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Bài 5. Hướng dẫn THTN mô phỏng mắt

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Nguồn: Sưu tầm
Người gửi: Lê Thái Trung (trang riêng)
Ngày gửi: 13h:08' 02-07-2008
Dung lượng: 664.5 KB
Số lượt tải: 17
Số lượt thích: 0 người

OCULAR ACCOMMODATION
(P 35 01)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20 W
1

POG 462
Diaphragm 3 and 5 slits
1

POG 251
Semicircle, lens model
1

POG 240.02
Plan-convex, lens model
1


Connecting lead
2

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler
1


The lamp with the diaphragm inserted is placed near the left-hand edge of the panel, arranging it so that the middle light ray is projected horizontally across the panel. This ray serves as the optical axis and is drawn in. The pin in the lamp is pulled out, creating three divergent rays of light.
The semi-circular object serving as a convex lens is placed at a distance of 33 cm from the light and symmetrical to the optical axis.



The light source symbolizes an object point and the semi-circular object the eye lens. The eye lens focuses the light rays at focal point F, symbolizing the eye`s "yellow spot".
The "model of the eye" is drawn in. At the position shown the eye sees the object sharply.



The light is moved toward the model of the eye, thus decreasing the object distance. Instead of seeing a sharp image point, a light spot on the retina results and the eye perceives the object unclearly since its image is not focused.


In a case like this the eye increases its power of refraction by increasing the curvature of the lens. In the experiment this is simulated by adding the planoconvex lens. The object is once again projected onto the retina sharply.







































FAULTY VISION AND ITS CORRECTION –
NEAR-SIGHTEDNESS
(P 35 02)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20 W
2

POG 462
Diaphragm 3 and 5 slits
2

POG 251
Semicircle, lens model
1


Connecting lead
4

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler
1


First, an optical axis is drawn in.
Two lights with diaphragms having slits are arranged symmetrical to the axis as shown in the diagram. A total of six light rays parallel to the axis are generated.
The semi-circular object serving as the eye lens is placed at a distance of 30 cm from the lamps. The light rays proceeding from a remote object are focused at point F on the retina in the case of an eye with normal vision. The object is sharp at this point.



A near-sighted individual`s eye is too elongated. This is symbolized in the experiment by drawing a more sharply curved line (at a distance of about 23 cm from the eye lens as shown in the diagram). A light spot results in the place of the image point and the near-sighted eye sees only a blurred object.



This faulty vision is corrected by eyeglasses consisting of concave lenses. In the experiment this is symbolized by placing a planoconcave lens in front of the model of the eye as shown in the diagram. The planoconcave lens disperses somewhat the light rays which travel almost parallel to the axis. The lens system consisting of a concave lens and the eye lens corrects the position of the image point so that it is projected upon the retina.










































FAULTY VISION AND ITS CORRECTION –
FAR-SIGHTEDNESS
(P 35 03)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20 W
1

POG 462
Diaphragm 3 and 5 slits
1

POG 251
Semicircle, lens model
1


Connecting lead
2

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler
1


The light is equipped with a diaphragm with three slits and placed near the left-hand edge of the panel so that the middle light ray is projected across the panel horizontally. This serves as the optical axis. The semi-circular model representing the eye lens is placed 26 cm from the lamp. The divergent light rays proceeding from the object point are focused at image point F located on the eye`s retina. The eye possessing normal vision is drawn in.



As compared with the eye having normal vision, a far-sighted eye is too short. A model of a far-sighted eye is drawn in as shown in the diagram. The object point is not projected sharply onto the retina, but rather as a light spot.



Applying a convex lens as an eyeglass increases the power of refraction of the lens system consisting of eyeglass and eye.

In the experiment this is simulated by placing a planoconvex lens directly in front of the semi-circular model.
The object is now projected onto the retina as a precise image point.

 
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