A question for junior high school physics experiments! Urgent, junior high school physics experiment

There's a lot of air in a down jacket, and it's warm to wear on the body; The water in a thermos that is filled with boiling water is slower than when it is not filled with boiling water, and the water in the thermos that is not filled with boiling water cools slowly; All of this shows that air is a poor conductor of heat.

Let's do a comparative experiment by using an empty box, a box filled with plastic, and a box filled with water, and heating each other, and measuring the temperature change on the non-heated surface.

The water in a thermos that is filled with boiling water is slower than when it is not filled with boiling water, and the water in the thermos that is not filled with boiling water cools slowly;

The one on the first floor is not right, is this the case in life? It seems that the cooling of the water is slower.

The second floor is good and feasible.

I'll also give you a simple example, think about it, when boiling water, turn on the stove, but don't put the kettle on the stove, just close to the stove, so that the water will not open, because the air is a bad conductor of heat, and the heat of the furnace fire cannot be transferred to the water through the air, but if the kettle is placed on the stove, the water can be boiled, this is because there is only one medium between the water and the stove - the kettle, the material is generally aluminum or stainless steel, which is a good conductor of heat.

It's very simple

1.Fill 2 identical bottles with water at the same temperature.

Put the bottle in tap water and the other bottle in the air.

3. Measure the temperature of 2 bottles of water after a period of time.

Protocol Procedure:

1) Inject an appropriate amount of water into the graduated cylinder and read out the volume of water v0 at this time; Tie an aluminum block with a thin wire to immerse it in the water in the graduated cylinder, and the corresponding scale value of the water surface in the graduated cylinder is represented by V; The data of v0 and v are recorded in the experimental data record table.

2) Fill the beaker with an appropriate amount of water, measure the total mass of the beaker and water m0 with an adjusted balance, and write it down.

in the experimental data record sheet; The aluminum block in step (1) tied with a thin wire is suspended and submerged on the left disc of the balance.

In the water inside the beaker, the aluminum block does not touch the beaker, add an appropriate amount of weight to the right plate of the balance, move the yard, and the balance.

When re-equilibrizing, the sum of the total mass of the weights in the right side of the balance and the scale value of the yard is expressed by m, which is m.

The data are recorded in the experimental data record sheet.

3) Replace the aluminum blocks with different volumes, imitate the steps (1) and (2) and do 5 more experiments, and read out the data of the scale value v corresponding to the water surface when they are immersed in the water of the graduated cylinder; The corresponding data of m when each aluminum block is suspended and submerged in the water of the beaker were measured separately; The data of V and M for each time were recorded in the experimental data record sheet.

4) According to V row V v0 and F float mg m0g, the data of V row and F float for 6 times were calculated and recorded in the experimental data record table. Experimental Data Logging Table.

v0/m3v/m3

V-row M3M0 kg

m kgf float n

Analysis: There is a problem with the solution upstairs, if you already know the formula f float = m row g, there is no need to do this test, the volume of the object immersed in water is equal to the volume of the object, the difficulty of this experiment is how to measure the amount of buoyancy of the object in the water. The experimental conclusions are then drawn based on the relationship between the measured buoyancy and the volume.

Steps: 1 Pour an appropriate amount of water into the graduated cylinder (it can submerge the aluminum block without overflowing), and record the volume L1 at this time

2 Place the graduated cylinder on the balance and measure the total volume of the graduated cylinder m1

3. Tie the aluminum block with a thin wire and slowly put it into the graduated cylinder until it is submerged, and measure the water volume L2 and the total mass m2 at this time (pay attention not to let the aluminum block touch the cylinder wall and the bottom of the barrel during the measurement).

4 According to the magnitude of the buoyancy of the object = m2-m1 The volume of water discharged by the object = l2-l1 ; Record the experimental data, and repeat the above steps with different aluminum blocks.

5. Drawing, the abscissa is the buoyancy size, the ordinate is the volume size, and the experimental conclusion is drawn according to the experimental data.

It may be difficult to understand the fourth step, the increase in the total mass m2-m1 after submerging the aluminum block in water is the buoyancy force of the water on the aluminum block, and the force action is mutual. I hope you understand well. ）

Solution: There are two problems that need to be solved in this experiment: one is the volume v row of water discharged by the object; The second is to measure the magnitude of the buoyancy f float.

Problem one is relatively easy, drainage method.

Question 2 is a bit troublesome. I feel that I can fill a beaker with an appropriate amount of water and weigh its total mass m1 with a balance; Then, after tying the weight with a thin wire, submerge it in water, and then weigh the total mass m2 at this timeThis way you can know the amount of buoyancy. Specific:

M row = m2-m1

f float = m row g

Therefore, the formula for calculating the amount of buoyancy in each step of this experiment is: f float = (m2-m1)g After figuring out the principle, I believe you can solve the remaining problems. Good luck!

1 Inject an appropriate amount of water into the graduated cylinder Read out the volume of water v0 at this time and record it in the table Inject an appropriate amount of water into the beaker Measure the total mass of the beaker and water with an adjusted balance m and record it in the experimental data record table (2) Tie an aluminum block with a thin wire to immerse it in the water in the graduated cylinder At this time, the scale value corresponding to the water surface in the graduated cylinder is v total 1 Hang an aluminum block tied with a thin wire and immerse it in the water in the beaker on the left disk of the balance The aluminum block does not touch the beaker Add an appropriate amount of weight to the right disk of the balance Move the play code When the balance is balanced again, the total mass of the weight in the right disk of the balance and the scale value of the symbol m total 1, and the total v 1, m1 and m total 1 are recorded in the table. 3 Switch to different volumes of aluminum blocks, imitate step 2, do 5 more experiments, read them out in turn, when they are immersed in the water of the graduated cylinder, the corresponding scale value v total 2---v total 6 of the corresponding aluminum block is measured, and the total mass of the weight in the right plate of the balance and the scale value of the game code are 2---m total 6 when the corresponding aluminum block is suspended and immersed in the water of the beaker, and the total amount of m 6 is recorded in the experimental data record table. 4) According to V row V v0 and F float mg m0g, the data of V row and F float for 6 times were calculated and recorded in the experimental data record table.

Experimental Data Log Table v0 m3

v total m3v row m3

m kgm total kg

ffloat n

3. The distance at which all the blocks are moved in the horizontal plane.

The magnitude of the kinetic energy of the velocity object is related to the mass.

Two steel balls with equal volume and mass are selected, the two steel balls are placed at different heights h1 h2, and the two balls are rolled down from the height of h1 h2 in the same inclined plane respectively in the experiment, and hit on the same wooden block placed on the horizontal plane, and the distance of the wooden block moving in the horizontal plane is observed.

(1) The distance that the two balls push the wooden block to slide over.

2) Height. 3) Release two balls at the same height, and the kinetic energy of the copper ball is greater than the kinetic energy of the steel ball (4) Use the same small ball (copper ball or steel ball) to release from different heights, and observe the distance that the ball pushes the wooden block to slide.

(1) How far the block will knock out.

2) Speed. 3) The magnitude of the kinetic energy of an object is related to its mass.

4) Roll down with copper or steel balls at different heights.

1.The distance at which the wooden block rolls is 2Height 3The magnitude of kinetic energy is related to mass4Roll down with steel balls of the same mass from different heights to see the distance traveled by the wooden blocks.

Voltammetry resistance measurement experiment.

1 A student uses the equipment shown in Figure 1 to measure the resistance of a small bulb by "voltammetry".

Figure 11) Please mark the meter type in the circle of the circuit diagram, and use the stroke line instead of the wire to connect the actual diagram

2) Before the switch is closed, the rheostat should be sliding.

The slider is moved to the end

3) If the switch light is not on, but the voltage is indicated.

The number is approximately equal to the supply voltage, at which point the fault occurs.

It could be . 4) If the voltmeter or ammeter is damaged during the experiment, the maximum resistance of the sliding rheostat is known to be r0, and only one of the two meters is allowed, Figure 2

Can you measure the resistance of a light bulb without adding other equipment? Please draw the circuit diagram in the dotted box in Figure 2, write a brief experimental procedure, and write the final expression of the physical quantities to be measured and RL

Experimental procedures and measured physical quantities:

rl

2. Give you a resistor r0 with a known resistance, a voltmeter, a switch, a battery pack and some wires, and please use these devices to measure the resistance of the unknown resistance rx. Requirements: (1) Draw a circuit diagram; (2) write out the main steps of the measurement; (3) Write an expression that calculates rx.

3. Give you a resistor r0 with a known resistance, an ammeter, a switch, a battery pack and some wires, and use these devices to measure the resistance of the unknown resistance rx. Requirements: (1) Draw a circuit diagram; (2) write out the main steps of the measurement; (3) Write an expression that calculates rx.

Content from user: Li Zi.

Classification and review of junior high school physics experiments.

Part I: Theoretical Basis.

1. Theory of measurement.

a) Measure the essence.

Measurement is a comparison. In order to make a scientific comparison, there needs to be a recognized standard quantity as the basis for comparison, and this standard quantity is called

In order to facilitate communication, a set of internationally accepted unit systems - the "International System of Units", abbreviated as "SI". Please fill in the principal units of each of the following quantities in the International System of Units:

Mechanics, electricity, thermothermal fluctuations, and acoustic function and energy

Length, Current, Temperature, Frequency, Function, Energy, Time, Voltage, Period, Power, Quality, Resistance, Amplitude, Density, Wavelength, Speed, Loudness, Force, Pressure

2) Error theory.

1. Errors and errors.

The difference between the measured value and the true value is called the error. Any measurement will have errors, which can not be absolutely avoided; And mistakes can and should be avoided.

2. Factors influencing error.

1) Measuring tools. The more precise the tools used for the measurement, the deeper the error becomes

2) The method of measurement.

3) Estimation. Measurements always have to be estimated, so measurements always have to produce errors.

3. Methods to reduce errors.

1) The error can be reduced by using more precise measurement tools and designing more scientific measurement methods.

2) Multiple measurements, taking is an important way to reduce the error.

Note: 1) "Multiple measurements", usually three times;

2) When taking an average, the digits of the average value must be the same as the digits of the measured value.

2. Science**.

Science** generally goes through the following seven steps: Due to the divergent nature of "conjectures and hypotheses", it is less likely to occur in exams. We emphasize that "conjectures and hypotheses" must be made reasonably on the basis of the situation of the test questions, and arbitrary conjectures are opposed. 4 Second.

The habit of expression can be seen by looking at the language of the subject's question, and the first sentence of this question "to study the characteristics of the use of sliding" is.

The conclusion of the question is very simple, the first item is to use a pulley or not, and it will save effort if it is used. The second item is that the lighter the movable pulley, the smaller the spring dynamometer. However, you will not be able to get a full score for answering the question in this way.

The correct scriptor should be:

1) Lifting heavy objects of the same mass, using movable pulleys can save effort.

2) Use movable pulleys with different gravity to lift heavy objects of the same mass, the lighter the gravity of the movable pulley, the more labor-saving.

Summary: Speak rigorously, that is, put the premise of various situations in front first, such as "lifting a heavy object of the same mass", "using movable pulleys of different gravity to lift a heavy object of the same mass"; Then translate the experimental phenomenon into the language habit of the questioner, not to say that the number is small, but to say that the movable pulley is lighter and more labor-saving.

1. The movable pulley can save labor, but it cannot change the direction of force.

2. The smaller the mass of the pulley itself, the higher the mechanical efficiency of the pulley.

1. Using movable pulleys to lift heavy objects can save effort, but it cannot change the direction of force.

2. Use the movable pulley to lift the same weight at a constant speed, the greater (small) the gravity of the pulley, the greater (small) the pulling force used

Question 1: The easiest way is to use it to look at distant objects, if the object is upright, the lens is a concave lens, and if the object is upside, the lens is a convex lens. The reason is that the concave lens assembly is inverted to reduce the virtual image, while the convex lens is inverted when the object distance is greater than 2 times the focal length. So if you see an upside-down object, then the lens you use must be a convex lens.

Question 2: If you imagine a car that starts and returns at the end of the car, then its speed is equal to the distance divided by the time. The distance is twice the distance between you and the building, and the speed is naturally 2s divided by the time.

Holding the lens facing the sunlight, adjust the distance from the lens to the ground to see whether the spot on the ground is larger or smaller than the lens, if the lens is large, the lens is a concave lens (divergence), if the spot is smaller than the lens, this lens is a convex lens (converging lens).

Problem 1, 1, the circuit diagram is shown in the figure above;

2. Experimental Procedure:

a, according to the designed circuit diagram to connect the circuit;

B. Close the switch S, properly adjust the sliding rheostat, and measure the voltage (UX and UO) at both ends of the fixed resistance Rx and RO with a voltmeter;

3. The resistance value of the measured resistor is: rx=uxro uo

Question 2, 1, the circuit diagram is shown in the following figure;

2. Experimental Procedure:

a, according to the designed circuit diagram to connect the circuit;

b, Closed switches, the current in the sliding rheostat maximum and minimum measurement circuit (i'With i'')；

3. The resistance value of the measured resistor is: rx=i'r'/(i''-i'Note that the power supply voltage remains the same [ i'(rx+r')=i''rx 】