Ray optics practice · Mixed difficulty

A convex glass lens $\left( {{\mu _g} = 1.5} \right)$ has a focal length of 8 cm when placed in air. What is the focal length of the lens when it is immersed in water $\left( {{\mu _g} = \frac{4}{3}} \right)$

An air bubble in glass slab $(\mu=1.5)$ when viewed from one side, appears to be at 6 cm and from opposite side 4 cm. The thickness of glass slab is:

A farsighted person cannot focus distinctly objects closer than 100cm. The lens that will permit him to read from a distance of 50 cm, will have a focal length:

An object is puts at a distance of $\mathrm{5 cm}$ from the first focus of a convex lens of focal length $\mathrm{10 cm}$. If a real image is formed, its distance from the lens will be

A step index fibre has a relative refractive index of 0.88%. What is the critical angle at the corecladding interface

A convex lens and a concave lens, each having the same focal length of 10 cm, are put in contact to form a combination of lenses. The power of the combination is

Two converging lens have focal length $f=10 \mathrm{~cm}$ and $f^{\prime}=20 \mathrm{~cm}$ respectively. The optical axes of the lenses coincide. This lens system is used to form an image of an object kept at a certain distance from the first lens. If the size of the final image does not depend on the distance of the object from the first lens. What is the distance (in $\mathrm{cm}$) between the two lens?

Assertion: The cloud in sky generally appear to be whitish.

Reason: Diffraction due to cloud is efficient in equal measure at all wavelengths.

The communication using optical fibres is based on the principle of