"Eyes and Optical Instruments" Light and Eyes PPT Courseware

Description

"Eyes and Optical Instruments" Light and Eyes PPT Courseware

learning target

1. Understand the simple structure of the eye and the basic principles of eye vision

2. Understand that cameras are made using the principle that convex lenses can shrink the real image.

3. Understand the structure and function of microscopes, telescopes, etc.

4. Understand the causes of myopia and hyperopia and their correction methods through experimental simulations

Core test points: Application of lenses, causes and correction of myopia and hyperopia

Preview before class

1. The eyeball is like a camera, ______ is equivalent to a convex lens, which concentrates the light from the object on ______; the eye can see objects at different distances clearly by relying on ______ to change the curvature of ______ , thereby changing the focal length of this advanced camera lens.

The image of the ______ scene after passing through the lens cannot fall on the retina, but is located on the ______ of the retina. This is myopia; hyperopia can only see ______ objects clearly. When looking at nearby objects, the image formed after passing through the lens Like ______ falling on the retina.

3. Cameras are made using the principle that convex lenses can form ______, ______ real images. The lens of the camera is equivalent to a ______, and the photosensitive film in the cassette is equivalent to ______.

4. The microscope is mainly composed of two groups of ______, the objective lens and the eyepiece, through which a virtual image of the object ______ can be formed.

5. A telescope is mainly composed of two sets of lenses: ______ and ______. The virtual image of an object is observed through ______, as if the object is ______, so that we can see distant objects clearly.

Lectures in class

Knowledge point 1. The structure and imaging principle of the eye

(1) Structure of the human eye: cornea, ciliary body, lens, pupil, iris, vitreous body, retina, etc. As shown below:

(2) How the human eye sees objects: The lens and cornea of ​​the human eyeball work together like a convex lens whose focal length can be changed, and the retina is equivalent to a light screen. When the eye sees an object, the object is placed on the retina through the "convex lens" The result of forming an inverted and reduced real image. The optic nerve cells on the retina are stimulated by light and transmit this signal to the brain, and we see objects.

(3) Far point: The object is at different distances from the human eye. The human eye can automatically adjust the focal length of the "convex lens" through the tightness of the ciliary body so that the image falls on the retina. When the ciliary body is completely relaxed (the lens becomes the flattest and has the largest focal length), the location of the object that the human eye can see clearly is called the "far point" of the eye. The far point of the normal eye is at infinity, that is, from infinity The parallel light emitted by the object into the eye can be imaged on the retina.

(4) Near point: When the ciliary body is at its most tense (the lens becomes the most convex and the focal length is the smallest), the location of the object that the human eye can see clearly is called the "near point" of the eye. The near point of a normal eye is approximately 10 cm from the eyes. Therefore, the range that normal eyes can see clearly by their own adjustment is from 10 cm from the eye to infinity.

(5) Photopic distance: Under suitable lighting conditions, normal eyes will not feel tired easily when looking at objects 25 cm away from the eyes. Therefore, the distance 25 cm from the eyes is called photopic distance.

[Example 1] The light reflected from external objects enters the inside of the eyeball through the pupil, and then undergoes a series of refraction, and the object image is formed in ( )

A. Cornea B. Retina c. Lens D. Vision

【Exercise 1】 Regarding eyes, which of the following statements is incorrect ( )

A. Although the human eye is very complex, its principle is similar to that of a camera, in which the retina is equivalent to film.

B． The eye uses the lens and cornea to refract light and then image it on the retina.

C. When the ciliary body relaxes, the lens is thicker, and the light from distant objects just converges on the retina, so the eyeball can see distant objects clearly.

D． When the ciliary body contracts, the lens becomes thicker and its ability to refract light becomes larger. The light from nearby objects converges on the retina, and the eyes can see nearby objects clearly.

Knowledge point 2. Myopia and its correction

(1) Causes of myopia: The lens is too thick and the refractive power is too strong; or the eyeball is too long in the front-to-back direction, so the light from a distant point converges in front of the retina, as shown in Figure a, and has already reached the retina when it reaches the retina. It's not a point but a blurry spot. Therefore, myopic eyes can only see close objects clearly, but cannot see distant objects clearly.

(2) Correction: Taking advantage of the feature of concave lenses that can make light diverge, placing a suitable concave lens in front of the eye can make the light from distant objects converge on the retina. As shown in Figure b, people with myopia should wear concave lenses for correction.

[Example 2] Eyes are important organs of the human body. It is extremely important to understand and understand your own eyes, and to use and protect them scientifically. Student Wang Yan's eyesight defects were detected by the school doctor as shown in Figure A. The school doctor recommended that she wear glasses as soon as possible to correct them. Please draw the spectacle lenses that Wang Yan needs to wear in the box of Figure B based on Figure A.

[Exercise 2] (2014·Heilongjiang) Middle school student Xiao Ming found that he could only see nearby objects clearly recently, but could not see distant objects clearly. The teacher told him that he might be suffering from ______ (fill in "myopia" or "hyperopia" ) Eye disease requires correction by wearing _____ lenses.

Knowledge point 3. Hyperopia and its correction

(1) Causes of hyperopia: The lens is too thin, the refractive power is too weak, or the eyeball is too short in the front-to-back direction. Light from a nearby point reaches the retina before it converges to a point, as shown in Figure a. A blurry spot forms on the retina.

(2) Correction: Taking advantage of the feature of convex lenses that can make light converge, placing a convex lens in front of the eye can make the light from nearby objects converge on the retina. As shown in Figure b, people with farsightedness should wear convex lenses for correction.

[Example 3] (2014·Ningde) Glasses as shown in the picture ( )

A. It is a convex lens and can be used to correct farsightedness.

B． It is a concave lens and can be used to correct farsightedness.

C. It is a convex lens and can be used to correct myopia.

D． It is a concave lens and can be used to correct myopia.

[Exercise 3] (2014·Changsha) The picture shows the image of Uncle Yang’s eyes when looking at objects. The type of his eyes and the lenses that need to be corrected are ( )

A. Hyperopia convex lens

B． Hyperopia concave lens

C. Myopia concave lens

D． Myopia convex lens

Knowledge point 4. Prescription of glasses

The reciprocal of the focal length of the lens is called power, represented by Φ, Φ=1/f (f uses "m" as the unit), the unit of power is m-1, the power of the glasses is equal to the value of the power multiplied by 100: D= lOO·Φ=100/f (f uses “m” as the unit).

Note: The power of myopia lenses is negative, and the power of hyperopia lenses is positive. The greater the power, the more obvious the divergence effect of myopia lenses, and the more obvious the convergence effect of hyperopia lenses.

[Example 4] When Xiao Ming was in eighth grade, he was given a pair of -100-degree glasses at the Municipal People's Hospital. After entering ninth grade, due to heavy study tasks, he often felt that he could not see clearly what the teacher wrote on the blackboard. His father brought him After he went to the Municipal People's Hospital for an optometry, the doctor said that Xiao Ming needs to wear a pair of -300 degree glasses. Please help Xiao Ming analyze the following three issues:

(1) The glasses worn by Xiao Ming are lenses;

(2) What is the focal length of the new pair of glasses that Xiao Ming is wearing?

(3) Has Xiao Ming’s vision improved or worsened? What issues should he pay attention to in his future studies?

[Exercise 4] Xiao Ming’s grandfather has a pair of reading glasses. One day, Xiao Ming wanted to estimate the power of the glasses. He let a beam of sunlight shine vertically on the reading glasses and moved a piece of paper back and forth on the other side of the reading glasses. , find the smallest and brightest light spot, and measure the distance from the light spot to the reading glasses to be 20 cm. Then the power of this pair of lenses is ________, and the power of the lens is _________ degrees.

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Update Time: 2024-11-14

This template belongs to Physics courseware Guangdong and Shanghai version of eighth grade physics volume one industry PPT template

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