What is the sign of the object -distance u when an object is placed before a concave mirror ?

When an object is said to be a particle ?

What is the type of nature of image formed for an object placed an axis of concave mirror between pole & centre?

When an object is said to be in motion ?

A plano convex lens of refractive index 1.5 and radius of curvature 30cm. Is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of size of the object.

A real image obtained by a concave mirror is 4 times bigger than the object. If the object is displaced by 3 cm away from the mirror, the image size becomes 3 times the object size. Find the focal length of the mirror.

For normal eye vision what is the object distance and image-distance when the object is placed at a near point? (Take the distance between the eye lens and the retina as 2.3 cm.)

For normal eye vision what is the object distance and image-distance when the object is placed at a far point? (Take the distance between the eye lens and the retina as 2.3 cm.)

If x and y denote the distance of the object and image from the focus of a concave mirror . The line y=4x cuts the graph at a point whose abscissa is 20 cm. The focal length of the mirror is

{:("Column I","Column II"),((A)" An object is placed at a distance equal to focal length from pole before convex mirror",(p)" Magnification is "(infty)),((B)" An object is placed at focus before a concave mirror",(q)" Magnification is (0.5)"),((C) "An object is placed at the centre of curvature before a concave mirror" , (r) "Magnification is (1//3)") , ((D) " An object is placed at a distance equal to radius of curvature before a convex mirror" , (s) "Magnification is (-1)"):}