A junior high school physics winter vacation homework question Hurry, Hurry

Because the temperature inside the mouth is higher than the outside of the mouth, if you put the small mirror directly into the mouth, the mirror will be stained with water vapor The purpose of baking the small mirror on the alcohol lamp is to increase the temperature of the mirror, so that the temperature is close to the temperature inside the mouth, so that the mirror will not have water vapor and affect the effect of observation

Prevents water vapor from liquefiing on the mirror surface.

Because the temperature inside the mouth is higher than the outside of the mouth, if you put the small mirror directly into the mouth, the mirror will be stained with water vapor The purpose of baking the small mirror on the alcohol lamp is to increase the temperature of the mirror, so that the temperature is close to the temperature inside the mouth, so that the mirror will not have water vapor and affect the effect of observation

The temperature of the lens is increased to prevent the condensation of water vapor when the cold lens enters the mouth, so that the doctor can clearly see the teeth.

Applied physical knowledge: When a cold lens encounters hot water vapor, liquefaction will occur on the lens to form "small water droplets."

Let the temperature of the small mirror rise, so that the water vapor in the patient's mouth will not liquefy when it encounters the mirror, so that the doctor cannot see clearly.

The purpose is to increase the temperature of the mirror and prevent the water vapor in the mouth from liquefiing into small droplets on the mirror when it is cold

You didn't listen to the lecture properly, the teacher should have talked about it

Alcohol evaporates quickly and exothermic, making the mirror hot. The water vapor exhaled from the mouth does not liquefy quickly, leaving water droplets on the mirror.

Prevent water vapor from liquefiing when it encounters a cold mirror and cannot be seen clearly.

Prevent water vapor from liquefiing the mirror and making it difficult to see.

Prevents water vapor from liquefiing on the mirror surface.

Because the boiling water temperature is 100 degrees Celsius, and the ice water mixture temperature is 0 degrees Celsius.

The 95-5 = 90 scales of the original thermometer is equivalent to an accurate 100 scales.

Then one scale of the original thermometer is an accurate 10 9

If the thermometer is hung on the classroom wall and its indication is 32 degrees Celsius, it will be 32-5 = 27 scales on an accurate thermometer.

Then the actual temperature is 27*10 9=30 degrees Celsius.

Happy learning.

When 95 grids are displayed, it is actually 100 degrees, and when 5 grids are displayed, it is actually 0 degrees, that is, 90 grids on the thermometer, which should actually be a change of 100 degrees, so each grid is 100 90 = 10 9 degrees of change, so from 5 to 32 there are 32-5 = 27 grids.

There should be a change of 27*10 9=30 degrees.

Since 5 blocks is 0 degrees, the answer is 30 degrees.

Boiling water 100 degrees, ice water mixture thing 0 degrees, 95-5 = 90 degrees, 90 divided by 100 = degrees, indicating that this thermometer is a degree, actual.

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 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.

If the driver is driving at high speeds, the front wheel should roll over, and if the rear wheel is braked, it should be fine.

The train only brakes the head of the car at high speed and the car behind it will rush to the front of the car and cause an accident, because the front car brakes and stops, while the car behind still maintains its original speed.

1.Front wheel locked: Direction out of control. Rear wheel locking: Tail flick occurs. Generally, the braking force of the front wheels is slightly greater than that of the rear wheels when the car is designed, because the consequences of accidents caused by tail flicks are more terrible.

The front wheels are used to control the direction, and if the front wheels are locked, you can't control the direction.

The rear wheels are used to drive, and if the rear wheels are locked, they will drift, and if the front wheels are not well controlled, they will flick their tails.

2.How many wheels the train car has, I want to choose by the length of the car. The driving wheels of the train are at the front of the locomotive mainly because the train has a track and does not need the front wheels to control the direction. Train brakes should also be used together with front and rear brakes.

Solution: (1) When the front wheel is braked, it cannot be steered, and the rear wheel is still running, which will be dangerous.

It would be much better to brake the rear wheels.

2) In order to brake the train, it is necessary to brake both the head and the tail. Because the mass of the train is so large, it needs to be two-pronged.

The front and rear wheels of the car brake together mainly to increase friction and make the car stop quickly!

The train brakes are all braked, and the purpose is the same as that of the car!

Solution: Set the steel pipe to be x meters long.

Then: x 340-x 500=

Get x = m. Answer: Let the oak beam to Tanzhou less long rice.

Solution: Let the speed of the car be V

The distance traveled by the car is s1=vt=v

The distance traveled by the sound s2=v sound t=340m s is known by s1+s2=2 440m=880m then v

v=12m/s

The speed of sound propagation in the air is 340 m s in (15 in the air).

340 meters.

440 2 = 880 meters.

30 meters. As a result, the car was launched at a speed of 12 meters per second.

The speed is 550

440 multiplied equals 1100

1100 is also divided by 2 to equal 550

Solution: Let the speed of the car be xm s.

According to the title: solution: x=12m s

The speed of sound in the air is about 340 meters per second.

Let the speed of the car be x meters and seconds, and the speed of the known sound v1 = 340 meters and seconds, t = seconds.

According to the formula s=vt, the solution is x=12 msec.

The speed of sound propagation is 340m s

The journey of sound is:

Sound distance from the cliff: 850-440=410m

Car driving distance: 440-410=30m

The speed at which the car travels: 30