Refraction of light
Why is the star appear twinkling in the sky?
The visible position of the star retains changing a bit because of the atmospheric air's motion, changing air density, and temperature. Because of these, the refractive index of air keeps changing continuously, also changes the position and brightness of the star. It keeps changing continuously and the star appears to be twinkling.
Star appears to be higher in the sky as compared to its actual position. Give reason.
- Self-luminous and to be point sources:
Stars are self-luminous and can be seen at night, in the absence of sunlight. They appear to be point sources because they are being at a very large distance from us.
- The density of air increases:
The density of air increases with lowering height above the surface of the earth, the refraction index also increases.
- Bend towards Normal:
Starlight coming towards us travels from rarer medium to denser medium and constantly bends towards the normal. Therefore, stars appear to us higher than the actual position.
Why do we not see the twinkling of the planets?
- Closer distance:
Planets are much closer to us as compared to stars.
- Collection of point sources:
Planets do not appear as point sources but appear as a collection of point sources.
- Total average brightness remains unchanged:
Those atmospheric refractive index changes the position and brightness of individual point source, the average position, and total average brightness remain unchanged and planets do not twinkle.
Why does the refractive index of a medium be different for different colors?
The velocity of light rays of all frequencies is the same in a vacuum. But the velocity of light in a medium depends on the frequency of light and the different colors travel with different velocities.
How do we get a spectrum of seven colors to obtain from the glass prism?
- When white light is incident on the prism, divergent colors bend through different angles. Among the seven colors, red bands the least while violet bends the most.
- The seven colors emerge along different paths and get separated, and we get a spectrum of seven colors.
Small droplets of water act as a small prism. Give reason.
How is a rainbow produced by dispersion refraction and total internal reflection
Define total internal reflection.
- Angles of incidence are larger than the critical angle. The angle of reflection is larger than 90 degrees. Such rays return to the denser medium.
- Thus, all the light gets reflected back into the dense medium this is called total internal reflection.
Define dispersion of light.
The process of the split of light into its constituent colors while passing through a medium is called dispersion of light.
Define Mirage.
Light rays coming from a distance of the object of year to the coming from the image of the object inside the ground. This is called a mirage.
