Human Eye and Colourful World Test - 36

Nearsightedness occurs when there is a mismatch between the focusing power of the eye and the strength of the eye. Light rays from distant objects are focused in front of the retina, rather than directly on it. As a result, what we see is blurry. 

Correct answer is (b)

Power of Accommodation is the ability of the eye lens to adjust its focal length. The ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina.

When the muscles are relaxed, the lens becomes thin. Its focal length increases. This enables us to see distant objects clearly. 

To look at objects closer to the eye, the ciliary muscles contract. The eye lens then becomes thicker. The focal length of the eye lens decreases. This enables us to see nearby objects clearly.

Correct answer is (c).

Long-sightedness, affects a person's ability to see objects close to them, these vision problems are also referred to as refractive errors. A person having long-sighted eye, usually is able to see distant objects clearly, but nearby objects will be out of focus, and as the man cannot see the objects distinctly at a distance less than 1 meter so he is suffering from Long-sightedness.

Myopia is also known as near-sightedness. 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 meters.

The distance of far point $$X=2m$$ 

Take two glass prisms P1 and P2 and place the second prism P2 upside down with respect to the first prism P1. Now, allow a beam of white light to fall on first prism P1. The first prism splits the white light into seven colors. When these colors fall on the inverted prism, it recombines all the colors into white light which is observed ultimately as a patch of white light on the screen.

Correct answer (a)

The eyeball is approximately spherical in shape with a diameter of about 2.3 cm. 

Hypermetropia is a defect in which a person is unable to see close objects clearly. The near point, for the person, is farther away from the near point of normal people (25 cm).

Correct answer (a)

The power of accommodation of the eye usually decreases with ageing. For most people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses. This defect is called Presbyopia. It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the eye lens. 

Sometimes, a person may suffer from both myopia and hypermetropia. Such people often require bi-focal lenses. The upper portion consists of a concave lens. It facilitates distant vision. The lower part is a convex lens. It facilitates near vision.

Answer is D.

The rainbow is caused by light from the sun (or moon) interacting with raindrops falling from the air. These raindrops are mostly round. A ray of light entering such a droplet is bent (refracted) and decomposed into all possible colors (wavelengths) which the white light consists of. The ray then reflects internally in the droplet, and emerges roughly into the direction it came from when it entered the drop. Since the rays of the different colors all exit at slightly different directions, we see a color band in the sky.
The colors are produced by a phenomenon called dispersion. Dispersion causes white light, which consists of all possible colors to break up into all components, when the light travels from one medium (e.g. air) to another (e.g. water). The different colors of light have all slightly different directions, so if we look in a certain direction in the sky we can see the spectrum.