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Page No 216:

Question 1:

What is reflection?

Answer:

When light rays fall on any polished surface, the light rays return back after striking the surface. This bouncing back of light rays from any polished surface is called the phenomenon of reflection. 

Page No 216:

Question 2:

What is the relationship between the angle of incidence and the angle of reflection?

Answer:

When a light ray falls on any reflecting surface, the angle of incidence (which is the angle between the normal and the incident light ray) is always equal to the angle of reflection (the angle between the normal and the reflected light ray). This is the second law of reflection of light.

Page No 216:

Question 3:

What is lateral inversion?

Answer:

Lateral Inversion: The reversal of  appearance of an object, pictures or letters from left to right when the image is formed by a plane flat mirror is called left- right reversal or lateral inversion.

Page No 216:

Question 4:

What is the blind spot in an eye?

Answer:

A small portion in the retina which is insensitive to light is called blind spot. Blind spot is an area on the retina where the nerve endings enter the optic nerves. Since, this area has no visual receptors such as rods and cones, the images falling on this area cannot be detected.

Page No 216:

Question 1:

Write one word for the following.

1. The left-right inversion ....................
2. Reflection from diffused surface ....................
3. The coloured part of the eye ....................

Answer:

1. Lateral Inversion
2. Diffused reflection
3. Iris

Page No 216:

Question 2:

Define/Explain the following.
1. Spectrum
2. Dispersion
3. Persistence of vision
4. Cataract

Answer:

  1. Spectrum: The whole range of colours, visible during dispersion, with which white light is formed is called spectrum.
  2. Dispersion: The phenomenon of splitting of white light into its constituent colours is called dispersion.
  3. Persistence of vision: The phenomenon of the eye where an afterimage is retained, but only for a short period of time, after the removal of the object.
  4. Cataract:  A condition in which the lens of the eye becomes opaque or cloudy resulting in blurred or dimmed vision.

Page No 216:

Question 1:

Which of the following is the correct statement of the first law of reflection?
(a) The incident ray and the reflected ray lie in the same plane.
(b) The incident ray, the reflected ray, and the normal at the point of incidence lie in the same plane.
(c) The incident ray and the reflected ray are in the plane of the mirror.
(d) The incident ray, the refracted ray, and the normal lie in the same plane.

Answer:

(b) The incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.

Page No 216:

Question 2:

When an image is formed by a plane mirror, the
(a) image size is smaller than the object size.
(b) image size is greater than the object size.
(c) image size is the same as the object size.
(d) image size depends on the distance of the object from the mirror.

Answer:

(c) The image size is same as the object size
When an image is formed by a plane mirror, the image and the object size are the same

Page No 216:

Question 3:

Which of these is not a luminous object?
(a) Star
(b) Sun
(c) Tree
(d) Light bulb

Answer:

(c) Tree
Tree is not a luminous object because it does not emit light on its own.

Page No 216:

Question 4:

If we keep an object in front of two plane mirrors at an angle of 90° to each other, we will get
(a) one image
(b) two images
(c) three images
(d) four images

Answer:

(c) three images

We will get three images of the object when the two plane mirrors are kept at an angle of 90° to each other.

Page No 216:

Question 5:

The process of splitting up of white light into its constituent colours is called
(a) spectrum
(b) newton's disc
(c) dispersion
(d) rainbow

Answer:

(c) dispersion
The splitting of white light into its constituent colours is called dispersion.

Page No 216:

Question 1:

Match the following.

Column A Column B
Bouncing off light Normal
Upright Left-right reversal
Lateral inversion Reflection
Perpendicular to the mirror surface Erect image

Answer:

Sl.No Column A Column B
1. Bouncing of light Reflection
2. Upright Erect Image
3. Lateral Inversion Left -right reversal
4. Perpendicular to the mirror surface Normal



Page No 217:

Question 1:

State the laws of reflection.

Answer:


The bouncing back of light from any polished surface is called reflection. The two laws of reflection are:

  1. The incident ray, the reflected ray and the normal at the point of incidence lie on the same plane.
  2. The angle of incidence is equal to the angle of reflection.

Page No 217:

Question 2:

Write down the characteristics of an image formed by a plane mirror.

Answer:

The following are the characteristic of the image formed by a plane mirror:

  1. Size of the image formed by a plane flat mirror is always the same as that of the object.
  2. A plane flat mirror always produces an upright or erect image of the object
  3. The distance of the image from the plane mirror when compared to the distance of the object from the mirror is always equal.
  4. A plane mirror reverses the image of the object or letters from left to right. This effect is called left-right reversal or lateral inversion.

Page No 217:

Question 3:

Describe the structure and parts of the human eye.

Answer:

Structure: The human eye is a very small, sensitive organ about 2.5 cm in length which enables vision. The eyelids protect the eye from injuries and therefore, they are known as shutters of the eye.

Parts of the eye: The internal parts of the eye are:
Pupil: This is the inner aperture in the centre of the eye through which light enters.
Iris: Iris is the coloured part of the eye which regulates the amount of light entering the pupil by decreasing and increasing the size of the pupil.
Sclera: Sclera is the white part of the eye which contains clear watery fluid.
Cornea: A thin transparent layer in front of the eye is cornea.
Retina: Retina is the lining behind the eyeball which has visual receptors such as rods and cones.
Ciliary muscles: The muscles in the eye which alters the curvature of the eye lens are ciliary muscles
Lens: A transparent tissue between the pupil and retina which helps in focussing light.
Optic Nerve: The nerve that connects the eye to the brain transmitting impulses to brain and back to the eye is called optic nerve
Blind spot: A portion in the retina which is insensitive to light where the nerve ending enter the optic nerve. This area does not have any rods and cones.

figure

Page No 217:

Question 4:

What is myopia and hypermetropia? How can they be corrected?

Answer:

To see clearly, rays of light from an object must be focussed to a point on the retina by the eye lens.

Myopia: If the eyeball is not spherical but slightly elongated, then the rays of light from a distant object converge to a point ahead of the retina. As a result, distant objects appear blurred and unclear. The condition where distant objects are not clearly seen is known as myopia or near sightedness. Myopia can be corrected by using spectacles or contact lens with concave lens. The concave lens cause the light coming from a distant object to diverge slightly before entering the eye so that they are brought to focus on the retina.

Hypermetropia: If the eyeball is slightly compressed, then the rays of light from a near by object do not converge by the time they reach the retina. As a result, near by objects appear blurred and unclear. The condition where near by objects are not clearly seen is known as hypermetropia or far sightedness. Hypermetropia can be corrected using spectacles or contact lens with convex lens so that the light can be brought to focus on the retina.

Page No 217:

Question 5:

Write a note on the alternate technology for the blind people.

Answer:

The rapid advancement of technology over the years has led to an improvement in the assistance available to the visually impaired, which helps improve their quality of life:

  1. Several devices such as portable braille typewriter, talking calculator, dictaphone, audio measuring devices are very helpful to the blind.
  2. Personalized blind friendly computers with customized software are available today which provides an easy access to information on internet to the blind.
  3. Special scanners, printers and keyboards are available for the blind enabling them easy access of information.

Page No 217:

Question 6:

Explain how nutrition affects eye health.

Answer:

Eye health is mainly dependent on the food we eat and the proper absorption of nutrients. Eating foods rich in vitamin A, C and E supplies the nutrients and antioxidants required for maintaining the health of the eye.  Foods such as carrots, broccoli, egg and tomatoes which are rich in vitamin A keep the eye healthy and prevent the condition of night blindness (xerophthalmia). Most of the coloured fruits and vegetables contain antioxidants called carotenoids which help in maintaining good vision and delaying age related blindness.



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