Junior high school science experiments, junior high school physics experiments

Electronic Components Demonstration Experimental Materials Resistors, capacitors, inductors, potentiometers, diodes, transistors, manifold blocks, etc. 81 Group Experimental Materials 8111 Junior High School Physics Group Experimental Materials Batteries, beads, wires, candles, lenses.

Please, can you send me a copy too? Mailbox.

There is no accurate answer to this, and it still depends on the accumulation of ordinary brushing questions, but the general ones I do are nothing more than that:

Biological: no control group was set; The experiment was only done once, the results were not accurate, and the number of tests was too small; The number of items (e.g. seeds) is too small and inaccurate; There is no exclusion of any factors and so on.

Physical: not controlling the same variable (what height, length, etc.); does not take into account the influence of what factors (friction, resistance, etc.);

Chemical: water, CO2, CO and other interferences are not excluded (this depends on the topic, usually the solution is to add a concentrated sulfuric acid or anhydrous copper sulfate or sodium hydroxide); No exhaust treatment was carried out (this is mainly for topics with CO); Poor sealing performance and so on.

It is recommended to read the experiments in the book directly, so that your accuracy rate is higher.

1.Perforated pieces of paper hold water.

As you know, anything with holes will leak. However, now you will see a thin piece of paper full of small holes, which can actually hold up a pound or even two pounds of water, without leakage.

1 Equipment A large empty bottle, a piece of paper with a large needle piercing many small holes, and a large glass of colored water.

2 Performance process.

Fill a large empty bottle with colored water; Cover the mouth of the perforated piece of paper and press the piece of paper with your hand, turn the bottle upside down so that the mouth of the bottle is facing down, as shown in the picture, and then gently remove your hand. The paper lid the bottle without moving, and the water did not come out of the hole.

When performing, it should be noted that the bottle should be a small-mouthed bottle (such as a large-mouth bottle, and the paper should be harder), and the fuller the bottle of water, the better the effect. After inverting the bottle mouth, the hand should be slowly and gently removed to avoid leakage of the paper without the lid being flat, or even the water from pouring out.

3 Explanation The thin piece of paper can hold the water in the bottle because the atmospheric pressure acts on the paper, creating an upward supporting force. The hole does not leak water because the water has surface tension, and the water forms a film of water on the surface of the paper, so that the water does not leak out. It's like an umbrella made of cloth, which doesn't leak rain even though it has many small holes.

Research question: Relationship between volume and temperature of alcohol.

Solid beam testing material: a bottle with a stopper filled with alcohol, a glass tube plugged into the bottle, and an alcohol lamp.

Experimental method: Slowly heat the bottle with an alcohol lamp and observe the change of liquid level in the tube.

Experimental phenomenon: the higher the temperature, the greater the height of the liquid level.

Experimental Analysis: The Principle of Thermal Expansion and Cold Contraction.

Experimental conclusion: The temperature of alcohol increases, and the volume increases, which can be seen that a thermometer can be made by using the principle of this oak friend annihilation.

I'm a column equation and see if the answer is the same as yours.

I assume that the iron mass in the original mixture is x and the copper mass is y

then divide each in half, with a mass of x+y 2

The insoluble substance after the anti-envy grinding should be the copper in the original mixture, and the sum of the copper that is replaced by the reaction of iron and copper sulfate, which is the gram.

The precedent reaction equation is Fe+H2SO4=FeSO4+H2 X

Calculate that x is a gram and a part of iron is a gram.

Let's take the equation x+y 2 + 64=, which is simplified: 23x+7y=

In column one: Simplify to 8x+7y=

Simultaneous and , solution x

Count it yourself later.

This question is very complicated, right, on the first floor, the title did not say that it was evenly divided into two parts, and the content of iron and copper in the same mass of the two parts was different, right?

Writing chemical formulas, typing is too wide, and the keys are troublesome, and I will talk to you about the ideas.

First of all, the production of hydrogen is entirely due to iron.

Therefore, by writing the chemical formula for the reaction of iron with filial piety and sulfuric acid, the mass of iron can be calculated, and *2 is the mass of iron in the mixture.

The second question is to write a formula for the reaction of iron and copper sulfate, and based on the iron data obtained above, you can calculate how much copper is born, and subtract it to get the same mass in the mixture.

Finally, the mass of copper (the mass of copper + iron) is done.

It shouldn't be put.

I don't know

But if it's emitting light on its own, it's a light source.

A light source is an object that emits light on its own.

A light source is an object that is emitting light, so it is a light source when it absorbs light and can emit light.