Junior 2 Physics Unit Test 15, Junior 2 Physics Test

omg!Do you have to find a textbook for the second year of junior high school for this topic?

Because the bottle is airtight, poured cold water, the air pressure in the bottle will decrease, the boiling point of water at room temperature and pressure is 100 degrees Celsius, but the air pressure is low, the boiling point will be low. For a low boiling point. The temperature of the water has reached the boiling point, and the object is amplified.

It refers to the convex lens into a virtual image. You look with your eyes. Your eyes are in front of the focal point, and what you see is an imaginary image.

Think it's big. But if you look a little farther away, you will see that the object is turned upside down, because after the focal point, the image becomes real. Eyes can't see clearly.

You use a piece of paper or a curtain to influence it. It's big and it's going to shrink. That depends on how you look at it.

When you blow it, there will be wind. The air pressure around the ball is small, while the air pressure is high where the wind is small. It will hold the ball, for example, you will see the safety line on the platform of the train station, and the wind will be generated when the train is moving.

If out of the security line. There is a possibility that you may be sucked in and have an accident, which is the same as this.

(1) During the watering process, the air pressure in the bottle decreases, and the boiling point of the water also decreases, and the water boils again. (2) Because the sound emitter is vibrating, the person dances in ** (3) Through the magnifying glass, the object is only proportionally magnified, and when the object is outside his 2 times the focal length, the object is shrinking, (4) The pressure is small where the flow velocity is large in the fluid, and the funnel is pushed up without falling under the action of atmospheric pressure.

Solution: (1) add cold water to the bottom of the bottle, the air pressure in the bottle decreases, so that the boiling point of the water decreases, and the water does not need to be 100 degrees to boil, (2) the sound causes the vibration of the paper, so that the villain beats, (3) it will not, sometimes it is magnified, but sometimes it will be inverted and reduced, (the object distance is greater than the focal length) (4) the flow rate of the internal air is fast, the air pressure is small, there is a pressure difference between the top and bottom of the ball, and the pressure below is large.

Handkerchiefs that don't burn out.

A handkerchief that has been burned by fire is still intact?

Experiment: Put the cotton handkerchief into a solution of 1:1 with alcohol and water to soak it, then squeeze it gently, clamp the two corners of the handkerchief with two crucible pliers, put it on the fire and light it, and when the flame decreases, quickly shake the handkerchief to extinguish the flame, which will find that the handkerchief is still intact.

Principle: When burning, the flame of alcohol is outside the water layer, and the water adsorbed in the fiber void absorbs the heat of combustion and evaporates, and the temperature on the handkerchief cannot reach the ignition point of the fiber, so the handkerchief is not burned.

Objects vibrate and make sounds.

Melting of crystals and amorphous.

The convergence of concave mirrors and the divergence of convex mirrors.

Friction generates heat. Imaging of small holes.

The effect of whether to add a lid on the boiling point of water Principle: When the container is covered and the water is boiled, the pressure will increase, resulting in an increase in the boiling point.

Equipment: Pressure cooker (the kind used in hospitals, with thermometer).

The Effect of Different Impurities on the Ice Melting Point: This is easy to do. Flour, milk, juice, and then ask the sanitation workers for snow melting agent, add water and stir well, put it into a disposable paper cup (don't use a glass or porcelain cup, it is easy to freeze and crack), and freeze it into ice cubes of the same size.

Put it in the refrigerator (with a glass door, look inside the refrigerator), slowly increase the temperature, and see which one melts first.

Characteristics of imaging wells of different shapes and sizes (small hole imaging);This one is best done. The candle is used as the light source (object), the cardboard is pierced with a small hole, and a piece of paper is used as the receiving screen. The whole experiment was to be done in a darkened room.

Concave lens imaging features;Similar to the previous one. Concave lenses can be used with the lenses of myopia lenses (must be myopia. Reading glasses are not concave lenses);A candle is used as a light source (object) or a small lamp to illuminate the cardboard with an arrow engraved, and a piece of paper is used as a receiving screen.

The whole experiment was to be done in a darkened room.

Measure the density of different fruits. 1. Fill the container (basin, pot) with water and weigh the weight m1 (you can use a weight scale), 2. Put the fruit (pineapple, apple, banana, orange) into the water to submerge it all (you can press it with chopsticks), so that part of the water overflows. Take out the fruit and weigh out the weight m2.

Fruit volume v = (m1-m2) p water, where p water = 1g cm, weigh the fruit weight m, then the density of the fruit p = m v

Different colors absorb heat. Fill the water in a disposable paper cup and freeze into ice cubes of the same size. Cover with cloths of different colors of the same texture, indoors, and see which one melts first, that is, which absorbs heat faster.

The cross-sectional area of the piston in the syringe can be calculated by dividing the volume of 20ml of the syringe by dividing it by the length of the graduated part, and the value of atmospheric pressure can be measured by dividing the tensile force by dividing by this cross-sectional area s.

Allow the air in the syringe to drain.

Don't know what to ask)

All sound-emitting objects are vibrating, and when the vibration stops, the sound stops, and the propagation of sound requires a medium, and the vacuum cannot transmit sound.

The loudness of the sound is related to the amplitude of the object, and the greater the amplitude, the louder the louder; The lower the amplitude, the less loudness.

The pitch of the sound is related to the frequency of the vibration of the object, and the higher the frequency, the higher the pitch; The lower the frequency, the lower the pitch.

The crystals absorb heat as they melt and the temperature does not change.

The liquid absorbs heat as it boils, and the temperature does not change.

When the crystals solidify, heat is emitted and the temperature remains unchanged.

Liquefaction releases heat.

Sublimation absorbs heat.

Ninghua wants to release heat.