1. Why do stars twinkle and hence why do planets do not twinkle? 2. Give reason for the following: (a) Blue colour of the sky (b) Red colour of danger signals. 3. Give reason for the following (a) White colour of clouds (b) Sun appears red at the time of sun set and sun rise. 4. Explain Tyndal Effect. 5. What is rainbow? Give the conditions for observing it. State the principle involved in the formation of rainbow.
Answers
The stars appear to be "twinkling" because the earth atmosphere is more denser than that of the outer space and hence the atmosphere of the earth refracts the light of the stars. The stars are so far from earth as a definite position cannot be seen. So it appears to be glittering. A similar phenomenon is sky looking blue in colour, which appears to be blue because of the colour wavelength captured by human eye. But as stars are not as vast as space and also they are far beyond (nearest star except sun which doesn't twinkle, is proxima centauri which is 10x10^13 miles.. 100,000,000,000,000 miles).
2 (a)To answer this questio you should know about atmosphere and light.
The atmosphere is the mixture of gas molecules and other materials surrounding the earth. It is made mostly of the gases nitrogen (78%), and oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice crystals) are the next most common things. There are also small amounts of other gases, plus many small solid particles, like dust, soot and ashes, pollen, and salt from the oceans.
Light is a kind of energy that radiates, or travels, in waves. Many different kinds of energy travel in waves. For example, sound is a wave of vibrating air. Light is a wave of vibrating electric and magnetic fields.
Electromagnetic Waveslight waveIt is one small part of a larger range of vibrating electromagnetic fields. This range is called the electromagnetic spectrum.
Electromagnetic waves travel through space at 299,792 km/sec (186,282 miles/sec). This is called the speed of light.
The energy of the radiation depends on its wavelength and frequency. Wavelength is the distance between the tops (crests) of the waves. Frequency is the number of waves that pass by each second. The longer the wavelength of the light, the lower the frequency, and the less energy it contains.The blue color of the sky is due to Rayleigh scattering.
As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.
However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.
As you look closer to the horizon, the sky appears much paler in color. To reach you, the scattered blue light must pass through more air. Some of it gets scattered away again in other directions. Less blue light reaches your eyes. The color of the sky near the horizon appears paler or white.
(b)the color red is used for danger signals is that red light is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a color. Therefore blue which has the least wavelength of all the visible radiations is scattered the most and red which has the highest wavelength of all the colors we can see is scattered the least. So red light is able to travel the longest distance through fog, rain, and the alike.Also, red is a color we inherently perceive as one that is associated with danger. I guess it has been genetically programmed as hot objects are red in color and also red is the color of blood. These reasons make danger signals the most effective when they are painted in red.