$A$ thin glass (refractive index $1.5$) lens has an optical power of $-5\,D$ in air. Its optical power in a liquid medium with a refractive index of $1.6$ will be: (in $,D$)

$A$ convex lens forms a real image of an object for its two different positions on a screen. If the height of the image in both cases is $8 \ cm$ and $2 \ cm$,then the height of the object is ........ $cm$.

$A$ thin equiconvex lens is made of glass of refractive index $1.5$ and its focal length is $0.2 \ m$. If it acts as a concave lens of $0.5 \ m$ focal length when dipped in a liquid,the refractive index of the liquid is:

$A$ convex lens of focal length $f$ produces a real image $n$ times the size of the object. The image distance is

$A$ point object is placed on the axis of a thin convex lens of focal length $0.05 \ m$ at a distance of $0.2 \ m$ from the lens and its image is formed on the axis. If the object is now made to oscillate along the axis with a small amplitude of $A \ cm,$ then what is the amplitude of oscillation of the image? [You may assume $\frac{1}{1+x} \approx 1-x,$ where $x << 1$]

The power of a biconvex lens is $10 \; D$ and the radius of curvature of each surface is $10 \; cm$. The refractive index of the material of the lens is: