If the radius of curvature of a spherical mirror is $30 \ cm$,what is its focal length (in $cm$)?

$A$ convex lens has a focal length of $25\, cm$. Calculate the distance of the object from the lens if the image is to be formed on the opposite side of the lens at a distance of $75\, cm$ from the lens. What will be the nature of the image?

The focal length of a plane mirror is $.....$

What are the advantages and disadvantages of using a convex mirror for seeing traffic at the rear?

Which of the following can produce a magnification of $+5$ as well as $-5$?

Where should an object be placed so that a real and inverted image of the same size is obtained by a convex lens?