Human Eye - MCQ Test (22-11-2017) - Class 10 MCQ

The far point  is  infinity  for  normal  eye.  It  is  the farthest  point  upto which  the  eye  can see object clearly.

The defect by which the person is not able to differentiate horizontal and vertical position, is called astigmatism. It is caused by an error in the shape of the cornea.  It can be corrected by using cylindrical lenses.

According to Snell’s law, ratio of the sine of the angle of incidence to the sine of the angle of refraction is always constant for a given pair of media. Therefore, if the angle of incidence increases, the angle of refraction also increases proportionally to the increase of incidence.

Both of these phenomena are due  to atmospheric  refraction. The temperature and density of different layer of atmosphere keeps varying. When the light enters the earth’s atmosphere it undergoes refraction continuously, due to changing refractive index  i.e. light travels from rarer  to denser medium and hence It bends  towards  the normal successively.

When ray of light enters from a rarer medium (air) into a denser medium (water), it bends towards normal at the point of incidence.

The bending of light as it passes from one medium to another is called refraction. The angle and wavelength at which the light enters a substance and the density of that substance determine how much the light is refracted. The bending occurs because light travels more slowly in a denser medium.

Hence, by a glass prism as well as a rectangular glass slab

The lateral displacement of an incident ray passing out of a rectangular glass slab is directly proportional to the thickness of glass slab, angle of incidence, and refractive index however it is inversely proportional to the wavelength of incident light.

Hypermetropia (Long sightedness) is caused due to
1. Decrease in curvature of eye  lens  (thin eye lens, increase  focal  length)
2. Eye ball has become  too  small.

Retina works like a screen or camera film. Retina is full of light and colour sensitive cells. These cells, upon receiving image send electrical signals to the brain, which processes these information to make a mental image of what we see.

Dispersion is the phenomena of splitting of white light into its constituent seven colours (VIBGYOR) on passing through a glass prism.

Advance Sunrise and delayed  sunset: This  is  due  to atmospheric  refraction. Because of this sun is visible about 2 minutes earlier than actual sunrise and about 2 minutes after  the actual  sun  set.

The photoreceptor cells in the retina are of two types, viz. rod cells and cone cells. The rod cells are sensitive to dim light whereas the cone cells are sensitive to bright light (daytime) and colour.

If you mix red, green, and blue light, you get white light. Red, green, and blue (RGB) are referred to as the primary colors of light. This is additive color system. As more colors are added, the result becomes lighter, heading towards white. RGB is used to generate color on a computer screen, a TV, and any colored electronic display device.

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.

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

It is due to: 

1. Elongation of  the eye ball
2. Excessive curvature of eye  lens  (thick eye lens→ decrease in focal  length→ increase in power of lens)

The rainbow is a natural spectrum of sunlight appearing in the sky after a rain shower. It  is  formed due  to  the dispersion of  sunlight by  the  tiny water droplet, present  in atmosphere. Water droplet act  like prism. It  refract  and  disperse  the  incident  sunlight,  then  reflect  it  internally  (total internal reflection) and  finally  refract  it again, when  it emerges out of  the water droplet. Red colour appear on  top & violet at  the bottom of  rainbow.

The refractive index is a measurement of optical density. A medium with a low optical density, would have also a low refractive index.

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.

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.

Eye donation actually means cornea donation. Conditions like myopia and hypermetropia are refractive errors. These are corrected using spectacles and cornea is otherwise healthy, therefore a person who wears spectacles can donate eyes without any problem.

Hypermetropia is also known as far-sightedness. In hypermetropia, a person cannot see nearby object clearly, but can see distant object clearly.

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.Correction- Using of Bifocal  lens with appropriate power. Bifocal  lenses consist of both concave and convex  lens, upper position consist of concave  lens and  lower portion consist of convex  lens.

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

Red colour  scattered  the  least when  strikes  by the  small particle of  fog and smoke because it has the maximum wavelength (visible spectrum). Hence at  large distance also, we can  see  the  red colour clearly.

When image formed at retina, light sensitive cells get activated and generate electrical signal. These signals are sent to brain via optic nerve.

Electromagnetic waves (or electromagnetic radiation) are waves made of oscillating magnetic and electric fields, and include radio waves, microwaves, infrared, visible light, ultraviolet, x-rays and gamma rays. Thus, light is just one part of the electromagnetic spectrum, the part that our eyes can see.

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.

Applications of optical fiber include:

1. Communication: Telephone transmissoin method usese fiber-optic cables. Optical fibres transmit energy in the form of light pulses.
2. Medical uses: Optical fibres are well suited for medical use. They can be made in extremely thin, flexible stands for insertion into the blood vessels, lungs, and other hollow parts of the body. Optical fibers are used in a number of instruments that enable doctors to view internal body parts without having to perform surgery.
3. Simple uses: The simplest application of optical fibers is the trnsmission of light to locations otherwise hard to reach.

The pupil of an eye provide a variable aperture, whose  size  is controlled by iris
a) When the light is bright: Iris contracts the pupil, so that less light enters the eye.
b) When  the  light  is dim:  Iris expand  the pupil,  so  that more  light enters  the eye. Pupil open completely, when  iris  is  relaxed.

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.

The retinal cones of bees are sensitive to ultraviolet light. Hence bees respond to ultraviolet light.