Using the mirror formula, 1/f = 1/v + 1/u. Here, v = -15 cm (real image) and u = -30 cm (object distance). Thus, 1/f = 1/(-15) + 1/(-30) = -1/10, so f = -10 cm.

Using the mirror formula, 1/f = 1/v + 1/u. Here, v = -15 cm (image distance is negative for concave mirror) and u = -30 cm. Therefore, 1/f = 1/(-15) + 1/(-30) = -1/10. Thus, f = 10 cm.

Magnification (m) = -v/u. Here, v = -5 cm and u = -10 cm, so m = -(-5)/(-10) = 2.

When the object is placed at the focus of a concave mirror, the image is formed at infinity, leading to infinite magnification.

When the object is placed between the focal point and the mirror, the image formed is virtual and erect.

When the object is placed beyond 2F, the image formed by a convex lens is real, inverted, and diminished.

When the object is placed beyond 2F, the image formed by a convex lens is real, inverted, and smaller than the object.

A convex lens is used to correct hypermetropia (farsightedness) as it converges light rays before they enter the eye.

When the object is placed between the focal point and the mirror, the image formed by a concave mirror is virtual and erect.

The critical angle is defined as the angle of incidence above which total internal reflection occurs, and it is always less than 90 degrees.

The image formed by a plane mirror is virtual, erect, and located behind the mirror at the same distance as the object.

A concave lens diverges light rays, and it has a negative focal length.

A convex mirror always forms virtual images and has a negative focal length.

A plane mirror always forms a virtual image that is the same size as the object and is erect.

A concave lens always forms a virtual image that cannot be projected on a screen; hence, a real image cannot be formed.