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Bài 3. Hướng dẫn THTN về hiện tượng khúc xạ ánh sáng

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Nguồn: Sưu tầm
Người gửi: Lê Thái Trung (trang riêng)
Ngày gửi: 13h:12' 02-07-2008
Dung lượng: 2.6 MB
Số lượt tải: 17
Số lượt thích: 0 người
REFRACTION OF LIGHT
(P 33 01)
Apparatus:
GSN 246
Adhesive Magnetic Board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 550.01
Cuvette
1


Connecting lead
2

KAL 60/5A
Power supply
1


Beaker glass
1

Procedure:
Fill the cuvette with water.
Setup the ray box as shown
A light ray emitted by the ray box hits the surface where the air meets the water at an angle of incidence of about 30°. It may, on the one hand, be observed that the light is refracted toward the perpendicular and, on the other, that it is partially reflected from this surface.
The light ray hits the surface where the water meets the air at an angle of incidence . It may be observed that the light ray is refracted from the perpendicular at angle and partially reflected at angle .The reflected ray of light returns to the surface where the water meets the air. Here again refraction from the perpendicular and partial reflection occur.
In addition, it may be seen that the ray proceeding from the light and the one leaving the cuvette below are shifted. The beaker with water represents a plate with parallel faces.








TOTAL REFLECTION IN WATER
(P 33 02)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 550.01
Cuvette
1


Connecting lead
2

KAL 60/5A
Power supply
1


Beaker glass
1




The cuvette is filled with water. The water may be colored using fluorescein sodium.
The transition from water to air is observed.
The angle of incidence is smaller than the critical angle for water. Thus, partial reflection (ray a) and refraction from the perpendicular (ray b) occur.

The ray box is turned so that the angle of incidence is greater than the critical angle for water.
No refraction occurs, merely complete reflection – total reflection.
The surface of the water acts as a mirror.































CALCULATING THE INDEX OF REFRACTION
(P 33 03)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 400.03
Optical disc
1


Connecting lead
2

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler
1


The ray box is placed so that the angle of incidence is 30°.
The angle of refraction is measured along with the distances x and y.
The experiment is repeated at an angle of incidence 1 = 60° and the corresponding results are noted:



x = 7,5 cm x1 = 12,9 cm
y = 5,1 cm y1 = 8,8 cm

The ratio of the two distances to each other is constant. This value is termed the index of refraction n.
It may be furthermore shown that:
sin 30° : sin = sin 60° : sin 1 = 1,47
It is not difficult to deduce from this the Law of Refraction: sin a : sin b = n

Using the equation 1 : sin = n the critical angle is found to be about = 43°, which matches up quite well with the results of the experiment.













































TOTAL REFLECTION IN GLASS
(P 33 04)

Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 400.03
Optical disc
1

POG 251
Semicircle, lens model
1


Connecting lead
2

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler
1


Setup the ray box and the semicircle lens model on the optical disk as shown.
The light ray emitted by the ray box is to be aimed directly at the center of the lens. This may be checked by means of the reflected ray.
The angle of incidence measured must correspond exactly to the angle of reflection measured.
The light ray hits the lens at an angle of incidence of 0at first. This light ray corresponds to the perpendicular which is drawn in.
Then the angle of incidence is set again to different values: 1 = 10°, 2 = 20° and 3 = 30°. The partially reflected rays are observed along with the refracted ones.


Angle of incidence 
10°
 20°
 30°
 40°
 43°
 45°
 50°
 60°

Angle of refraction 
18°
 23°
 47°
 75°
 90°
–
–
–

Dispersion - Ray brushes Total reflection
spectrum surface = 90°

At an angle of incidence of = 40° and an angle of refraction of about 75°, color dispersion may be clearly seen.

At an angle of incidence of about = 43° the refracted ray brushes the surface = 90°). Once the critical angle is reached, only the reflected ray remains – total reflection.
































TOTAL REFLECTION IN A SEMI-CIRCLE BODY
(P 33 05)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 400.03
Optical disc
1

POG 251
Semicircle, lens model
1


Connecting lead
2

KAL 60/5A
Power supply
1


The ray of light emitted by the ray box hits the acrylic glass object at a right angle. Due to total reflection, it then travels along the boundary between the acrylic glass and the air in a semi-circular direction through the object and leaves it at the bottom end (light beam, aperture angle). The aperture angle is determined by the manner in which the thin, slightly divergent light beam enters the object. The individual light rays follow slightly different paths through the acrylic glass object.

When the light ray is moved farther inside, the path of the light can be seen more clearly. The effect caused by total reflection along the surface where the acrylic glass meets the air can now be easily recognized.






BASIC PRINCIPLE OF A PHOTOCONDUCTOR
(P 33 06)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 240.03
C shaped lens, Photoconductor model
1


Connecting lead
2

KAL 60/5A
Power supply
1


The light ray emitted by the ray box hits the end of the C-shaped lens at a right angle. Due to total reflection, the light ray travels along the surface where acrylic glass meets the air.
The effect caused by total reflection along the surface where acrylic glass meets the air can be easily recognized.
Light can be transported in a thin glass body for long distances and even along a crooked path in such a manner. This is the basic principle of a photoconductor.
The refraction of the light ray away from the perpendicular can be observed where the light leaves the acrylic glass object.


















PHOTOCONDUCTOR, FLEXIBLE
(P 33 07)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 245
Fiber optic, model
1


Connecting lead
2

KAL 60/5A
Power supply
1


The model photoconductor is attached to the side of the ray box with fan and circular aperture. The light from the bulb is conducted along the flexible photoconductor for some distance and even along a crooked path.
The spherically shaped opening at the end of the photoconductor causes a lens effect resulting in a distinct light cone at the immediate end of the photoconductor.
With the aid of this photoconductor, light may be conducted into a small box for example.


















THE PLANE PARALLEL PLATE
(P 33 08)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 311
Prism, trapezoid
1


Connecting lead
2

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler



The light ray enters the surface of the trapezoid at a right angle, passes through the acrylic glass and leaves it without being refracted. This ray path is drawn in.
 
The trapezoid object serving as a plane parallel plate is brought into the second position as shown.

The following phenomena may be observed:
Reflection (light ray 1) and refraction toward the perpendicular occur where air and acrylic glass meet.
Refraction from the perpendicular occurs where acrylic glass meets the air. The light ray leaving the plane parallel plate is displaced yet parallel to the ray entering. Part of the light is reflected at point 2.
This reflected light ray is refracted from the perpendicular where the acrylic glass meets the air (light ray 2).

The two light rays travel parallel to each other.

The greater the inclination of the plane parallel plate, the greater the angle of incidence. The greater the angle of incidence, the greater the parallel displacement of the light ray which is refracted twice.










REFRACTION OF LIGHT IN A PRISM
(P 33 09)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 461
Diaphragm 1 and 2 slits
1

POG 310.03
Prism, right angle
1


Connecting lead
2

KAL 60/5A
Power supply
1


Whiteboard marker
1


Ruler



The prism with a right angle and equal sides is positioned as shown in the diagram.
At first refraction and partial reflection at the refracting surfaces can be observed.
The place where the light ray hits the surfaces is marked, and the outline of the prism and the position of the two perpendiculars are drawn in. This shows more distinctly the refraction toward the perpendicular where the ray passes from an optically less to an optically more dense medium and the refraction from the perpendicular in the opposite case.

The prism is then turned in a clockwise direction. The partially reflected rays become brighter and the refracted ray turns downward; deviation as a whole increases. The critical case is reached when the ray brushes the surface.














DEVIATING PRISM
(P 33 10)
Apparatus:
GSN 246
Adhesive magnetic board
1

POG 465
Ray box, 6V 20W
1

POG 462
Diaphragm 3 and 5 slits
1

POG 310.03
Prism, right angle
1

POG 220.01
Color filter red
1

POG 220.02
Color filter blue
1


Connecting lead
2

KAL 60/5A
Power supply
1


The prism with a right angle and equal sides is positioned about 20 cm from the ray box so that one of the shorter sides is perpendicular to the light rays reaching it.



The hypotenuse of the prism (boundary surface
 
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