Light

Light

What is Light ?
Ans:- Light is the form of electromagnetic energy that makes everything visible. It can detected by human eyes.

2:- What is ray of light?
Ans:- A ray of light is a narrow stream (प्रबहित होना ) of light that represents the path along which light energy travels in a medium is called ray of light.  it is represented by a straight line and an arrow marked on it. the arrow represents the direction of ray of light

3:- What is beam of light?
Ans:- A group of light rays is called beam of light.

4:-How many types of beam of light?
Ans:- There are three types of beam of light.
           1- Parallel beam of light
           2- Convergent beam of light
           3 - Divergent beam of light

5:- What is Parallel beam of light?
Ans:- When the rays of light travel parallel to each other then the collection of such rays is called parallel beam of light .

6:- What is convergent beam of light?
Ans:- When the rays of light coming from the different directions and meat at a specific point then the collection of such rays is called convergent beam of light.

                                                         Convergent beam of light

7:- What is divergent beam of light?

Ans:- When the rays of light emerge from a point source of light and travel in different direction , such beam of light is called divergent beam of light.

                                                   Divergent beam of light
8:- What is incident ray?
Ans:- A ray of light that is coming from source of light towards the reflecting surface is called incident ray of light.                 

9- What is reflecting ray?
Ans:- A ray of light bouncing away from the reflecting surface after reflection is called reflecting ray.

10- What is point of incident?
Ans:- The point on a reflecting surface where incident ray, reflecting ray and normal meet together is called point of incident.

11-What is normal?
Ans:- A line drawn perpendicular to the reflecting surface is called normal.

12- What is incidence angle?
Ans:- An angle which is formed between incident ray and normal is called incidence angle. It is represented by ' i ' 

Incidence angle = ∠i

13- What is reflected angle?
Ans:- An angle which is formed between normal and reflected ray is called reflected angle. It is represented by ' r '.

Reflected angle = ∠r 

14- What are the 2 Laws of reflection of light?  

Ans:- The two laws of reflection are

1- The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.

2-The angle of incidence is equal to the angle of reflection. , ∠i  = ∠r .

 

15:- How does the image form in plane Mirror and what is the characteristics of that Image?

                                    
                                 

Ans:- In this figure; XY is a plane mirror and O is an object. OA and OB are the incident rays; coming from the object. The incident rays are reflected from the mirror and reflected rays emerge as AC and BD. If AC and BD are extended behind the mirror, they appear to meet at point ‘I’. This is the point where image is formed. If OM is object distance and MI is image distance, then in plane mirror; OM = MI. This means in case of a plane mirror image distance is equal to object distance .

The characteristics of image formed by a plane mirror are:

• Image is always formed behind the mirror.
• It is a virtual image; which means it cannot be obtained on screen.
• Image is upright and laterally inverted.
• Image size and distance are equal to object size and distance
  

                            

16:- What is lateral inversion?

Ans:- When an object is placed in front of a plane mirror, then the right side of the object appears to become the left side of the image; and the left side of the object appears to become right side of the image. This change of the sides of an object and its mirror image is called lateral inversion.

                        

17:- What is regular reflection?

Ans:- When a beam of light falls on a smooth uniform surface (like a mirror), all the parallel incident rays are reflected perfectly parallel. This is called Regular Reflection. Regular reflection happens due to smooth surface.

                                   

 

18:- What is irregular reflection?

Ans:- When a beam of light falls on uneven or rough surface , the irregularities on a surface make the reflected rays travel in different direction . This is called irregular reflection. Irregular reflection happens due to rough surface.

                                                   

19:- What is multiple reflection?

Ans:- The phenomenon in which multiple images of an object are formed because the image formed by one mirror acts as an object for the second mirror is called multiple reflection.

 

Ex:- multiple image formed by mirror in barber's shop.                                                 

 

20:- What is the formula for finding number of images formed by multiple reflection?

 

Ans:- n = (360 / ∅ ) - 1

          Where , n = numbr of images

                       ∅ = angles between two mirrors

 

21:- What is kaleidoscope?

Ans- The kaleidoscope is a device that use reflections to produce pattern. It consists of mirror inclined to each other. The mirrors form multiple images of object in front of them. This creat a beautiful pattern, which change when the kaleidoscope is rotated or shaken.

 

22:- How can we make kaleidoscope? write steps and do project. 

Ans:- Take three strips of mirror of equal size. Tap them each other in this way that reflecting surface facing each other. Take a pouch of transparent polythene and fill it with coloured beads.now tape the transparent pouch to one end of the triangular glass tube and cover another end with stiff paper and make a hole in it. Now look through the hole and rotate the kaleidoscope. You will see beautiful patterns in it.

23:- What is prism?

Ans:- A transparent object that has reflecting surfaces and that separates white light that passes through it into different colours is called prism.

 

24:- What is angle of prism?

Ans:- The angles formed between two faces of prism is called angle of prism. It is also called reflecting angle.

 

25:- What are refrecting faces of prism?

Ans:- The two faces of prism by which light refrect are called refrecting faces of prism.

 

26:- What is dispersion of light?

Ans:- The splitting of white light into its component colours is called dispersion of light. The seven component colours are violet, indigo, blue, green, yellow, orange and red.

27:- Who was the first scientist who studied about dispersion of light?

Ans:- Sir Isaac Newton

28:- What is spectrum? How many colours an spectrum have?

Ans:- The band of colours obtained on the screen is called spectrum. It consists of seven colours in the order of violet, indigo, blue, green, yellow, orange and red.

 

29:- What is rainbow? How is it formed?

Ans:- Rainbow is a spectrum of light that is formed in the opposite direction of sun. It is formed when tiny droplets of water present in air. These water droplets act as prism and disperse the sunlight.

 

30:- What are eyes?

Ans:- Eyes are sense organs of the visual system. They detect light and convert it into electro-chemical impulses in neurons. These electro-chemical impulses is sent to the brain through the optic nerve which makes every thing visible.

 

            
31:- What is cornea?

Ans:- The outer coat of the eyes that is made of transparent material which protects the inner parts of the eyes from injury is called cornea.

32:- What is iris?

Ans:- The iris is the colored part of the eye that helps to regulate the amount of light that enters in the eye. Iris determines the colour of the eyes.                       

 

33:-  What is pupil?

Ans:- Pupil is the opening in the center of the iris. It changes size as the amount of light changes. It
determines how much light is let into the eye. In bright light , the iris expands and reduces the size of the pupil .In dull light ,the iris contracts and increases the size of the pupil so that more light can enter the eye. The pupil appears black because no light is reflected from it.

                      

 

 

 

34:-  What is eye lens?

Ans:- Eye lens is a transparent convex lens that is made of tough gelatinous material. eye lens is present behind the pupil. The ciliary muscles surround the eye lens which increase or decrease the thickness of lens. The change in thickness of lens helps to change in focal length.

                          

35:- What is retina?

Ans:- Retina is Light-sensitive tissue that lies the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses. These impulses send to the brain with the help of optic nerve. The retina is covered by a large number of nerve fibers that are very sensitive to light.

36:- What is the difference between cones and rods?

Ans:- Cones are sensitive to bright light while rods are sensitive to dim light.

37:- What is aqueous humour?

Ans:- Aqueous humour is a liquid that is filled between the space of cornea and lens.

38:- What is vitreous humour?

Ans:- Vitreous humour is a liquid that is filled between the space of lens and retina.

 

39:- What is the nature of image that is formed on the retina?

Ans:- The image formed on the retina is inverted and smaller than the object. The brain automatically interprets the image as erect and of the same size as the object.

 

40:- What is blind spot?

Ans:- The junction of the optic nerve and the retina where receptors are not present therefore an image that falls on this region will not be seen is called blind spot.

                              

41:- What is persistence of vision?

Ans:- When an object placed in front of our eyes is removed, its image does not vanish immediately from the retina. It stays there for about 1/16th of second. So, the images that are observed in quick succession do not appear as separate images, rather they look like smooth moving animation. This phenomenon is called persistence of vision.

 

42:- How can we able to see a continuous moving picture?   

Ans:-The movies actually consist of many separate pictures in a sequence. They are flashed across the eye at the rate of 24 pictures per second.Which is faster than 16 per second.So,we are able to see a continuous moving picture. 

 

43:- What is accommodation of light?

Ans:- The ability of eye to change the focal length of its lens to see the nearby as well as the distant objects clearly is called accommodation of light.

 

44:- How ciliary muscles help the eye lens to see clear image of objects at different distances?

Ans:- When the eye focuces on distant objects, the ciliary muscles relax and flatten the lens . When the eye focuses on nearby objects, the ciliary muscles contract allowing the lens to become more spherical.These adjustments change the focal length of the eye lens and help to see clear images of objects at different distances.

 

45:- What is the least distance of distinct vision?

Ans:-  A normal eye cannot clearly see objects closer than 25cm. This distance is called the least distance of distinct vision.

 

46:- What is defect of vision?

Ans:- Sometimes the thickness of the lens cannot be adjusted as required for the formation of sharp images. This is called the defect of vision.

 

47:- How many types of defects of vision in human eyes? Name them.

Ans:- There are two types of defects in human eyes.

            1- Myopia or short-sightedness

            2- Hypermetropia or long-sightedness

 

48:- What is myopia or short-sightedness?

Ans:- In myopia a person can clearly see the nearby object but he can not see the distant object clearly. This defect arises due to the eye-ball becoming long or if the distance of retina from the eye lens has increased. In this case the image of object is formed before the retina and not on the retina. This defect is usually found in young persons.

49:- How can we corrected the myopia or short-sightedness?

Ans:- myopia or short-sightedness can be corrected by using spectacles with concave lens of appropriate focal length.

 

50:- What is Hypermetropia or long-sightedness?

Ans:- In Hypermetropia a person can clearly see the distant object but he can not see the nearby object clearly. This defect arises due to the eye-ball becoming shorter or if the distance of retina from the eye lens has decreased. In this case the image of object is formed behind the retina and not on the retina. This defect is usually found in old persons.  

 

51:- How can we corrected the Hypermetropia or long-sightedness?

Ans:-Hypermetropia or long-sightedness can be corrected by using spectacles with convex lens of appropriate focal length.

 

52:- What is cataract?

Ans:- Cataract is a type of defect of human eyes. It generally happens in old age. In cataract human eye becomes clouded which leads to decrease in vision. It is the most common cause of blindness. 

 

53:- How can we corrected the cataract?

Ans:- cataract can be corrected by surgery. The opaque lens is removed and new artificial lens is inserted in its place.

 

54:- Write ten ways by which we can care of the eyes?

Ans:-  

1- Wear spectacles if you are advised to wear them.

2- Do not rub your eye if you get something in it. It can hurt your eye. Wash your eyes with water until it feels better.

3- Turn on the lights when it is getting dark.

4- Wear sunglasses and hats on bright sunny days.

5- Do not wear other peoples glasses.

6- Never look directly at the sun.

7- Wash your eyes with clean water from time to time.

8- Do not watch TV or work on a computer continuously for a long time. Take breaks to give rest to your eyes.

9- Always read at the normal distance of vision 25cm.Do not keep the book too close or too far from the eyes.

10- Eat healthy food reach in vitamin A.Raw carrots,cod liver oil,eggs, papaya, milk, green vegetables like spinach,etc. are rich in vitamin A.Lack of vitamin A can cause a disease called night blindness.