The mystery of physics experiments in the second year of junior high school, and the exploration que

1.Because the boiling point of oil is higher than that of water, when it touches water, it immediately evaporates the water on the surface, and the rapid evaporation of water produces a thrust on the oil, so the oil splashes; Or is it because the boiling point of oil is higher than that of water, the temperature that can be reached is higher, and of course it cooks faster.

2.First, if your hands are wet with water, they will play a role in lubrication, so they will not stick to the steamed bread. Second, the water is cold. Protect your hands from burns.

3.Using the same force, make the two eggs turn on the table, and it will be found that one of the eggs spins faster than the other, the fast spinning is the cooked egg, and the slow spinning is the raw egg. Because cooked eggs are solid inside, they will rotate with the shell, and raw eggs are like turning a glass of water with water when you rotate hard, and they store less kinetic energy than raw eggs.

4.The thermal conductivity of ceramics is much smaller than that of metal, the main purpose is to avoid the soup hurting our lips when drinking soup, the thermal conductivity is about large, the more obvious the feeling to the human body, just like the difference between wood and metal in winter, the metal will be more prickly.

5.This is due to the refraction of light, which is explained in detail in textbooks.

6.As the stove heats up, the water in the pot and the dumplings slowly heat up. We know that hot objects are meant to expand.

Dumplings and water are no exception. However, the degree to which an object expands by heat is different, with some things expanding quickly and others expanding slowly. Dumpling fillings and wrappers expand faster than water, and their volume easily increases considerably.

Hot dumplings are indeed swollen and filling, much larger than raw dumplings. However, because the weight of the dumplings did not increase, the volume increased. According to Archimedes' principle, since the dumplings are larger, the weight lost in the water is also larger, that is, the buoyancy of the water on the dumplings is greater than that of raw dumplings.

Of course, it is not a problem to float dumplings with a larger buoyancy than the original to float the weight and volume. Therefore, the dumplings can only float when they are cooked, that is, after the dumpling filling and dumpling skin have fully expanded.

After boiling dumplings, put some cold water, the purpose of which is to keep the temperature in the pot high while not causing overflow when the stove fire is difficult to adjust (such as firewood, coal fire), and at the same time can replenish the water lost by evaporation. Keeping the temperature in the pot high is to cook the filling, and the heat transfer has a process of first outside and then inside, and the meat filling is generally more cooked than the dumpling skin, so it needs to be cooked for a few more minutes after the dumpling skin is cooked. In fact, when using controllable fire sources, such as natural gas, liquefied gas, and electric stoves, as long as the amount of water in the pot is sufficient, do not add water, turn down the fire source to maintain a slight boil, and keep it for a few minutes, the purpose of cooking dumplings can also be achieved.

Prevent the dumplings from being boiled, the filling is not yet cooked, and cold water is generally added after the water is boiled.

Hehe, some of your problems belong to physical problems, and some I don't feel very much, I'm just talking about my views and learning together.

1. Why does water splash when dripping into hot oil? Why do fried foods boil faster than water?

Because the gas point of the oil (i.e., the temperature at which the liquid turns into gas) is very high, the water will quickly turn into gas and splash when it enters the oil. Also due to the high gas point of the oil, the oil can be heated to more than 200 degrees, while usually the water is heated up to 100 degrees. So why fried food is faster than boiled;

2. Why do you take the steamed buns that have just come out of the pot with some water on your hands?

Because the temperature of the steamed bread just out of the pot is very high, it will be hot to take it directly, and on the one hand, the water will vaporize and absorb the heat, and the water will also absorb the heat when the water heats up, so that the temperature of the steamed bread in contact with the hand will not be hot;

3. Do you know how to distinguish between raw and cooked eggs?

Cooked eggs spin faster and raw eggs spin slower, depending on the nature of liquids and solids.

4. Why is it better to drink less soup with a porcelain spoon than metal?

Metals are toxic and not good for the body, which should be a biological or medical problem.

5. Why do the chopsticks that are inserted diagonally into the water look broken?

This is the refraction of light, that is, the deflection of light in the direction of light at the interface between water and air;

6. Why does the dumplings sink to the bottom first and then rise when boiling dumplings? Why do you add cold water during cooking?

This is the knowledge of buoyancy, at the beginning, the density of the dumpling is greater than the water and sinks to the bottom, and the gas inside the dumpling expands during the heating process, and the volume of the dumpling increases, so that the density is less than the water, and it floats up.

As for why cold water is added during the boiling process, I personally think that it is to prevent the water from boiling too violently and breaking the dumplings.

The above is just a personal opinion, welcome to exchange.

A ...In the experiment "Measuring the Resistance of a Small Bub by Voltammetry", the supply voltage remains constant and the rated voltage of the small bulb is .

1) After the circuit was turned on, Xiao Ming found that moving the sliding blade of the sliding rheostat reduced the resistance of the connected circuit, and the number of the voltmeter also became smaller. What do you think is a mistake in the connection of this circuit.

When Xiaohui connected the circuit and just closed the switch, it turned out that the small bulb was dimly glowing, and the ammeter and voltmeter had indicators, and no matter how to move the sliding blade of the sliding varistor, the indicators of the ammeter and voltmeter did not change. This is because

2) As shown in the figure above, when Xiaohua connects the circuit, she wants to make the resistance of the rheostat smaller when the sliding blade of the sliding rheostat moves to the right, please help her connect the physical diagram of this circuit with a pen line.

3) Xiaohua will measure the data and calculation results into the following **:

Number of experiments: 1 2 3 4

Voltage u v current i a

Resistance r can be concluded that the resistance of the small bulb when it emits light normally is to keep one decimal place).

4) Further analysis of the data in the above table shows that the resistance value of the filament is varied, and the reason for this phenomenon is also reflected in life. For example, the incandescent lamp at home burns off the moment the light is turned on.

Optionally "easy" or "not easy").

5) In physical experiments, data are obtained through multiple measurements, and some data are obtained through multiple measurements, and the average value is used to reduce the experimental error; Some of them obtain multiple sets of data through multiple measurements to find certain patterns. Which of the following experiments differs from the other three experiments in terms of data processing and analysis (

a.**Relationship between current and voltage in a conductor b**Relationship between current and resistance in a conductor.

c.Voltammetry measures the resistance d. of a fixed-value resistorThe relationship between the magnetic strength of the electromagnet and the current is studied.

Convex lens imaging.

When an object is outside of two times the focal length (u>2f), it becomes an inverted, reduced real image (image distance: f2f). Such as a slide projector.

3) The object is within the focal length (u

1) According to the data in the table, the mechanical efficiency of the inclined plane in the second experiment can be obtained = useful work total work 110% = gh fs 100% = self-envy calculation).

2) Analysis of the experimental data shows that he is the relationship between the mechanical efficiency of the inclined plane and the roughness of the inclined plane.

If the slope is smooth, the useful work is equal to the total attack (the optional is greater than the brother hole orange or equal to the fluttering spike).