Kiến thức về mắt: Cấu tạo của mắt, mắt cận và mắt lão (Vật Lý 9)

Eyes are the part that ensures our observation anytime, anywhere. The structure of the eye is very complex and sophisticated. Therefore, the following article will help you learn more about the structure and functioning of the eyes.

Describe the structure of the eye

Learn about the structure of the eye, compare the eye with a camera.

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Structure of the eye

The eye is made up of two extremely important main parts. These are the vitreous body and the reticular membrane (also known as the retina).

• Vitreous body: considered a biological focusing lens, the properties of the vitreous body are soft and transparent, easily flattened or bulged. The reason for this change is that the sphincter supporting the lens expands or contracts, causing its focal length to change.

• Reticular membrane: located at the bottom of the eye, here we will see clearly the image of any object.

Compare eyes and cameras

Alike:

Different:

Eye regulation

When we see an object clearly, the image of that object will appear clearly on the reticle. At the same time, the sphincter supporting the lens has to stretch appropriately and cause the lens to flatten or bulge, which also changes the focal length of the lens. This process of change is called eye accommodation.

Regulation occurs completely naturally.

When the eye observes objects at a close distance, the focal length of the eye becomes smaller. On the contrary, when the eyes observe objects at a distance, the negativity of the eyes will be greater.

Near and far points of the eye

The following are concepts and characteristics related to the near and far points of the eye.

What is the near point of the eye?

The point closest to the eye that when any object is there, our eyes can still clearly observe the object (when the eye adjusts to its maximum) is called the extreme near point. As you get older, the near point will recede further from the eye.

Symbol for the near point of the eye: Cc.

The near point is determined by the distance from the eye to the near point.

What is the far point of the eye?

The point farthest from the eye where, when any object is there, our eyes can still clearly observe the object without adjusting is called the far point.

Symbol for the far point of the eye: Cv

The far point is determined by the distance from the eye to the far point.

Attention:

• The distance from the near point to the far point is called the eye's visual limit.

• The image of an object caught on the mesh will be in the opposite direction of the object. However, we still don't see the object being turned upside down. The cause is due to the activity and control of the visual nervous system.

Nearsighted eyes and old eyes Physics 9

What are called nearsighted eyes and what are called old eyes?

Nearsighted eyes

Characteristics of nearsighted eyes

Myopia in the eyes is certainly no longer strange to you. A clear, easy-to-recognize characteristic of nearsighted eyes is that nearsighted eyes cannot clearly see objects located at a distance but can only observe objects that are close.

Signs of nearsightedness

• Compared to normal eyes, nearsighted eyes have the far point (Cv) located closer.

• If the eyes are not adjusted, the eyes of a nearsighted person can only observe objects located at close range and will not be able to clearly see objects located far away.

For example:

• Students sitting in the classroom cannot see the lessons on the board

• Driving on the road cannot clearly see the content of advertising signs in the distance.

• It is impossible to read books if they are kept far away

How to overcome nearsightedness

There are 2 ways to overcome nearsightedness. Specifically:

• Method 1: Wear near-sighted glasses (diverging lenses) to help your eyes see objects in the distance clearly. Nearsighted glasses that match the nearsightedness of the eye will have the focal point F coinciding with the far point Cv of the eye.

• Method 2: Perform corneal surgery to change the curvature of the cornea.

Old eyes

Characteristics of old eyes

• His eyes are the eyes of the elderly, the elderly.

• His eyes can clearly see distant objects but cannot clearly see objects close to his eyes.

Signs of old eyes

• People with presbyopia can see distant objects clearly but cannot see objects close to their eyes clearly

• Compared to normal eyes, the near point Cc of the old eye is farther away.

How to fix old eyes

To overcome old eyes, you need to wear glasses (converging lenses) to help your eyes see objects clearly at close range.

Attention:

• Because it is a converging lens, when wearing glasses, the image of the object created by the glasses will be larger in size than the object but located farther from the eye than the object.

• In addition, due to wearing contact lenses, the image of the object on the retina is still the same size. Therefore, when wearing glasses, the eye will see images of objects of the same magnitude as when not wearing glasses.

See more: Understand what a magnifying glass is, its structure, uses & image creation in the most detail here

Some exercises on eyes, nearsighted eyes and old eyes Physics 9

Below are some self-practice exercises related to the knowledge about eyes, nearsighted eyes and aging eyes that you have just learned. Doing these questions will help students remember the lesson in the best way.

Question 1: When observing an object clearly, in which part of the eye is the image of that object located?

A. Vitreous body

B. Retina

C. Pupil

D. Black heart

Answer: B

To see an object clearly, the image of that object (through the lens) must lie on the retina of the eye.

Question 2: In terms of optics, the lens of the eye is considered one:

A. Convex mirror

B. Concave mirror

C. Converging lens

D. Diverging lens

Answer: C

The lens functions as a converging lens, with variable focal length.

Question 3: A pen is placed within Tam's field of vision. When Tam observes that pen, what are the characteristics of its image on the retina of the eye?

A. It is a virtual image, smaller than the object and in the opposite direction to the object

B. Is a real image, smaller than the object and in the same direction as the object

C. Is a real image, larger than the object and inverted to the object

D. It is a virtual image, larger than the object and in the same direction as the object

Answer: A

Because the eye's lens functions as a converging lens and the image of the object is behind the lens (collected on the reticular membrane). Therefore, the image of an object through the lens has the property of being a virtual image that is smaller than the object and in the opposite direction to the object.

Question 4: What is the expression of the old man's eyes?

A. Only see clearly objects close to the eye, not objects far away from the eye clearly.

B. Only see clearly objects that are far away from the eye, not objects that are close to the eye.

C. Can see objects clearly in the range from the near point to the far point.

D. Can't see clearly objects that are far away from the eyes.

Answer: B

His eyes have a near point Cc that is farther away than normal human eyes. Therefore, his eyes can only clearly see objects that are far away from his eyes, but cannot clearly see objects at close range.

Question 5: In order for the image of an object to be observed to appear clearly on the retina, how does the eye adjust?

A. Change the distance from the vitreous body to the reticular membrane.

B. Change the diameter of the pupil

C. Change the focal length of the lens of the eye.

D. Change the focal length of the lens and the distance from the lens to the reticular membrane.

Answer: C

The human eye can adjust the curvature of the lens to change the focal length of the lens. The distance from the lens to the retina is not adjustable.

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Question 6: When talking about eyes, which of the following statements is true?

A. The far point is the farthest point at which the eye can see clearly when placing an object at which the eye has the strongest adjustment.

B. The near point is the closest point where an object can still be seen clearly when an object is placed there.

C. Cannot observe objects when placed at the far point of the eye.

D. When observing objects at the extreme near point, the eyes must adjust the most.

Answer: D

The far point Cv is the farthest point where the eye does not have to adjust when placing an object there. The near point Cc is the closest point that the eye can see clearly, when the eye needs to adjust the most strongly.

Question 7: To overcome aging eyes, we need to wear glasses with properties such as:

A. Converging lens

B. Diverging lens

C. Convex mirror

D. Concave mirror

Answer: A

To overcome presbyopia, we need to wear glasses with properties like converging lenses.

Question 8: Spectacles can overcome nearsightedness because:

A. Create virtual images outside the eye's clear vision.

B. Create virtual images within the eye's clear vision.

C. Create real images beyond the eye's clear vision.

D. Create a real image within the eye's clear vision.

Answer: B

Nearsighted glasses are diverging lenses. When using nearsighted glasses, nearsighted glasses will create virtual images within the range of human vision.

Question 9: The mind can only clearly observe objects that are 1 meter or less away from the eyes. What's wrong with Tam's eyes?

Answer: Tam's eyes are nearsighted.

Because Lan's far distance Cv is 1 meter, much smaller than the normal human eye. Therefore, Lan has nearsightedness

Question 10: A person's eyes can only clearly observe objects located 90cm or more away from the eyes. What eye problem does this person have and what kind of glasses should be worn to correct it?

Answer:

• This person's eyes have presbyopia because his eyes can only clearly observe objects that are 90cm or more away from his eyes, so the near point Cc of his eyes is 90cm. The near point of the eye is larger than the near point of a normal person, so this person's eye has presbyopia.

• To overcome the eye problem, this person must wear glasses, which are converging lenses with a focal length of 90cm.

Question 11: A person's eyes can only clearly see objects located at a maximum distance of 120 cm from the eyes. What is wrong with that person's eyes? To observe extremely distant objects without having to adjust the eyes, what glasses does this person need to wear and what is the focal length?

Answer:

• Because that person's far point Cv is much smaller than that of a normal person, that person's eyes are nearsighted.

• In order to see objects that are extremely far away without the eyes having to adjust, that person must use glasses that are diverging lenses, with a focal length of 120cm.

Question 12: An elderly person must wear glasses with a converging lens with a focal length of 110 cm to be able to clearly see objects 30 cm away from the eye. Can you tell me what eye defect that person has? When not wearing glasses, at what distance can a person see clearly the objects closest to the eye?

Answer:

• This person's eyes are presbyopic.

• When wearing glasses, a converging lens with a focal length of 110cm, this person will be able to see objects located 30cm away from the eye. Therefore, an object 30cm away from the converging lens produces an image located exactly at the near extreme of the human eye.

Let f be the focal length of the lens, d be the distance from the object to the lens, d' be the distance from the image to the lens.

Applying the converging lens formula to virtual images, we get:

1/f=1/d-1/d'

1/d' = 1/d-1/f=1/30-1/110=4/165 => d'=41.25 (cm)

So that person's nearsightedness is equal to 41.25cm, or when not wearing glasses, he or she can clearly see the nearest objects at a distance of 41.25cm from the eye.

Conclusion:

Through the above article, timhieulichsuquancaugiay.edu.vn has compiled the most necessary knowledge related to the structure of the eye, the characteristics of nearsighted eyes and old eyes. Hopefully you can follow and accumulate more useful information, improving your own learning results.

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