Help solve the second year of junior high school physics questions, ask for answers, and ask for ans

Solution: Method: Submerge the same volume of iron and aluminum in water, respectively.

Steps: Use a spring dynamometer to measure the gravity of a solid iron block and a block of aluminum.

Submerge the iron and aluminum blocks in the water, respectively, to weigh their gravity in the water.

Calculate the buoyancy of iron and aluminum.

Object gravity The object is submerged in water by gravity buoyancy of the iron block

Conclusion: If the volume of the drained water is the same, then the buoyancy of the solid iron and the aluminum block are the same.

Conclusion of modification: If the buoyancy of the iron and aluminum blocks is the same, then the buoyancy of the object is independent of the density of the object. Question addendum: When the volume of drained water is the same.

Through the experiment**, the students already know that the buoyancy of an object immersed in a liquid is related to the density of the liquid. However, some students speculate that the amount of buoyancy experienced by the object may also be related to the density of the object. Please design an experiment to test this conjecture.

1) Existing equipment: spring dynamometer, thin wire, beaker, water, solid iron and aluminum blocks of the same volume (2) Design experiment: Xiaoli believes that when the buoyancy is large, the method of controlling variables should be used, because it is known that buoyancy is related to the density of the liquid, so they only use one liquid, how to make the volume of the discharged liquid equal?

Your method is: All of them invade the water 3) Write out the experimental steps: 1. Weigh the gravity of lead and iron balls; 2. The total induction into the water, the reading of the spring indication 3 phase subtraction to find the difference and buoyancy 4 difference are equal.

4) Design a record of data

5) Conclusion: If then the question is added:

1. Use a spring dynamometer to make the indication of each immersion of the metal ball in water equal.

When the object has a volume of 3 5 immersed in water in a container, the height of the water h=12cm. At this time, the volume of the object immersed in the water, that is, the volume of the object discharged from the water, v row = 3 5 10 = 600cm.

Multiply the height h of the water at this time by the area of the bottom of the container s to get the total volume in the container.

v total = v water + row = 12 200

2400cm³

Therefore, the volume of the original water in the container:

v water = v total - v row = 2400-600

1800cm³

The height of the water in the container when the object is not placed.

h'=v water s=1800 200

9cm。

As for the diagram in the question, there is a diagram and the solution is analyzed according to the diagram and the question.

d is correct.

As shown in Figure B, R decreases with the increase of natural gas concentration, so when the concentration of natural gas decreases, the resistance value of R increases, the total resistance increases, and the total current decreases, so the indication of ammeter A decreases, R0 is the constant resistance, when the current passing through him decreases, according to Ohm's law U=IR0, the voltage at both ends of R0 also decreases, so the number of voltage representations decreases.

The concentration of natural gas decreases, the resistance of the gas resistor r, the total voltage does not change, the current increases, the resistance value of r0 does not change, the voltage on r0 increases, the number of voltage representations increases, d, error.

When the concentration decreases, the gas resistor becomes larger, then the total circuit resistance becomes larger, the current becomes smaller, and then the voltage representation number decreases according to Ohm's law. d right.

The smaller the concentration, the greater the r. If the supply voltage does not change, the total resistance becomes larger, the A value becomes smaller, and R0 does not change, so V becomes smaller.

In series circuits, the greater the resistance, the greater the voltage, the concentration decreases, the resistance of r increases, and the voltage also increases, because of the series voltage division, so the voltage at both ends of r0 decreases,,,d is right, your satisfactory answer is wrong.

As the weather concentration decreases, the R-resistance becomes larger, the current decreases, the R0 resistance increases, and the voltage representation decreases.

Dispersion of light.

Experimental equipment: sunlight, water, deep basin, plane mirror.

Experimental phenomenon: The colors of the reflected light are red, orange, yellow, green, blue, indigo, and violet.

Conclusion: Proven"White light is made up of a variety of colored lights"。

A mirror in front of you, a mirror behind you, and the back of your head in the mirror behind you can see through the mirror in the front.

1. Equipment: beaker, water, two plane mirrors, and a light screen.

Steps: Fill a beaker with an appropriate amount of water, place a flat mirror diagonally in the water, and use another flat mirror to reflect the sunlight so that it is obliquely reflected from the surface of the water into the water, and when the light is reflected back by the plane mirror in the water, it is already separated.

Phenomenon: The light received on the light screen is a seven-color light band.

Conclusion: White light is composed of a variety of colored light.

2. Take two plane mirrors, one in front of you and the other behind you, but you must be a promising child, otherwise you won't be able to see the back of your head for the rest of your life!

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Question 10 B Because the person in the car sees that the raindrops are stationary, the raindrops and the car are relatively stationary.

Question: Doesn't it mean that the people in the car see the raindrops falling vertically, so shouldn't the rain be moving for the car?

The horizontal direction is stationary.

The vertical direction is in motion.

So it's diagonally eastward.

Question: What does the horizontal direction look like, and what is the vertical direction?

When we say that an object is relatively stationary, then its horizontal motion and vertical motion are relatively stationary with you.

Right? He does in general, the two of them have a relative motion, because the raindrops he has a descending process, but the rook he only has a lateral movement.

You can see the raindrops falling in the car because I'm still in the car, so the direction of the fall is relative.

And I didn't see which way the raindrops were falling in the car, they were vertical, and there were no leaves in the transverse direction, because it was in line with my speed in the transverse direction.

For example, if I sit in the car and I let go and throw something, he must fall down, because anything in the car, he is the same as me, and the horizontal direction is the speed of the car.

I can't understand the question, I can't understand it.

I'm not very good at asking questions, so I can't understand these sentences, but thank you anyway!

It's okay and you can continue to ask me questions.

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1.Equipment: prism, natural light source.

Steps: Shoot natural light in a dark environment like a prism, and the white light will be dispersed into 7 different colors.

Reason: Due to the different frequencies of different colors of light, the refractive index is different, resulting in dispersion.

Conclusion: White light is composed of different colors of light.

2.Two mirrors will do.

1.Experimental equipment: prism.

Step 1: Place the prism in the sunlight and let the sunlight shine through it.

Phenomenon and conclusion: The projection on a plane is a variety of colored light, indicating that "white light is composed of a variety of colored lights".

2.Two mirrors are sufficient, one in front and one behind.

Experimental equipment: light source, prism and light screen.

Experimental procedure: Place the light source on the prism and receive it with a light screen.

The second question can use two mirrors.

1：b。During the class, the teacher will ask that when measuring the object, the result will be accurate to the last digit of the index value, and the index value can be known according to the meaning of the question, so the answer is in the latter digit, so the answer should be accurate to two decimal places, **The answer can be known, only the B answer is compound to the question.

2: The mistake is that there are no units, which is a common mistake in junior high school physics. It should be written as: The smallest unit that should be written in is 1cm, so the graduation value should be. That's 1dm.

3:: When observing the scale is not perpendicular, it is a misoperation in the physical experiment, so it is not considered an error. b：

If the scale is not accurate, it is a problem with the equipment, or the equipment is not selected correctly, and it does not belong to the error range. D: The concept of error and error is vague, and error can be avoided, but error cannot be avoided, so the answer to D is an irregular use of language.

So according to the method of elimination, the C answer is correct.

4：c。Because the length of 100cm is 39cm, the desk occupies 39 of this ruler. So the length of the desk is 39 for the ruler. So use. Observe the answers. Answer c is the closest to the calculated value.

1. The units in the B answer are cm, and the minimum scale is 1mm, which means the exact value, and the reading must be estimated by one digit after the exact value, that is to say, the answer should be two decimal places, therefore, only B meets the topic.

2. The length of the blackboard should be an estimate, and the exact value is. So the error is that the length unit is not written, and such data is meaningless. The minimum division is 1 dm, which is 1 dm.

3. C (multiple measurements to reduce error) A The line of sight in the answer is not perpendicular to the wrong operation, not an error B The answer is wrong because the selected scale cannot meet the requirements, which is an error D Error can be avoided, but the error cannot be avoided.

4. The actual length of 1cm of the meter ruler is, and the measurement of the desk is 39cm, so the actual length of the desk is 39

Use the scale to be accurate to the next digit of the minimum scale, that is, the first question is selected b, the second question is not written in the unit, common sense should be, the minimum graduation value is the previous one) three questions choose b, measured three times in order to take the average value to reduce the error (this error is not an operation error, but an unavoidable error), can not avoid the operation error. The fourth problem is to multiply two numbers to choose c

1. b After the minimum scale value, one more person should be estimated. The minimum scale here is 1mm, so it should be estimated.

2. There is no unit The minimum scale is. Same reasons as above. One more point is estimated after the minimum tick value. It's accurate here, so the minimum scale is.

The rest is ditto.

1. b The recording result should be recorded to the next digit of the graduation value, the millimeter scale should be recorded to the next digit of the millimeter, if the centimeter is used as the unit, there are two decimal places after the decimal point.

2. There is no writing unit or decimeter. You can record the result as a value with only one decimal place, and the unit with it is the graduation value.

3. C Errors are avoidable, but errors are unavoidable.

4. The scale used in d is larger than the standard scale, and the measured value will be smaller.

The most important thing is to look at its graduation value, for example, we can know that its graduation value is 1cm, which is an estimate.

2.If you don't write the unit 1dm, the minimum graduation value is the penultimate number (0 is also included), and the graduation value is 1dm

Mistakes are not errors Mistakes can be avoided But errors are inevitable According to the topic, the standard meter ruler is 1cm in length, and the actual meter ruler is 39cm, so the actual length of the desk is 39

b 2.There are no units; Because if there is an error in the measurement, it can be corrected, but the error cannot be avoided.

2.There is no writing unit 1cm3. Mistakes can be avoided, errors cannot.

1- A flask has just been removed from the flame, the water in the flask has stopped boiling, use a rubber stopper to plug the mouth of the flask, turn the flask upside down and pour cold water on the bottom of the bottle, the phenomenon seen is [re-boiling], the reason for this phenomenon is: [the temperature decreases, the air pressure in the bottle decreases, the boiling point decreases].

2- When a child has a fever, if there is only warm water, towels, hot water bottles, and quilts around, how can I cool down the child as soon as possible? Say with your method and reason: [towel dipped in warm water to wipe water vaporization and heat absorption].

3- When the rocket flies in the atmosphere, its head heats up, and the temperature can reach several thousand degrees Celsius. The head of the rocket is coated with a layer of special material, which melts and vaporizes at high temperatures, which can play a role in protecting the head of the rocket, because of [gasification and endothermy].

4- We call the average thermal motion of a molecule the temperature. Commonly used thermometers measure temperature using the principle of heat transfer (not necessarily right).

5- If you have an inaccurate thermometer, put it in a mixture of ice water and 3 degrees Celsius, put it in boiling water at a standard atmospheric pressure and 93 degrees Celsius, and put it in a classroom at 21 degrees Celsius, then the actual temperature in the classroom is [c].

A-20 degrees Celsius B-20 degrees Celsius degrees Celsius D - cannot be determined.

1. All solutions: generator power generation is to convert mechanical energy into electrical energy, electric furnace work is to convert electrical energy into internal energy, solar water heater to make water heat is to convert solar energy into internal energy, and motor power rotation is to convert electrical energy into mechanical energy

Therefore, choose b, I wish you progress, choose me.

Xiaohua collected some examples of energy conversion, among which the conversion of electrical energy into internal energy is: B electric furnace work.

From the point of view of energy conversion, after the electric fan is connected to the power supply and works normally, the result of the work done by the current is: d electrical energy is converted into internal energy and mechanical energy.

I hope it helps you, and if you have any questions, you can ask them

I wish you progress in your studies and go to the next level! (*

b. Electric furnace work.

Because of the conversion of electrical energy into internal energy.

dElectrical energy is converted into internal energy and mechanical energy.

Because the heat of the body is the internal energy, and the rotation is the mechanical energy.

You can follow up.

1.Pick B

A motor works to convert electrical energy into kinetic energy.

b Electric furnace works Electrical energy is converted into heat energy.

c. Thermal power generators generate electricity Chemical energy is converted into electrical energy.

d is the conversion of solar energy into thermal energy.

2.Pick D