Life Processes

The maintenance function of living organisms must go on even when they are not doing anything particular. Even we are just sitting in home, even if we are just asleep, this maintenance job has to go on. The processes which together perform this maintenance job are life processes.
Since these maintenance processes are needed to prevent damage and break-down, energy is needed for them. This energy comes from outside of the body of the individual organism, which we call food, to the inside, a process we commonly call nutrition. If the body size of the organisms is to grow, additional raw material will also be needed from outside. Since life on earth depends on carbon-based molecules, most of these foods sources are also carbon-based. Depending on the complexity of these carbon sources, different organisms can then use different kinds of nutritional processes.

Working of our eye (physics)

About eye

The human eye is one of the most valuable and sensitive sensitive organs.It enables us to see the world and the colors around us. On closing the eyes , we can identify objects to some extent by their smell, taste, sound they make or by touch. it is however, impossible to identify colors while closing the eyes. Thus, of all the sense organs, the human eye is the most significant one as it enables us to see the beautiful, colorful world around us.

The human eye is like a camera. Its lens system forms an image on light-sensitive through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball as shown in figure.

We find structure called iris behind cornea. Iris is a dark muscular diaphragm that controls the size of pupil.The pupil regulates and controls the amount of light entering the eye.

Atmospheric Refraction

You might have observed the apparent random wavering or flickering of objects seen through a turbulent stream of hot air rising above fire or a radiator. The air just above the fire becomes hotter than the air further up. The hotter air is lighter (less denser) than the cooler air above it, and has a refractive index slightly less than that of the cooler air. Since the physical conditions of the refracting medium are not stationary, the apparent position of the object , as seen through the hot air, fluctuates. This wavering is thus an effect of atmospheric refraction on a small scale in our local environment. The twinkling of stars is a similar phenomenon on much larger scale. Let us see how i can explain it.

Twinkling of stars:

The twinkling of star is due to atmospheric refraction of starlight. The starlight, on entering the earth's atmosphere, undergoes refraction continuously before it reaches the earth. The atmospheric refraction occurs in a medium of gradually changing refractive index. Since the atmosphere bends starlight towards the normal , the apparent position of the appears slightly different from its actual position . The star appears slightly higher than its actual position when viewed near horizon (see in figure). Further, this apparent position of stars is not stationary, but keeps changing slightly, since the physical conditions of the earth's atmosphere are not stationary , as was the case in atmospheric refraction . Since the stars are very distant, they approximate point-sized sources of light. As the path of rays of light coming from the star goes on varying slightly , the apparent position of the star fluctuates and the amount of starlight entering the eye flickers - the star sometimes appears brighter, and at some other time, fainter, which is the twinkling effect.

Why is the color of the clear sky blue ?

The molecule of air and other fine particles in atmosphere have size smaller than the wavelength of visible light. These are more effective in scattering light of shorter wavelengths at the blue and than light of longer wavelengths at the red end. The red light has a wavelength about 1.8 times greater than blue light. thus, when sunlight passes through the atmosphere, the fine particles in air scatter the blue color more strongly than red. The scattered blue light enters our eyes. If the earth had no atmosphere, there would not have been any scattering. Then, the sky would have looked dark. The sky appears dark to passengers flying at very high altitudes, as scattering is not prominent at such heights.


Tyndall Effect

The earth's atmosphere is a heterogeneous mixture of minute particles. These particles include smoke, tiny water droplets , suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of beam becomes visible. The light reaches us, after being reflected diffusely by these particles. The phenomenon of scattering of light by colloidal particles gives rise to  Tyndall effect. This phenomenon is seen when a fine beam of sunlight enters a smoke-filled room through a small hole. Thus, scattering of light makes the particles visible. Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest. Here tiny water droplets in the mist scatter light.