An object is placed in front of a concave mirror of focal length $15 \ cm$. The image formed is twice the size of the object. If the image is virtual,the position of the object is at ...... $cm$.

The primary purpose of using a parabolic mirror in a reflecting telescope is

$A$ short straight object of length $l$ lies along the central axis of a spherical concave mirror,at a distance $X$ from the mirror. The focal length of the mirror is $F$. If the length of the image in the mirror is $l^{\prime}$,then the ratio $\left(\frac{l^{\prime}}{l}\right)$ is (assume $l << X$ and $l << F$):

An object is placed at the principal focus of a convex mirror. The image will be at

Define the focal plane of a concave mirror.

$A$ spherical mirror is obtained as shown in the figure from a hollow glass sphere. If an object is positioned in front of the mirror,what will be the nature and magnification of the image of the object? (Figure drawn as schematic and not to scale)