Physics questions in the second year of junior high school are in a hurry to ask for homework, and g

Now put a certain amount of water in the graduated cylinder and write down the scale value;

When the thin copper wire is wound around a round bar, each circle of wire should be next to each other, and the width is about 1 2 mm, measure the exact length with a scale, and then divide it by the number of wound circles, you can get the diameter of the copper wire, and then you can calculate the cross-sectional area;

Put the copper wire into the graduated cylinder and record the new water surface scale value;

The difference between the two scale values is the volume of the thin copper wire, and then divide this volume by the cross-sectional area to get the length.

You can put the thin copper wire in a graduated cylinder with water.

Find the volume. Then use a scale to measure the cross-sectional diameter.

If it's too fine, just measure the two together).

Find the base area.

Then use the volume, the base area is the height, and the length is the length.

According to the volume is equal to the cross-sectional area multiplied by the length, as long as you know the volume difference, and the area.

1. Wrap a piece of copper wire tightly around the measuring tung and circle it n times. Measure the width a of so many turns of copper wire wound on the graduated cylinder, and the cross-sectional area of the copper wire is pi*a 2 4n 2

2. The method of placing copper wire with a graduated cylinder can measure the volume difference v

The length is: 4vn2 pia2

Put the thin copper wire in a graduated cylinder with water.

Find the volume of the thin copper wire wrapped around a round bar, each circle of wire to be next to each other, about a width of 1 2 mm, measure the exact length with a scale, and then divide by the number of wound circles, you can get the diameter of the copper wire, and then you can calculate the volume of the bottom area is high is the length of the cross-sectional area;

The conjecture is based on the fact that when the angle of incidence is large enough to a certain extent, the angle between the refracted ray and the normal will be greater than 90 degrees, which is impossible, so the phenomenon of total emission occurs, that is, no refracted ray appears.

It can pass through all colors of light, and it is transparent.

Red light shines on the green leaves, because the green leaves reflect green light and absorb other color light, so the green leaves look black Total reflection is that when the light is shot from the material with a large refractive index to the material with a small refractive index, when the angle of incidence is large to a certain extent, the refracted light will disappear, and only the emitted light will be emitted. Both the translucent film of glasses and the periscope of a submarine apply this principle.

1.Light no longer undergoes refraction When light is incident from water into air, the angle of incidence is less than the angle of refraction.

2.Transmission (The color of a transparent object depends on the color light that can pass through, because a colorless transparent object can transmit all the color light, so it has no color.) )

Total reflection, the angle of incidence is greater than the critical angle. It's a high school problem.

1,a (the light in the sky is blue after rain, so you need to filter out some blue light to adjust the **color) 2, blue only blue light can pass through.

3. Mixing (mixing of color and light).

4. Reflects most of the light and absorbs only a small amount. (It's like taking a piece of white paper to block the light, blocking most of it, and passing through a small part.) ）

1, A 2, Blue 3, Red Blue 4, reflects all color light.

The lens and magnifying glass of the slide projector are both convex lenses, and they can both form (magnified) images, but the difference is that the lens of the slide projector becomes a (inverted magnified real) image, and the magnifying glass becomes a (upright magnified virtual) image.

Place the object 25 cm in front of the convex lens, and see a real image on the light screen 18 cm away from the lens, then this image must be (inverted and reduced) image, nuo keep the position of the object and the light screen unchanged, to make the light screen into another real image, the convex lens should be moved in the direction of (object).

If an object is at a point other than the 5x focal length of the convex lens, it gradually moves to the focal length along the main optical axis, and the change in image is (a).

A from small to large B from large to small c unchanged d from small to large and from large to small.

A person can see an object because the object forms (c) on the retina of the eye

A A real image that is inverted to the real thing like the real thing B Enlarged upright virtual image C Reduced inverted real image D Reduced upright virtual image.

A ** is an image of the upside-down TV screen after the glass screen has been processed, then this glass screen is (convex transparency) mirror, this ** is (real) image (fill in the virtual or real), the distance between the TV screen and the glass screen should meet the condition that (more than double the focal length).

The peephole on the security door allows the people inside the house to see the scenery outside, but the people outside the house can't see the situation inside the house clearly. This device is equipped with a (convex) lens in the crack of the door, which is installed on the inside of the door or on the side near the inside

2.Electric heating has both positive and harmful sides, and it is important to prevent the harm it causes. For example, an exhaust fan is installed in an electric motor to speed up heat dissipation, and a tape recorder and television have a heat dissipation window on the case to dissipate heat.

3.In Shen Kuo's writings, there is the following passage: "The Fang family (referring to experts who are proficient in literature) sharpens the with a magnet, and they can guide, but they are often slightly eastern, not all southern."

The two important physical phenomena (or knowledge) involved in this passage are the existence of a magnetic field around the earth, the powerful effect of the magnetic field on the magnetic needle and the phenomenon of magnetization, the method by which the needle acquires magnetism is called magnetization.

1. Ohm's law;

2. Fan, heat dissipation hole;

3. Compass phenomenon and magnetic declination phenomenon, magnetization.

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1.The resistance of the small bulb is measured by r=u i; The electrical power is p=ui

2.fans, heat vents;

3.Geomagnetic field and magnetization, magnetization.

500 nm is equal to 5*10 -6 dm.

This square nanometer is equal to centimeters.

3 10 2 dm is equal to 3 * 10 10 nanometers.

500 nm is equal to 5*10 -6 dm.

This square nanometer is equal to centimeters.