A physical choice, online, etc. Physics two choices, please tell me why

C: Resistance is a property of the substance itself, it cannot be said that it is proportional to what, r=u i uses the ratio definition method, so choose c

It doesn't matter if the circuit is disconnected or not.

First of all, there is no Ohm's law to talk about in the broken circuit, that is, Ohm's law does not hold in the open circuit, and C says that resistance is a property of the conductor itself, and the magnitude is equal to the ratio of voltage to current. This is wrong, resistance, because of the hindering effect of the substance on the electric current, so it is called the resistive substance under its action. In physics, resistance is used to express the magnitude of a conductor's resistance to an electric current.

The greater the resistance of a conductor, the greater the resistance of the conductor to the current. The resistance of different conductors is generally different, and resistance is a characteristic of the conductor itself. A resistive element is an energy-dissipating element that hinders the current current.

d I remember that in the third year of junior high school, the teacher said that the current in the conductor is proportional to the voltage at both ends of the conductor, and inversely proportional to the resistance value of the conductor. That's the CD difference.

.Remember to choose the answer you want

It should be selected that the voltage is not certain in the DA.

B does not say that the voltage is certain.

In c, resistance is a property of a conductor and is independent of current and voltage.

Knowing the u i at a certain moment in time can deduce the size of r, but the ab option means that r changes with i u, which is not true, and u changes so that i changes instead of r with it.

r=u i, which is the definition of resistance, not the determinant of resistance, so c is true and d, and the definition is r= l s l is the length and s is the cross-sectional area.

c The first sentence said is correct. But the second sentence is wrong. It is said that it is a property, how can it be equal to the ratio of current and voltage.

d Since a, b, c are all wrong. I had to choose D.

Positive solution: The resistance of a conductor is a property of the conductor itself. It has nothing to do with the current and voltage.

<> answer from the Internet to tell Sun for reference.

Click to view the Great Void Zen diagram.

Shake the dice. How simple.

Choose A, the first floor is made by yourself, good.

ABA (OK) BCD is uncertain (it is not known whether the state of the ball is sinking to the bottom or floating and levitating).

a Certainly not;

b The problem of the heating part is not stated in the burning of the stove, and the heating part does not necessarily have to be metal;

c Because I don't know if it's a high school or junior high school question Whether the concept of permanent magnets is being tested, since it is a 50% power saving, then it means that the magnetism of the section of the argument does not need current to maintain its magnetic field or does not use so much electricity! So I think it should be C

d Not covered in this question.

This problem is simple, remove one force, and the resultant force of the other two forces is equal to the magnitude of the removed force in the opposite direction.

Because the direction of force and the direction of motion are not necessarily related, so

The object should move in the opposite direction of the same acceleration as f, note that the acceleration mentioned here is a vector concept, that is, only the acceleration is fixed, according to the angle between acceleration and velocity, the object may move in a straight line or a curve, and d should be selected

If one force is abruptly withdrawn, the resultant force of the other two forces is equal to the force removed, in opposite directions, and the correct option can be selected based on this.

Possible. Velocity is a vector, so it's going to be discussed by category here.

1. When the velocity at the beginning and end is in the same direction: the velocity at the midpoint of time is 7 meters per second, the displacement is 7 meters, and the acceleration is 6 meters per square second;

2. The initial and final velocity is reversed, and the initial velocity is positive, then a = -14m s, and the displacement x = 4 + m at this time the acceleration is 14 meters per quadratic second, greater than 10 meters per quadratic second.

The question gives the velocity magnitude, so the possible change in velocity is 14m s

So the answer D is right.

A and D are both correct.

Acceleration is an acceleration motion or it may be a deceleration motion.

The acceleration is 6m s2When slowed down, it's 14m s2

There are two cases: the direction of the velocity does not change and the velocity has reversed after 1s.

Choose A, D

d can be a velocity equal to 4m s in the negative direction, and 10m s in the positive direction after 1s, so the change in v is 14m s in 14m, so a=14m s 2 > 10m s

a That's right.

dCarpets generally do not conduct electricity, so it will generate static electricity, which will cause some small objects to "suck" on it, weaving into the wire can enhance the conductivity of the carpet and make it easier to clean.

Why do you want to post pictures in reverse?

The question is an order of magnitude too heart-wrenching.

First of all, ideally, neither AP nor BP connection has any effect on circuit A-R1-R2-B.

It is easy to know that the voltage at both ends of the capacitor is the voltage at both ends of R1 when the AP connection method is used (there is no current at R3 in the open circuit, and it is said that the idealization consideration, so R3 does not divide the voltage), and the same is the BP connection method, because when R1 is connected to AP, P is directly connected to the right plate and point A of the capacitor, so the potential of the right plate is 3V, and the left plate is connected to the end of R1 (. . . 3V is stepped-down by R1, so the potential of the left plate is lower than that of the right plate, so the left negative and the right positive (it is recommended that you consider the movement of the charge in the lower circuit, so that why the left plate is negatively charged and the right plate is positively charged, and you can learn natural science well by thinking diligently), and the current direction is B to A first

It's a changeover! bp, the same as the above, at this time the left plate potential is higher than the right plate potential, left positive right negative, and before it was left negative right positive, so the circuit current is a to b, so the current direction first... So a right.

The amount of charge passing through R3 flows through it in two parts.

First of all, the voltages at R1 and R2 can be obtained, respectively.

For the first time, when ap, the amount of charge of the plates is orders of magnitude.

The second time, BP, the final charge of the plate is... However, there is a problem to be noted, at this time, the electrical properties of the plate have changed compared to the first time, so the amount of charge flowing through R3 for the second time is . +

So the total amount of charge flowing is . *2+。。Finished.

The mass of the three objects is equal, the density of lead is the largest, so the volume is the smallest, and when submerged in water, the volume of the water discharged is the smallest, and the liquid level rises the least.

All and so on to choose C

c The volume of water is equal, the density of lead is the largest, and the volume is the smallest under the condition of the same mass.

The cup where the lead is placed has the lowest water surface. When the mass is the same, lead has the highest density and the smallest volume, and when placed in water, the least amount of water is discharged. then the water surface is the lowest.