With the help of activity show the blue colur of the sky and the reddish appearance of the sun at the sunrise or sunset.
Answers
Add about 1/4 cup of milk (for a 2-1/2 gallon container—increase the amount of milk for a larger container). Stir the milk into the container to mix it with water. Now, if you shine the flashlight against the side of the tank, you can see the beam of light in the water. Particles from the milk are scattering light. Examine the container from all sides. Notice if you look at the container from the side, the flashlight beam looks slightly blue, while the end of the flashlight appears slightly yellow.
Stir more milk into the water. As you increase the number of particles in the water, the light from the flashlight is more strongly scattered. The beam appears even bluer, while the path of the beam furthest from the flashlight goes from yellow to orange. If you look into the flashlight from across the tank, it looks like it is orange or red, rather than white. The beam also appears to spread out as it crosses the container. The blue end, where there are some particles scattering light, is like the sky on a clear day. The orange end is like the sky near sunrise or sunset.
How It Works
Light travels in a straight line until it encounters particles, which deflect or scatter it. In pure air or water, you can't see a beam of light and it travels along a straight path. When there are particles in the air or water, like dust, ash, ice, or water droplets, light is scattered by the edges of the particles.
Milk is a colloid, which contains tiny particles of fat and protein. Mixed with water, the particles scatter light much as dust scatters light in the atmosphere. Light is scattered differently, depending on its color or wavelength. Blue light is scattered the most, while the orange and red light is scattered the least. Looking at the daytime sky is like viewing a flashlight beam from the side -- you see the scattered blue light. Looking at sunrise or sunset is like looking directly into the beam of the flashlight -- you see the light that isn't scattered, which is orange and red.
What makes sunrise and sunset different from the daytime sky? It's the amount of atmosphere the sunlight has to cross before it reaches your eyes. If you think of the atmosphere as a coating covering the Earth, sunlight at noon passes through the thinnest part of the coating (which has the least number of particles).
Sunlight at sunrise and sunset has to take a sideways path to the same point, through a lot more "coating", which means there are a lot more particles that can scatter light.
Answer:Activity:
Place a source of light S such as an electric bulb at the focus of a converging lens L1. This lens provides a parallel beam of light.
Allow the light beam to pass through a transparent glass beaker B of capacity 500 mL.
After passing through the beaker containing about 400 mL of water allow the light beam to pass through a circular hole made in cardboard C. Obtain a sharp image of the hole on a screen MN using another convex lens L2.
Dissolve about 200 g of sodium thiosulphate (hypo) in water taken in the beaker B. Add about 1 to 2 mL of concentrated sulphuric acid with the help of an injection syringe dropwise in the beaker containing hypo solution.
What do you observe?
You will notice fine microscopic sulphur particles precipitating in about 2 to 3 seconds. As the sulphur particles begin to form, you can observe the blue light from the sides of the beaker. This is due to scattering of short wavelengths by minute colloidal sulphur particles. Observe the colour of the light patch on the screen. It is interesting to observe the change in colour of the patch-from orange red colour in the beginning to bright crimson red colour later on the screen.
image
This activity demonstrates the scattering phenomena of light that helps us to understand the bluish colour of the sky in general and the reddish appearance of the sun at the sunrise or the sunset.
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