Simple microscope is used to see the object first in blue light and then a red light. Due to the change from blue to red light, its magnifying power

Concave and convex lenses are placed touching each other. The ratio of magnitudes of their power is $2: 3$. The focal length of the system is 30 cm . The focal lengths of individual lens are

An astronomical telescope has a large aperture to

Three immiscible transparent liquids with uniform refractive indices $\frac{3}{2}, \frac{4}{3}$ and $\frac{6}{5}$ are arranged one on top of another. The depths of the liquids are 3 cm 4 cm and 6 cm respectively. The apparent depth of the vessel is