An equiconvex lens has a power of $2 \ D$. If it is made of glass of refractive index $1.25,$ then the radius of curvature of each of its surfaces will be $.... \ cm$.

In a concave lens, a ray of light emanating from the object parallel to the principal axis of the lens, after refraction:

$A$ hollow lens is made of thin glass and in the shape of a double concave lens. It can be filled with air,water of refractive index $1.33$,or $CS_2$ of refractive index $1.6$. It will act as a diverging lens,if it is

The refractive index of a glass convex lens is $1.5$. The radius of curvature of each of the two surfaces of the lens is $40 \ cm$. The ratio of the power of the lens when immersed in a liquid of refractive index $1.25$ to that when placed in air is:

Assertion: Goggles have zero power.
Reason: Radius of curvature of both sides of the lens is same.

$A$ convex lens forms a real image of a point object placed on its principal axis. If the upper half of the lens is painted black,the image will