The harder the better, the more the better!

Senior two physics competition questions are as follows

Match point 1? refraction law

Example 1 As shown in the figure, a semicircular glass is dug on the glass brick. If a beam of light passing through the center of the circle hits the glass brick, the correct light path diagram is ().

Answer?

B

C

D

A beam of light hits the hemisphere through the center of the circle, which coincides with the normal of the interface. Its incident angle and refraction angle are equal to 0, and its propagation direction remains unchanged. After reaching the glass, it will continue to spread in a straight line in the same medium; Seen from glass, light enters from a medium with low speed of light into a medium with high speed of light, so refracted light should be far away from the normal.

Standard solution a

If the interface between two media is a surface, its normal should be perpendicular to the tangent plane of the surface, that is, the tangent of the surface first passes through the incident point, and then the perpendicular to the incident point is the normal of the surface. If the surface is a circular surface or spherical surface, the normal is the radius of the circular surface or spherical surface passing through the incident point, so the light passing through the radius of the circular surface or spherical surface enters another medium, and the propagation direction remains unchanged.

A similar extension is shown in the figure. Rectangular glass tiles are cut into the shape shown in the figure.

After a certain distance, the light parallel to the main optical axis enters from the left and then from the far right.

The light emitted ()?

A. Keep the parallel light. B. It must be parallel light

C. it must be gathering light? D. the conclusion is related to D. all the above conclusions are possible

Match point 2? Optical refraction imaging and image application

Example 2 As shown in the figure, a cubic glass brick A and a hemispherical glass brick B made of the same kind of glass are placed on a newspaper. If the sides of cubes are the same as the radius of the hemisphere, they will be drawn from the top.

Looking down at the direction of the dotted line (centerline), the text is aligned with the centerline ()?

What is seen in a, a and b is higher than the actual one.

What you saw in B.A. was higher than what you actually saw. What you see in B is lower than what you actually see.

What you see in C.A. is higher than the reality, and what you see in B. is as high as the reality.

What you see in D.A. and B. is the same height.

Related skills? Looking down from the top of the hemispherical glass brick B, the center line is aligned with the characters in the direction of the dotted line (center line) in the figure. The light reflected by the characters passes through the center of the sphere and propagates along the normal line when entering the glass. The propagation direction of the light remains unchanged, and the intersection point of the reverse extension lines of the light is still at the characters, and the position remains unchanged. However, except for the vertical line, the light reflected by the figure under the cubic glass brick A is obliquely incident into the glass brick and will be refracted at the interface. The intersection of the opposite extension lines of refracted light is the image of the character, which is higher than the position of the character.

Standard solution c

Looking at the object below through the glass, you can see the image of the object, and you can determine the position of the image by making a light path diagram. The degree of dislocation between the image and the object is related to the thickness of the glass. This problem is a special case. Through the hemispherical glass brick b, you can't see the text with the center line aligned, but you will see it is higher than the actual one.

Xiao Ming, who is cautious in similar development, noticed such a phenomenon: if you open the window and look directly at the overhead wires in the distance, the wires bend down regularly; And if you look through the window glass, although the whole wire is arc-shaped, there are obvious irregular bends in different parts of the wire. When the head slightly swings to move the line of sight, the scene with irregular bending on the wire also moves. The main reason for this phenomenon is ().

A. Different parts of glass have different degrees of light absorption.

B different parts of the glass have different degrees of light transmittance.

C. Different parts of the glass have different thicknesses.

D. Different parts of the glass reflect different light.

Example 3 As shown in the figure, there is a luminous point A 1 above the water surface and another luminous point A2 in the water. When people see A2 in the air, it is the position of the image of A 1 in the water. Draw:

The light emitted by (1)A 1 is reflected by the water surface and enters the human eye path map.

(2) Optical path diagram of light emitted by 2)A2 entering human eyes

? first

?

second

Topic-related skills: First, use the imaging characteristics of a flat mirror to make A 1 symmetrical point about the water surface, that is, the image A 1' reflected by A 1', and then connect the eyes with A 1' to make the reflected light Ob. The intersection with the interface is the incident point o, and connecting A 1O is the incident light. Because the position where people see A2 in the water in the air is the position of A 1 in the water, and a 1' is also the position of the virtual image where A2 refracts through the water surface, OB is also refracted light, and connecting A2O is incident light.

The standard solution is shown in figure B.

There are two ways for eyes to draw the image of an object in water: one is to directly use the refraction law to make the approximate position of the image; Second, when the position of the image is known, the accurate optical path diagram of the image can be made. By connecting the image with the eyes, we can get the refracted light and the incident point, and then connecting the object with the incident point, we can get the incident light. Pay special attention to the direction of light propagation when painting, not from eyes to objects.

A similar extension is shown in the figure. Xiao Ming stood on the A side of the swimming pool, and saw that the image of street lamp B in the pool water coincided with a fish in the pool he saw at point C. The position of street lamp B and the approximate position of fish were determined by optical drawing.

Match point 3? Dispersion of light and refraction of colored light

Inspired by the dispersion phenomenon of natural light caused by prism, some researchers found that the focal position of convex lens is slightly different under the illumination of red light and blue light, as shown in Figure 3-6 (point A and point B in the figure). According to your analysis, the focus position of red light and blue light in the picture should be _ _ _ _ _ _ _.

To be fair, after natural light is refracted twice by the prism, a colored light band is obtained on the screen, which is red, orange, yellow, green, blue, indigo and purple from top to bottom. This phenomenon shows that the same prism has different refractive power for different colors of light, weak refractive power for red light and strong refractive power for purple light. If it is a convex lens, its convergence ability to purple light is stronger than that of red light, so it is purple light.

Standard solution b, a

The degree of refraction of light depends not only on the medium, but also on the type of colored light. Different media have different degrees of refraction to the same color light, and the same media has different degrees of refraction to different colors light. The dispersion of light is to use this principle to separate different colors of light in natural light.

Similar expansion At noon on May 17 this year, some citizens in our city saw the sun.

There is a colorful "halo" around, as shown in the picture, which is "solar halo". This astronomical phenomenon was formed.

The important reason is the scattering of sunlight through countless small ice crystals, in which all kinds of light are red.

Orange, yellow, _ _ _ _ _ _, blue, indigo and purple are arranged in turn, indicating sunshine.

Yes _ _ _ _ (fill in "monochromatic light" or "polychromatic light").

Match point 4? The color of the object seen by the eyes.

Example 5 When processing black-and-white photos in a darkroom, the safety light used is red, and the liquid column of the thermometer used is blue, not red. The following statement is correct ().

A. The darkroom safety light is red, so everything looks red. The red liquid column of the thermometer is not easy to see clearly in this environment.

The blue liquid column of the thermometer is black under red light.

C. The blue liquid column can be seen more clearly under red light.

D. the red liquid column reflects white light under red light.

The red safety light emits red light, while the blue liquid column only transmits blue light and absorbs other colors. So when the red light shines on the blue liquid column, the liquid column of the thermometer absorbs the red light, and no light from the thermometer enters the eyes, so it should be black.

Standard solution b

Let's use this topic to talk about the color of an object. Refers to the color of an object that people see when sunlight shines on it. We call the color at this time the "true color" of the object, but if the irradiated light is not natural light but colored light, the object will not reflect or transmit its true color light at this time, so the color of the object people see is not only related to the true color of the object, but also related to the light source that illuminates the object. When other true-color objects are irradiated with light of one color, the light of that color is absorbed. Everything people see is black. When black objects are illuminated by light of one color, the objects they see are black. When a white object is illuminated by light of one color, the color of the object they see is consistent with the color of the light of that color.

Similar development uses a pen that can write the scarlet letter to write a line on a piece of white paper, then the following statement is correct ()

A. This line of words on white paper will absorb the red light in white light in the sun, so this line is red.

B this line of words on white paper will reflect the red light in white light in the sun, so this line of words is red.

C This line on white paper is red, because it can emit red light.

D this line of words on white paper will be green if it is only illuminated by green light.

Match point 5? scatter

Example 6? Sandstorm is a bad weather phenomenon formed by land desertification. When the sandstorm happened, the visibility was only tens of meters, and the sky turned yellow and dark. The reason for this phenomenon ()

Only a part of light with longer wavelength can reach the ground.

Only a part of light with shorter wavelength can reach the ground.

C. Only a part of light with higher frequency can reach the ground.

D only a part of high-energy light can reach the ground.

This is the phenomenon that light is scattered by air and dust. Air molecules and dust scatter more light with shorter wavelength, and the scattered light returns to the air, leaving red light, yellow light and orange light with longer wavelength on the ground, so the sky turns yellow and dark when sandstorms occur.

Standard solution a

The phenomenon that light is scattered by air molecules and dust in the air when it propagates in the atmosphere is discussed. Light with shorter wavelength is easy to be scattered, while light with longer wavelength is not easy to be scattered, and their penetration ability is stronger. Therefore, red lights are used for the lights that are forbidden to pass, and yellow lights are used for the fog lights of cars, because they travel farther than lights with shorter wavelengths in the weather with low visibility, which is convenient for drivers to find them early. The relationship between wavelength and frequency of light is: light with longer wavelength. Light with short wavelength has high frequency and high energy.

When a similar extended cigarette is lit, the emitted smoke looks blue, because ()

A. the smoke particles themselves are blue.

B Smoke filters out other colors of light, and only blue light passes through.

C. smoke particles strongly scatter blue light.

D, the smoke particles emit blue fluorescence after absorbing light.

Reference answer 1. C As can be seen from the figure, after the rectangular glass brick is cut, the left piece can be regarded as a concave lens and the right piece as a convex lens. Concave lenses can make light diverge, and convex lenses can make light converge. When d=0, the virtual and real focal points coincide, parallel light enters and parallel light exits; When d > 0, the light converges, as shown in figure 2.c? 3. as shown in the figure? 4. Green multicolor light? 5.b？ 6.C