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

[question] Question. Why does the sky appear dark instead of blue to an astronaut ? [/question] [solution] solution: The sky appears dark instead of blue to an astronaut because there is no atmosphere in the 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. [/solution]...

Why does the Sun appear reddish early in the morning ?

[question] Question. Why does the Sun appear reddish early in the morning ? [/question] [solution] solution: In the morning, the sun is near the horizon. Light reaching the eye of an observer travels a larger distance in the atmosphere. Thus, most of the blue light and shorter wavelength rays are scattered away by the air particles. Hence, the light that reaches the eye of an observer is of longer wavelengths (of red end). Thus, the sun appears reddish at sunrise or sunset. [/solution]...

Explain why the planets do not twinkle.

[question] Question. Explain why the planets do not twinkle. [/question] [solution] solution: The apparent size of stars is very small as compared to apparent size of planets. Thus, the star may be considered as a ‘point sized’ source of light and the planet as an ‘extended source’ of light. So, the planet can be considered as a collection of large number of ‘point sized’ sources of light, such that the dimming effect of some ‘point sources’ is nullified by the brighter effect of the other ‘poin...

Why do stars twinkle ?

[question] Question. Why do stars twinkle ? [/question] [solution] solution: Twinkling of stars can be seen on a clear night. This is due to atmospheric refraction of light coming from the stars (star light). As the star light enters into the earth’s atmosphere, atmospheric refraction takes place due to gradually changing refractive index of the air. Since the physical conditions of the refracting medium (earth’s atmospheric) are not stationary, star light flux (luminous flux) entering the eye o...

What happens to the image distance in the eye

[question] Question. What happens to the image distance in the eye when we increase the distance of an object from the eye ? [/question] [solution] solution: The size of eye cannot be increased or decreased. Therefore, the image distance remains constant. When we increase the distance of an object from the eye, the image distance in the eye does not change. The increase in the object distance is compensated by the change (increase) in the focal length of the eye lens such that the image is forme...

Why is a normal eye not able to see clearly

[question] Question. Why is a normal eye not able to see clearly the objects placed closer than 25 cm ? [/question] [solution] solution: A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit. If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes. [/solution]...

Make a diagram to show how hypermetropia is corrected.

[question] Question. Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect ? Assume that the near point of the normal eye is 25 cm. [/question] [solution] solution: Here, y = 1 m $\frac{1}{f}=\frac{1}{0.25}-\frac{1}{y}=\frac{1}{0.25}-\frac{1}{1}$ $=\frac{100}{25}-1=4-1=+3$ or $\mathrm{f}=+(1 / 3)=+0.3333 \mathrm{~m}=+33.33 \mathrm{~cm}$ Power, $P=\frac{1}{f}=+3$ dioptres. [/solution]...

The far point of a myopic person is 80 cm in front of the eye.

[question] Question. The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem ? [/question] [solution] solution: For myopia, focal length is given by, $\mathrm{f}=-\mathrm{x}=-80 \mathrm{~cm}=-\mathbf{0 . 8} \mathrm{m}$ Power, $\mathrm{P}=\frac{1}{\mathrm{f}}=\frac{1}{-0.8}$ $=-1.25$ dioptres. The lens is a concave lens. [/solution]...

The change in focal length of an eye lens is caused by the action of the

[question] Question. The change in focal length of an eye lens is caused by the action of the (a) pupil (b) retina (c) ciliary muscles (d) iris [/question] [solution] solution: Option (c) is correct. By relaxation or contraction of ciliary muscles, the curvature of the eye lens changes which eventually changes the focal length of eye lens. [/solution]...

The least distance of distinct vision for a young adult with normal vision is about

[question] Question. The least distance of distinct vision for a young adult with normal vision is about (a) 25 m (b) 2.5 cm (c) 25 cm (d) 2.5 m [/question] [solution] solution: Option (c) is correct. The least distance of distinct vision is the minimum distance of an object to see clear image. It is 25 cm for a young adult with a normal vision. [/solution]...

The human eye can focus objects at different distances

[question] Question. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to (a) presbyopia. (b) accommodation. (c) near-sightedness. (d) far-sightedness. [/question] [solution] solution: Option (b) is correct. Human eye can change the focal length of the eye lens to see the objects situated at various distances from the eye. This ability of eye is called accommodation. [/solution]...

What is the far point and near point of the human

[question] Question. What is the far point and near point of the human eye with normal vision ? [/question] [solution] solution: The far point of a human eye with normal vision is at infinity while the near point is at 25 cm from the eye. [/solution]...

A person with a myopic eye cannot see objects beyond 1.2 m distinctly.

[question] Question. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision ? [/question] [solution] solution: To correct this defect of vision, he must use a concave lens. [/solution]...

What is meant by power of accommodation of the eye ?

[question] Question. What is meant by power of accommodation of the eye ? [/question] [solution] solution: The ability of the eye lens to adjust its focal length is called power of accommodation. [/solution]...