A B is two identical steel rods, with one end of A near the middle of B, the following statement is

Option d is correct.

Cause analysis: Accurately determine which steel rod has magnetic content: two steel rods with the same shape, one is magnetic, the other is not, if there is no other utensils, how can we know which one is magnetic and which is not?

Students will come up with two methods, but neither of these methods can accurately judge whether the steel rod is magnetic or not, please see the following analysis: Method 1: Place a steel rod on a horizontal plane and use another steel rod to approach it, if the steel rod on the table is attracted, then the steel rod is not magnetic; If the on the desktop is not attracted, then the is magnetic.

Analysis: When a magnetic steel rod is close to a non-magnetic steel bar, the non-magnetic steel bar will be magnetized, and the end of the magnetic pole near the magnetic pole of the magnetic steel rod will appear with a different name, so the two steel rods are always attracted to each other, which shows that this practice is incorrect. Method 2:

Hang the two steel bars separately so that they are stationary horizontally, the one pointing north and south is magnetic and the other is not. Analysis: Non-magnetic steel rods are suspended, and they may also guide north when stationary, and if both steel rods are guide north, it will not be able to judge, so this practice is also incorrect.

Therefore, in order to draw conclusions through experiments, it is necessary to clarify the following questions:

1. The properties of objects such as iron, cobalt, nickel, etc., are called magnetism; Clause.

Second, the part with the strongest magnetism is called the magnetic pole, and the magnet has the strongest magnetism at both ends and the weakest magnetism in the middle; Judging method: take a steel rod in your hand to touch the middle part of another steel bar, if you find the attraction phenomenon, the steel rod in your hand is magnetic, if the attraction phenomenon does not occur, then the steel rod in your hand is non-magnetic, that is, the magnetic is another steel bar.

The middle part of the D magnet is not magnetic, so it can be judged that B must be magnetic, but A is not sure.

1) The most magnetic part of the magnet is called the magnetic pole, which is located at the two return ends of the magnet, and the weakest part of the magnet is in the middle of the magnet, which is almost not magnetic

2) When one end of B is close to the middle part of A, B is sucked up by the leakage source, so it can be determined that the iron rod B has the magnetism of Huai bucket, but it cannot be determined whether A is magnetic or not; If A is magnetic, when one end of A, the most magnetic part, is used to approach the middle part of B, B should be attracted, but in fact there is no attraction, indicating that the iron rod A is not magnetic

Therefore, choose D

The most magnetic part of the magnet is called the pole, which is located at both ends of the magnet, and the weakest part of the magnet is in the middle of the magnet, which is almost not magnetic

When one end of the B rod touches the middle part of the A bar, it attracts each other, so it can be determined that the steel rod B is magnetic, but it cannot be determined whether the steel bar A is magnetic or not

Therefore, choose D

dRegardless of whether B is magnetic or not, it does not exhibit magnetism in the middle. Therefore, if they are not attracted to each other, it is not certain whether B is magnetic or not, that is, it may be magnetic, and of course it may not be magnetic. However, it can be determined that the nail must be non-magnetic, and if the nail is magnetic, it will definitely attract each other.

c If they are not attracted to each other, then A and B are non-magnetic.

Answer: The basic property of a magnet is the effect of the magnetic field force generated by the magnet placed in its magnetic field When one end of A is close to one end of B, B rotates, indicating that the effect of the magnetic field force between A and B If the magnetic field force is gravitational force, one of A and B must be magnetic, or both of them are magnetic If the magnetic field force is repulsion, then A and B must be magnetic The known conditions given in the question do not determine whether the rotation is due to attraction or repulsion Therefore, d is correct

B is correct, there is no magnetic force at the magnet break, there is a magnetic force at both ends, so it is not possible to judge whether B has magnetism, if A can absorb B, it can only mean that A has magnetism!

Because the magnetism in the middle of the magnet is very weak, it should be selected as A is magnetic, B is unknown, and CD can not judge whether B is magnetic or not.

Because the magnetic poles of different names can attract each other, and the magnet can also attract magnetic materials without magnetism, so the steel rod with the same shape, when one end of B is close to one end of A, A is attracted and rotates, which can only indicate that one of them must be magnetic, the other may be magnetic, or it may be a magnetic material without magnetism

Therefore, choose D

C One end of the B rod can absorb the middle of the nail stick, then it is said that Ling is as good as a sock, Bu Ming B must be magnetic, if the title is changed to one end of the B rod can absorb the end of the nail stick, the result is still the same, but at this time, if A is magnetic, it must be the opposite of B.