The relation between $n_1$ and $n_2$,if the behavior of light rays is as shown in the figure,is:

$A$ lens of refractive index '$\mu$' has focal length '$f$'. When the lens is immersed in a liquid of refractive index '$\mu_0$',its focal length becomes '$f_0$'. Then '$f_0$' is given by

The focal length of a convex lens is $30 \ cm$ and the size of the image is a quarter of the object,then the object distance is ........ $cm$.

$A$ student measures the focal length of a convex lens by obtaining an image of an object pin at a distance '$v$' from the lens,with the object placed at a distance '$u$' from the lens. What will the graph between '$u$' and '$v$' look like?

When blue light is used instead of red light in a convex lens,its focal length will ......... .

The ratio of the focal lengths of a convex lens when kept in air and when it is immersed in a liquid is $1: 2$. If the refractive index of the material of the lens is $1.5$,then the refractive index of the liquid is