Human Eye and Colourful World Test - 10

The sky appears blue due to scattering of the blue colour by the earth's atmosphere. In moon there is no atmosphere hence nothing to scatter light. Thus, the sky appears dark as seen from the moon surface.

When a white light is passed through a prism it gets split into combination of seven colours which is known as the spectrum. The colors of the spectrum of white light are those seen in a rainbow. They are usually named in order as: red, orange, yellow, green, blue, indigo and violet.

Bifocal  lenses consist of both concave and convex  lens, upper position consist of concave  lens and  lower portion consist of convex  lens.

In myopia or nearsightedness, a person can see nearby object clearly, but cannot see distant object distinctly. Image formed in front of the retina.

In hypermetropia also known as farsightedness, a person cannot see nearby object clearly, but can see distant object distinctly. Image formed at a point behind the retina.

As we become old,  the power of accommodation of the eye usually decreases, the near point gradually recedes away. This defect is called presbyopia. Person may suffer from both myopia and hypermetropia.

The ability of the eye to focus both near and distant objects, by adjusting the focal length of the eye lens, is called the accommodation of the eye.

It is the fixed distance between the cornea and the retina and is approximately 2.5 cm in length in the average adult.

The image on the retina is formed by two lenses – the cornea, which is a converging lens whose focal length is fixed, and the eye-lens, which is a convex lens whose focal length is not fixed and can be varied by changing its shape.

In optics, an aperture is a hole or an opening through which light travels. The pupil of the eye is its aperture in optics nomenclature; the iris is the diaphragm that serves as the aperture stop.

Twinkling of stars  is due  to atmospheric  refraction. Distant star acts like a point source of light. When the starlight enters the earth’s atmosphere it undergoes refraction continuously, due to changing refractive index  i.e.  from Rarer  to denser medium. It bends  towards  the normal successively, hence  the amount of  light enters our eyes  fluctuates  sometime bright and  sometime  faint.