Junior high school physics, thank you, detailed explanation, junior high school physics Please give

The power rating of the small bulb never changes, so it is wrong. The figure shows a parallel circuit, the voltage at both ends of the sliding rheostat is always equal to the power supply voltage, that is, U2 is unchanged, and the right resistance becomes larger, which is obtained by P=U2 R, when the voltage is constant, the greater the resistance, the smaller the electrical power, so B is wrong. The voltmeter shows that the voltage of the power supply is measured, and as long as the power supply does not change, its indication will not change, so C is wrong.

In the diagram, the ammeter A1 measures the current through the sliding rheostat, and A2 measures the total current, the difference of which is equal to the other branch, which is the circuit flowing through the small bulb. From i=u r, it can be seen that its current is related to the voltage at both ends of its resistance, and the resistance is a property of the conductor itself, so the resistance of the small bulb does not change, and the voltage of the parallel circuit is equal everywhere, so the voltage at both ends of the small bulb does not change, that is, the total current i does not change, that is, two electricity. The difference between the flow tables does not change, so d is correct. Hope.

The slip line rheostat is connected in parallel with the bulb, in the process of sliding the slide blade of the sliding rheostat from the midpoint to the right, the total resistance becomes larger, the total current decreases, the voltage at both ends of the parallel circuit is the power supply voltage according to the figure, which always remains unchanged, and the current flowing through the bulb remains unchanged. The current flowing through the bulb = A1-A2, so the difference between the A1A2 indicators of the ammeter remains the same. The answer is d

The rated power is an inherent attribute and will not change.

The resistor and the bulb are connected in parallel, the voltage is equal to the power supply voltage, v does not change, the power = u squared divided by r, r increases, so the power is small, b is not selected.

The voltmeter is connected in parallel with the power supply, and the voltage remains unchanged, and C is not selected.

The difference between A1A2 is always the current value of the bulb and will not change.

1) The phenomenon that will occur after the water boils is that the water vapor will flush the rubber plug out of this process, and the chemical energy of the fuel will be converted into internal energy, and the internal energy will be converted into mechanical energy through work.

2) Observe the experimental device and find that the test tube is filled with metal, and the function of this metal is to ensure personal safety.

Molecular gap: 10 ml of water + 10 ml of alcohol < 20 ml.

Molecular movement: A drop of ink is placed in a bottle of water, and it slowly spreads around until the bottle contains as much ink everywhere.

1.If the diagram and the question you provide are correct, then your answer must be wrong. From the figure, it can be clearly concluded that the luminous point must be outside the focal point (because the luminous point is the intersection point of AB), then the luminous point S must be on the other side outside the focal point to form a real image, (the real image is the intersection point of the refracted light), because S is not on the optical axis, so the image is not on the optical axis, (you can use the light through the optical center is still propagating along the straight line to determine), take a good look at the convex lens imaging law and the cause of the real image, you will understand.

2.You'd better do this experiment, I'm sure you'll be impressed. Because the paper tube will drive the surrounding air to move in the same direction as him, then the direction in which the air on the right side is driven (downward) is opposite to the direction of the air relative to the downward movement of the paper tube (upward), and the result of the offset is that the speed of the air relative to the paper tube becomes smaller (still upward), and the flow velocity is small and the pressure is strong, so it deviates to the left.

3.The magnitude of the buoyancy is equal to the weight of the discharged liquid, and at the beginning the displacement becomes larger (buoyancy increases), so the pressure needs to increase, and later the displacement remains the same (buoyancy does not change), so the pressure needs to remain the same. Buoyancy is the difference between the upper and lower surface pressure, pay attention to the upper and lower surface pressure is larger, but the difference remains the same, just like your income and expenditure have increased, you may not earn more money, in addition buoyancy is the resultant force of the upper and lower surface pressure, the buoyancy can no longer be considered when analyzing the force, just like if you calculate the workload of your class, if you calculate the total workload of your group, you can not add your workload. So you can see that the liquid pressure is not taken into account when analyzing this type of object (because the total amount is already taken into account, i.e. buoyancy).

4.If so, because ab is relatively stationary, it belongs to the category of static friction, static friction is the same as the power and the direction is opposite, and b can only have one friction in the horizontal direction, because the resultant force of uniform motion is zero, then the friction can only be zero (it is recommended to have a good understanding of static friction, which is different from b acceleration and deceleration) If this question pushes b, then the net force is zero, and the friction is equal to the thrust. The second void is to figure out what the sliding friction is related to, the surface roughness and the pressure, because the two are unchanged, so the friction is unchanged 12n (note that it has nothing to do with the force area).

5.I am afraid that you are influenced by the textbook's comparison with solids and liquids, because the spacing between gas molecules is very large relative to the molecular force, and the force is very small, which can be approximated as zero, and the gas molecules will move at a uniform speed without force, because there are more molecules, and collisions often occur, and the point is to ignore the molecular force.

1.Personally, I think the answer is a

Convex lens concentrating principle:

A convex lens is a lens that is thick in the middle and thin at the edges.

It has a converging effect on light.

The light rays parallel to the main optical axis are refracted by the convex lens and pass through the focal point on the other side.

The light rays that pass through the focus are refracted by the convex lens and parallel to the main optical axis.

Real image, virtual image:

The real image is made up of the actual light that can be imaged on the screen.

On the other hand, the virtual image is formed by the convergence of the extension line of the actual light in the opposite direction, and it is not impossible to image on the screen.

The imaging rules of convex lenses and their application (no need to memorize, just draw pictures according to the principle of concentrating).

Analysis: Let's start with the likelihood of the answer.

If you choose D, then you must choose B, and if there is no intersection on the other side of the convex lens, it is a virtual image, and the two answers are the same thing.

So b, d is definitely not right.

According to the diagram, it seems that U F, so although the answer A has the word 'certainly', it cannot be said that he is wrong.

C answers, since it is a point light source, unless the light source is on the main axis, otherwise the image will not be on the main axis, so C should be wrong.

2.Personally, I think it's 'moving to the left', and the deflection in the title is estimated to mean a slight shift.

But I didn't think much about air flow, and junior high school physics didn't seem to involve much aerodynamics.

Force analysis: tensile force of the line, gravity.

But the paper tube rotates clockwise, so the thread should be on the left side of the paper tube, so the pull of the thread should be slightly skewed to the left.

When the tension is decomposed, the left-facing component remains.

3.This question is very simple to choose D, as for your problem is a simple basic knowledge point, that is, to analyze the problem of the difference in the lower force between the upper and lower surfaces of the object.

Many reference books have explanations of this part.

f buoyancy = f lower surface - f upper surface.

So when it is completely intrusive, although the pressure or pressure changes, the difference does not change, so the buoyancy does not change.

12n first empty, due to uniform motion, ab as a whole, so tensile force = friction force = 12n = 2 mg

The second empty, because ab is exactly the same, ab is looked at separately, fa= mg, fb= mg, f=2 mg, so the thrust should be 12n

5.Air molecules should not collide with each other so easily, the gravitational force and repulsion between molecules are related to distance, when the distance is too close, the repulsion force is dominant, when the distance is too far, the gravitational force is dominant. As shown in the picture (this picture is not clear, it is better to refer to the picture in the book).

1 Analysis: Because the position of the point light source makes the object distance u may be greater than f or less than f, that is, it cannot be uniquely determined, so options (a) and (b) that must be a real image and a virtual image should be excluded. For option (c), it is conceivable that a ray of light from a point source to the center of the lens does not change the direction of propagation through the lens, and it is impossible for a refracted ray to intersect at a point in a real image or a reverse extension of a ray refracted in a virtual image to intersect at a point, so option (c) should also be excluded.

In option (d), if the point light source is positioned so that the object distance u f is formed, it becomes a virtual image, and the two rays of A and B do not intersect at one point after passing through the convex lens, but their reverse extension lines intersect on the left side of the lens, so option (D) is correct.

2 Left side. 3D pressure is equal to buoyancy.

When the ball is not completely submerged in the water, as it goes deeper, the buoyancy becomes more and more buoyant, and the pressure increases;

After being completely submerged in the water, the buoyancy remains the same and the pressure remains the same.

4 identical wooden blocks A and B are stacked on the horizontal tabletop, make a uniform linear motion, and are affected by the action of the equilibrium force, so the frictional force is equal to the tensile force, and the tensile force is horizontal to the right, then the friction force is horizontal to the left

Place A and B close to the horizontal tabletop for uniform linear motion Since the friction force has nothing to do with the movement speed and contact area, it is still subject to the thrust of 10N, and the friction is also 10N

So the answer: 10, horizontally to the left

5. The title has a picture.

The principle of convex lens imaging! It is divergent light.

(d) left, d, 10, horizontally to the left, because there is gravity between the ab points.

1 All the three gods upstairs choose c a b then should i choose d d- - the correct answer is b.

If water is injected into the right tube and the water level on the right rises, the air pressure in the air cavity on the left side of the U-shaped tube will increase, the air pressure in the small test tube will also increase, the volume of gas inside will decrease, and the water column in the test tube will rise. And because the weight of the test tube remains unchanged, it is necessary to maintain the balance of the test tube, and the buoyancy remains unchanged, that is, the height difference between the internal liquid level and the external liquid level remains unchanged. Based on the above two conclusions, the top of the test tube will drop relative to the external liquid level, so the small test tube will sink a little relative to the water surface in the left tube.

The explanation of the Rubik's Cube, if you don't understand, you can ask me no problem.

Q1: 8000 1000 Ox.

Second question: 8000-7000=1000

1000 1000 kg 1000 kg cubic meters = 1000 cubic meters.

The third question: It is calculated by f=ps.

It doesn't make sense to ask such questions.

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