$A$ double convex lens has a focal length of $25\; cm$. The radius of curvature of one of the surfaces is double the other. Find the radii if the refractive index of the material of the lens is $1.5$.

When will the convergent nature of a convex lens be less as compared to its nature in air?

An object approaches a convergent lens from the left of the lens with a uniform speed $5 \, m/s$ and stops at the focus. The image:

Given below are two statements:
Statement $(I)$: When an object is placed at the centre of curvature of a concave lens,the image is formed at the centre of curvature of the lens on the other side.
Statement $(II)$: $A$ concave lens always forms a virtual and erect image.
In the light of the above statements,choose the correct answer from the options given below:

$A$ screen is placed $90\, cm$ from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by $20\, cm$. The focal length of the lens is.....$ cm$

$A$ convex lens of focal length $0.15 \,m$ is made of a material of refractive index $\frac{3}{2}$. When it is placed in a liquid, its focal length is increased by $0.225 \,m$. The refractive index of the liquid is