What is meant by spectrum of light? Which colour of spectrum deviates the most and which the least?

The band of colours obtained on a screen on passing white light through a prism is called a spectrum. The various colours seen are Violet, Indigo, Blue, Green, Yellow, Orange, and Red. The band of the coloured components of a light beam is called its spectrum. All the colours of white light have different wavelengths and their deviation is also different. Also, the violet colour has the least wavelength. Therefore, when it travels from one medium to another, then it has the maximum value of the angle of incidence and the violet colour will deviate the most. But the red colour has a maximum wavelength, so it will deviate the least.

Explain the phenomenon of Rainbow formation.

Formation of Rainbow : (a) The beautiful phenomenon of the rainbow is a combination of three different phenomena - dispersion, refraction, and reflection of light. (b) The rainbow appears in the sky after a rain shower. (c) When light rays from the sun enter the water droplets that act like small prisms, they refract and disperse the incident sunlight. (d) This light is then reflected internally, inside the droplet, and is finally refracted again. (e) Due to the collective effect of all these phenomena, the seven coloured rainbow VIBGYOR - violet, indigo, blue, green, yellow, orange, red can be seen.

What is the far point and near point of the human eye with normal vision?

The farthest point up to which the eye can see objects clearly is called the far point of the eye. It is infinity for a normal eye. The minimum distance at which objects can be seen distinctly is called the near point of the eye. It is 25 c m for a normal human eye. In other words, the distance of the near point of a normal eye is called the least distance of distinct vision.

Why does the sky appear dark instead of blue to an astronaut?

The sky appears dark instead of blue to an astronaut because there is no atmosphere in outer space that can scatter the sunlight. As the sunlight is not scattered, no scattered light reaches the eyes of the astronauts and the sky appears black to them. Gases and particles in Earth's atmosphere scatter sunlight in all directions. Blue light is scattered more than other colours because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

What is meant by Myopia? Write the causes and correction of this defect.

A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. A person with this defect has the far point nearer than infinity. Such a person may see clearly up to a distance of a few metres. In a myopic eye, the image of a distant object is formed in front of the retina. This defect may arise due to (i) excessive curvature of the eye lens, (ii) elongation of the eyeball. Correction-The cure for the nearsighted eye is to equip it with a diverging lens. Since the light is focused in front of the retina, a diverging lens will serve to diverge light before it reaches the eye. This light will then be converged by the cornea and lens to produce an image on the retina.

What do you mean by spectrum of light? Which colour of spectrum deviates the most and which the least?

The band of colours obtained on a screen on passing white light through a prism is called a spectrum. The various colours seen are Violet, Indigo, Blue, Green, Yellow, Orange, and Red. The band of the coloured components of a light beam is called its spectrum. All the colours of white light have different wavelengths and their deviation is also different. Also, the violet colour has the least wavelength. Therefore, when it travels from one medium to another, then it has the maximum value of the angle of incidence and the violet colour will deviate the most. But the red colour has a maximum wavelength, so it will deviate the least.