In this Physics video for Class 10 in Hindi we explained image formation in a spherical mirror happen. Spherical mirrors are of two types, viz., concave spherical mirror and convex spherical mirror. We also explained what pole, centre of curvature, principal axis, principal focus, radius of curvature and focal length are. Image by spherical mirrors are of two types, viz., real image and virtual image. When image can be cast on a screen, it is called the real image. When image can not be cast on a screen, but seen through a mirror, it is called the virtual image.
In order to locate the image of an object, an arbitrarily large number of rays emanating from a point could be considered. However, it is more convenient to consider only two rays, for the sake of clarity of the ray diagram. These rays are so chosen that it is easy to know their directions after reflection from the mirror. The intersection of at least two reflected rays give the position of image of the point object. Any two of the following rays can be considered for locating the image.
(i) A ray parallel to the principal axis, after reflection, will pass through the principal focus in case of a concave mirror or appear to diverge from the principal focus in case of a convex mirror.
(ii) A ray passing through the principal focus of a concave mirror or a ray which is directed towards the principal focus of a convex mirror, after reflection, will emerge parallel to the principal axis.
(iii) A ray passing through the centre of curvature of a concave mirror or directed in the direction of the centre of curvature of a convex mirror, after reflection, is reflected back along the same path. The light rays come back along the same path because the incident rays fall on the mirror along the normal to the reflecting surface.
(iv) A ray incident obliquely to the principal axis, towards a point P (pole of the mirror), on the concave mirror or a convex
mirror, is reflected obliquely. The incident and reflected rays follow the laws of reflection at the point of incidence (the pole), making equal angles with the principal axis.
Image formation by concave mirror :-
1) When object is at infinity, a point-sized real image is formed at the focus.
2) When object is beyond the centre of curvature, a diminished, real and inverted image is formed between the focus and the centre of curvature.
3) When object is at the centre of curvature, a same sized, real and inverted image is at the centre of curvature.
4) When object is in between the focus and the centre of curvature, an enlarged, real and inverted image is formed beyond the centre of curvature.
5) When object is at the focus, an highly enlarged, real and inverted image is formed at infinity.
6) When object is in between the pole and the centre of curvature, an enlarged, virtual and erect image is formed behind the mirror.
Uses of concave mirrors :-
1) in torches, search-lights and vehicles headlights to get powerful parallel beams of light.
2) as shaving mirrors to see a larger image of the face.
3) dentists use these mirrors to see large images of the teeth of patients.
4) used to concentrate sunlight to produce heat in solar furnaces.
Image formation by concvex mirror :-
1) When object is at infinity, a point-sized, virtual image is formed at the focus.
2) When object is in between infinity and the pole, a diminished, virtual and erect image is formed beyond the mirror.
Use of convex mirrors :-
These are commonly used as rear-view mirrors in vehicles enabling the driver to see traffic behind him/her. These mirrors are preferred because they always give an erect, though diminished, image. Also, they have a wider field of view.
Pole : It is the centre of the reflecting surface.
Aperture : It is the diameter of the circular boundary of a spherical mirror.
Centre of curvature : It is the centre of the sphere of which the mirror is a part of.
Principal axis : It is the straight line joining the pole and the centre of curvature.
Radius of curvature : It is the distance of the centre of curvature from the pole of the spherical mirror.
Principal focus : It is the point where the rays parallel to the principal axis converges or appears to diverge from after reflecting from the spherical mirror.
Focal length : It is the distance of the focus from the pole of the spherical mirror.
This is a topic of Chapter 10 - 'Light - Reflection and Refraction' from NCERT for Class 10.
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🔴 Click here to watch the whole playlist on Chapter 10 : 'Light - Reflection and Refraction' for Class 10 :
• Light - Reflection and...
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🔴 Light - Reflection and Refraction (Introduction)
• Light - Reflection and...
🔴 Spherical Mirrors (Introduction)
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23 авг 2021
