, and the external surface of that half is polished, the internal surface becomes the reflective side. Because of their form, incident light converges and is reflected inwards. Hence they are known as converging mirrors.
2. What kind of images are formed through a concave mirror?
Concave mirrors can produce both actual and virtual images. The rule of reflection still applies to concave mirrors, but because the surface is curved, the angle at which light strikes it varies depending on which part of the mirror it strikes. This also allows the concave mirror to focus light on a single spot. The warped images may be enlarged, downsized, inverted, or erect.
3. In a concave mirror, how are both magnified and shrunken images formed?
The image’s size grows as the object’s distance from the concave mirror lowers and decreases as the distance increases. This is how a concave mirror can produce magnified and diminished images.
4. What are the constituents of a mirror?
The following components form a mirror:
Pole is the centre of a spherical mirror reflecting surface, and the straight line that runs through the pole is known as the Principal axis.
The concave mirror’s centre of curvature is the centre of the sphere glass used to make it. The common point on the principal axis on which the reflected rays converge when coming in parallel to the principal axis is called the focus.
Focal length is the distance between the mirror’s pole and its focus.
5. How is an image analyzed in a concave mirror?
The object’s location determines the formation of an image with respect to the mirror. Two incident rays from the object are taken into consideration. The location of the image is determined by the intersection of these two rays after reflection, as are the image’s properties.
6. What are sign conventions, and why are they important?
The Sign Convention is a set of guidelines for setting signs for image and object distance or height and focal length for numerical evaluations during image formation. The concave mirror’s sign conventions are based on the fact that the objects are either on the left or right side of the pole or above or below the principal axis.
7. What is a Mirror Formula?
The Mirror formula provides a relation between the focal length, object distance from the mirror, and image distance from the mirror and can be used to evaluate any of these.
It’s given as 1/u+1/v=1/f where,
u is the distance of the object from the mirror,
v is the distance of the image from the mirror and,
f is the focal length.
The values of these measures should be assessed in accordance with the sign conventions.