Image Formation by Concave Mirrors

Sign Convention for Spherical Mirrors

• Distances parallel to the principal axis are measured from the pole (P) of the mirror.
• Negative sign indicates distance measured in the direction opposite to the incident ray, while positive sign indicates distance measured in the direction of the incident ray.
• Distance below the axis is negative, while distance above is positive.
• Focal length (f) is positive for a concave mirror and negative for a convex mirror.

Magnification of Spherical Mirrors

• Magnification (m) is given by m = hi/uo = -ho/u, where hi is the height of the image and ho is the height of the object.
• Height of the object is taken as positive, as it is usually placed above the principal axis.
• Height of the image is taken as positive for virtual images and negative for real images.

Image Formation by Convex Mirrors

• Image formation by a convex mirror can be understood through ray diagrams for two positions of the object: at infinity and at a finite distance from the mirror.
• Results are summarized in Table 2, showing nature, position, and relative size of the image formed by a convex mirror.

Mirror Formula and Magnification

• Mirror formula: 1/v + 1/u = 1/f, relating object distance (u), image distance (v), and focal length (f).
• Formula is valid for all spherical mirrors and all positions of the object.

Image Formation by Concave Mirrors

• Image formation by a concave mirror depends on the position of the object in relation to points P, F, and C.
• Nature, position, and size of the image formed by a concave mirror vary depending on the object's position.
• Image is real for some positions of the object and virtual for others.
• Image is either magnified, reduced, or has the same size, depending on the object's position.

Uses of Concave Mirrors

• Concave mirrors are used in torches, search-lights, and vehicles' headlights to produce powerful parallel beams of light.