$A$ plano-convex lens is made of material having refractive index $1.5$. The radius of curvature of the curved surface is $60 \ cm$. The focal length of the lens is . . . . . . $cm$.

$A$ double convex lens of glass of $\mu = 1.5$ has a radius of curvature of each of its surfaces equal to $0.2 \ m$. The power of the lens is:

Focal length of a convex lens is $20 \ cm$ and its refractive index is $1.5$. It produces an erect,enlarged image if the distance of the object from the lens is: (in $cm$)

Sunlight of intensity $1.3 \text{ kW m}^{-2}$ is incident normally on a thin convex lens of focal length $20 \text{ cm}$. Ignore the energy loss of light due to the lens and assume that the lens aperture size is much smaller than its focal length. The average intensity of light,in $\text{kW m}^{-2}$,at a distance $22 \text{ cm}$ from the lens on the other side is. . . . .

$A$ convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens material. Then its focal length will

Remote sensing satellites move in an orbit that is at an average height of about $500 \, km$ from the surface of the earth. The camera onboard one such satellite has a screen of area $A$ on which the images captured by it are formed. If the focal length of the camera lens is $50 \, cm$,then the terrestrial area that can be observed from the satellite is close to ............... $A$.