Early Sunrise Late Sunset

Q. Light guidance in an optical fibre can be understood by considering a structure comprising of thin solid glass cylinder of refractive index $n_1$ surrounded by a medium of lower refractive index $n_2$.
The light guidance in the structure takes place due to successive total internal reflections at the interface of the media $n_1$ and $n_2$ as shown in the figure. All rays with the angle of incidence $\text{i}$ less than a particular value ${\text{i}}_m$ are confined in the medium of refractive index $n_1$. The numerical aperture (NA) of the structure is defined as $\sin {\text{i}}_m$.
For two structures namely $S_1$ with $n_1=\sqrt{45}/4$ and $n_2=3/2$, and $S_2$ with $n_1=8/5$ and $n_2=7/5$ and
taking the refractive index of water to be $4/3$ and that of air to be $1$, the correct option(s) is(are)

1. NA of $S_1$ immersed in water is the same as that of $S_2$ immersed in a liquid of refractive index $\frac{16}{3\sqrt{15}}$
2. NA of $S_1$ immersed in liquid of refractive index $\frac{6}{\sqrt{15}}$ is the same as that of $S_2$ immersed in water.
3. NA of $S_1$ placed in air is the same as that of $S_2$ immersed in liquid of refractive index $\frac{4}{\sqrt{15}}$.
4. NA of $S_1$ placed in air is the same as that of $S_2$ placed in water

Q. Why does bluish colour predominate in a clear sky?

Q. We know that the sky is blue because blue light is scattered more than other colors because it has a short wavelength. And the red-orange-yellow during the sunrise & sunset, since light has to travel a larger distance so we see these colours since they are scattered the least. But why does the sky not appear green between sunrise and sunset? We see all the colours of the VIBGYOR spectrum, but never green. Why isnt the distance between Sun and Earth never optimum for us to see a Green Sky?

Q. Mirage is an example of :

1. Reflection of light & Refraction of light
2. Dispersion of light
3. Total Internal Reflection of light only
4. Refraction of light & Total Internal Reflection of light

Q. at atime the image of a sun formed due to reflection at air water interface is found to be highly polarized.if the refractive index of water is μ=4/3 then the angle of sun above horizon

Q. The mirage in desert is caused because :

1. the refractive index of atmosphere does not change with height
2. none of the above
3. there is effect of height on refractive index
4. light is reflected by the sand particles

Q. Explain why, when the sun is overhead at noon, it appears white, but when the same sun is near the horizon at sunset, it appears red.

Q. What is the cause of mirage in desert area ?

Q. The transparent media of refractive indices 1.2, $n$, $n^{{}^{\prime }}$ respectively, are stacked as shown. A ray of light follows the path shown. Then,

1. $n<1.2$
2. $n^{{}^{\prime }}<n$
3. $n^{{}^{\prime }}=1.2n$
4. $n^{{}^{\prime }}=\sqrt{1.2}n$

Q. What is mirage ? Give a reason for its formation ?

Q. Atmospheric refraction causes advance sunrise and delayed sunset. By how much time is:
(a) sunrise advanced?
(b) sunset delayed?

Q. Describe the fomation of mirage through an appropriate figure.

Q.

if sunlight is composed of seven diffferent colours, then why does the sun look orange-yellow?

Q. A beam of light propagation in medium $A$ with index of refraction $n$ $\left(A\right)$ passes across an interface into medium $B$ with index of refraction $n\left(B\right)$. The angle of incident is greater than the angle of refraction; $v\left(A\right)$ and $v\left(B\right)$ denotes the speed of light in $A$ and $B$. Then which of the following is true

1. $v\left(A\right)>v\left(B\right)$ and $n\left(A\right)>n\left(B\right)$
2. $v\left(A\right)<v\left(B\right)$ and $n\left(A\right)>n\left(B\right)$
3. $v\left(A\right)>v\left(B\right)$ and $n\left(A\right)<n\left(B\right)$
4. $v\left(A\right)<v\left(B\right)$ and $n\left(A\right)<n\left(B\right)$

Q. Which phenomenon makes us see the sun:
(a) a few minutes before actual sunrise?
(b) a few minutes before actual sunset?