• Spherical mirrors are the mirror with shape of a piece cut out from a sphere. Depending upon the reflecting surface a spherical mirror can be of two types i.e., concave mirror and convex mirror.
• In a concave mirror the bent in surface is the reflecting surface. As concave mirrors form a magnified image of objects kept close to them, they are used as make up mirrors and shaving mirrors. In a convex mirror the bulged out surface is the reflecting surface. As convex mirrors provide a wider field view, they are used as rear view mirrors in cars and other vehicles.
• A set of rules for image formation is followed in order to draw the images for different positions of object placed in front of a spherical mirror.
• The nature of image formed in case of a concave mirror, varies in accordance with the position of the object.
• The nature of image formed in case of a convex mirror is always diminished, virtual and erect. In order to measure the distances and size of object and image, either conventional or modern sign conventions can be used.
• Mirror formula is defined as the relationship between the image distance, object distance and the focal length of a spherical mirror.
Mathematically, it is given as
where u is the object distance, v is the image distance and f is the focal length of the mirror.
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An object is placed at the centre of curvature of a convex mirror. Its image will be formedMarks:1
behind the mirror.
A convex mirror always forms virtual and erect image behind it irrespective of the object distance.
The type of mirror used in solar furnace isMarks:1
Light rays from the sun converge at the focus of a concave mirror after reflection, which is not possible for any other kind of mirror. This enables us to attain high intensity of heat at its focus, which can be used to heat things. Thus, solar furnace uses concave mirror.
A concave mirror forms a real image of an object. The image would beMarks:1
inverted and on the same side as the object.
Since the image formed by the concave mirror is real, it must be inverted. Besides, a concave mirror always forms real images on the same side as the object. This can be concluded from the fact that actual light rays can never meet behind the mirror to form a real image.
For rear view mirror in vehicles, we preferably useMarks:1
A convex mirror always forms diminished and virtual images. Therefore, the field of view is large. Hence, it is used as rear view mirror in the vehicles.
Linear magnification of a real image in spherical mirror isMarks:1
Linear magnification is defined as the ratio of the height of image to the height of an object. Whenever there is a real image, it is always inverted and for an inverted image, height of image is negative and therefore magnification is also negative.