The focal lengths of a converging lens are $f_V$ and $f_R$ for violet and red light,respectively. Which of the following relations is correct?

When a plane wavefront is incident on a convex lens,the emerging wavefront becomes . . . . . . .

$A$ lens which has a focal length of $4 \; cm$ and a refractive index of $1.4$ is immersed in a liquid of refractive index $1.6$. What will be the new focal length in $cm$?

$A$ concave lens (refractive index $n_l = 1.5$) has both surfaces of the same radius of curvature $R$. If it is immersed in a liquid of refractive index $n_m = 1.75$,it will act as a:

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 ............... $A$.

$A$ turnip sits before a thin converging lens,outside the focal point of the lens. The lens is filled with a transparent gel so that it is flexible; by squeezing its ends toward its center [as indicated in figure $(a)$],you can change the curvature of its front and rear sides. What happens to the lateral height of the image?