Light Blog 10

CLASS 8 CHAPTER 16

Light
Day 10

Dear Learners,

In the previous blog, we have learned about Eye- Structure and Function. Let me help you to recall few important points

1. The eye is a most important sense organ.

2. Eye resembles a camera in many ways.

3. The main parts of the eye are (i) cornea  (ii) Iris & pupil   (iii) Eye lens       (iv) Retina  (v) Blind spot.

I hope you all have well understood the previous blogs. If you have any doubts feel free to write in comment box.

Today, we will be learning about one of most important phenomenon that happen in our brain due to eye. i.e. Persistence of Vision. We will also be learning about defects of vision.

Happy Learning!😊

At the end of it, you will be able to:

1. define persistence of vision.

2. tell the importance of persistence of vision.

3. explain the major defects of vision.

4. explain the corrective measure for defect of vision.

So, lets start the topic....................

Persistence of Vision

Let us understand this topic by seeing the link the below:

https://www.youtube.com/watch?v=JsU9lcM2ACs 

I hope you have noticed that we were able to retain the images of flip book given on different pages. 

Do you all have any idea, how was that possible?????

This is due to the phenomenon "Persistence of Vision". 

The image formed on the retina persists for 1/16th of a second after we have stopped looking at the object. The ability of the eye to retain the image of the object for 1/16th of a second after we have stopped looking at the object is called persistence of vision.

https://www.youtube.com/watch?v=L0VIxZmzZbs

Real Life Application: 

1. Earlier, making cartoon film was very expensive. The cartoonist need to draw every cartoon for every different action. These pictures were then shot giving the look of one complete film.

2. Even today, the phenomenon of the persistence of vision is employed in the motion pictures projection. 

3. In chapter sound, you will be learning about persistence of sound. So, we can say that a movie is good combination of persistence of sound and light both. 

Activity: https://www.youtube.com/watch?v=KbjcfSXtO3c

Now, let us move next topic.....

You must have came across people wearing spectacles who have difficulty in seeing things. But have ever thought about the reason for it?? 

So, let us learn more about it.

Defects of Vision

The abnormalities in the normal vision of the eye are called defects of vision or defects of eyes.

The most commonly observed defects of visions are:

(i) Myopia or short-sightedness

(ii) Hypermetropia or long-sightedness.

Mypoia

Myopia is defect due to which a person suffering can see the nearby objects clearly but cannot see the far off objects clearly.

Correction: By using concave lenses of suitable focal length.

Hypermetropia 

Hypermetropia is defect due to which a person suffering can see the distant object clearly but cannot see the nearby object.

Correction: By using convex lenes of suitable focal length.

https://www.youtube.com/watch?v=ldfJGTC0ZQ0

Home Assignment
1. Do Quick Assignment page no 263 Section A, B, C, in your reader.
2. Read page no 258-260.