How to determine the direction of the magnetic field of the current in the wire

Lenz's law is required.

to judge. It is elaborated as follows:

1. Lenz's law: induced current.

With such a direction, the magnetic field that induces the current always obstructs the magnetic flux that causes the induced current.

changes. Two.

Method steps for applying Lenz's law to determine the direction of the induced current:

1. Clarify the direction of the original magnetic flux passing through the loop, and whether it increases or decreases;

2. Determine the direction of the magnetic flux generated by the induced current in the loop according to the above meaning expressed in Lenz's law;

3. According to the law of the direction of the magnetic field generated by the loop current inside the loop (right-hand spiral law, the direction of the induced current is determined by the direction of the magnetic flux of the induced current.

3. The method of judging the direction of the current of the toroidal wire in the magnetic field by using Lenz's law.

1. Clarify the direction of the original magnetic flux through the toroidal wire, and whether it increases or decreases;

2. According to the principle of Lenz's law (always to hinder the change of the original magnetic flux), determine the direction of the magnetic flux generated by the induced current in the wire loop in the loop;

3. According to the direction of the magnetic field generated by the current of the wire ring inside the circuit, the right-hand spiral law is used to determine the direction of the induced current by the direction of the magnetic flux of the induced current.

With the right-handed spiral rule, the magnetic field formed by the current in the straight wire is circular, the right hand surrounds the wire, the thumb points in the direction of the current, and the direction of the four-finger finger is the direction of the magnetic field.

The rule of the right hand, the right hand holds the wire, the thumb points in the direction of the current, and the direction of the four fingers is the direction of the magnetic field.

The relationship between the direction of the current of the energized straight wire and the direction of the magnetic inductance line can be judged by the rule of the right hand straight wire (note the difference with the judgment of the energized solenoid), hold the straight wire with the right hand, the straight thumb is consistent with the direction of the current, and the direction pointed by the curved four fingers is the direction around the magnetic inductance line.

The medium is in a non-uniform magnetized state, that is to say, usually the magnetic field lines inside the medium are in a curvilinear state and unevenly distributed; In addition, since there are electric insulators in nature, there are no magnetic insulators (except for superconductor substances), so there is magnetic flux leakage in the usual magnetic circuits.

By using magnetic wires, the direction of the magnetic field in energized wires can be determined. When a magnetic wire is placed in a wire, it vibrates or moves in a certain direction, and the direction of the magnetic field in the energized wire can be judged based on the direction of vibration or movement of the magnetic wire.

In electromagnetic induction, the direction of the current is judged by the right-hand rule: stretch out the right hand, make the thumb and the other four fingers at right angles, and put the right hand into the magnetic field, like a magnetic inductance line.

Vertically into the palm of the hand (when the magnetic inductance line is a straight line, it is equivalent to the palm facing the n pole), the thumb represents the direction of the wire movement, and the direction of the four fingers is the direction of the induced current in the wire.

The right-hand rule is a very important law in electromagnetic induction, and it is often confused with the left-handed rule. The right-hand rule is mainly used to determine the direction of the induced current, which is independent of the force, and the left-hand rule is mainly used to judge the direction of the force movement through the current wire in the magnetic field. It can be simply understood as using the left hand for electricity and using the right hand for moving electricity, for example:

1. Electromagnetism.

- The rule of the left hand of the motor ---: the palm of the hand faces the magnetic field line.

Four fingers are the direction of the current, and the thumb is the direction of the electrodynamic force.

2. Magnetism generates electricity.

- The right-hand rule of generator ---: the palm of the hand faces the magnetic field lines, the thumb is the direction of movement, and the four fingers are the direction of the induced electric potential.

The dots and forks both indicate the direction of the source of the jujube, the dots indicate that the vertical paper faces outward, and the fork indicates that the vertical paper faces inward.

In physics, dots and forks are drawn in a way that generates a magnetic field around an electric current in a vertical direction: the vertical paper is crossed in the inner circle, and the dots are drawn in the outer circle.

Determine the direction of the current: Extend your right hand so that your thumb and four fingers are perpendicular to each other and on the same plane; Place your right hand in the magnetic field so that the magnetic lines pass vertically through the center. The direction your thumb points in the direction of the conductor's movement, and the direction in which the other four fingers point is the direction in which the current is induced.

If you let the currents flow in the same direction, they will attract each other; At opposite currents, they repel each other.

1. Point out the fork in: the fork into the magnetic inductance line from near and far, as if the arrow is seen to be the tail of the arrow, and the point out is the magnetic inductance line from far and near, as if the arrow is shot, the arrow is seen, and the chiral rule is two

1. Both the electromagnetic and magnetic generators are right-handed, and the direction of force is judged to be left-handed;

2. The four fingers always point to the current;

Second, the fork in and out of the judgment direction:

1. Electromagnetism: Judge the vertical broken magnetic pole, hold the solenoid with the right hand, and the four fingers are consistent with the direction of the current, then the thumb is the direction of the n pole.

2. Magnetic electricity: judge the direction of the induced current, stretch out the right hand, let the magnetic inductance line pass through the palm, and the thumb points to the direction of cutting the magnetic inductance line, then the direction of the four fingers is the direction of the induced current.

In the direction of the force of the energized conductor in the magnetic field, stretch out the left hand, let the magnetic inductance line pass through the palm, and the four fingers point to the direction of the current, then the direction pointed by the thumb is the direction of the force movement.

Right-handed spiral rule: Determine the relationship between the direction of the magnetic inductance line and the direction of the current.

As shown in the figure, if you hold the energized coil (solenoid) with your right hand so that the bent four fingers are in line with the direction of the current in the coil, then the direction pointed by the thumb is the end (n pole) of the magnetic inductance line in the coil. As long as one of the directions (current direction or magnetic inductance line direction) is known, the other direction can be determined.

The direction of the magnetic inductance line inside the energized solenoid is from the S pole to the N pole; The direction of the magnetic inductance line on the outside is from the n pole back to the s pole.

Note: The direction of the bending of the four fingers should be consistent with the direction of the current in the coil (one turn at a time), and do not just look at the straight parts at both ends to avoid mistakes.

To solve this problem, you need to first figure out that you are passing an electric current through a coil to judge the magnetic field generated; Again, the coil moves in a magnetic field to determine the direction in which the induced current is generated. In the former, the right hand spiral rule of annular current is used, so that the four fingers of the right hand are bent in the same direction as the coil annular current, and the direction pointed by the straight thumb is the direction of the magnetic inductance line on the central axis of the coil; The latter, judging by the rule of the right hand, stretches out the right hand, so that the thumb and the other four fingers are perpendicular to each other, and in the same plane with the palm of the hand (that is, all the fingers are extended), so that the magnetic inductance line passes perpendicular to the palm, the thumb points to the direction of the coil frame movement, and the direction of the other four fingers is the direction of the induced current.

The method of judging the direction of the magnetic field of the linear current is as follows:

The direction of the magnetic field of the energized straight wire can be used"The left-handed rule"to be sure. "The left-handed rule"This means that the palm of the left hand is pointed in the direction of the current, and the thumb of the left hand is pointed in the direction of the magnetic field.

Specifically, assuming that the current flows from left to right, you can use the four fingers of your left hand to point in the direction of the current and your thumb to point in the direction of the magnetic field. If the current is flowing from right to left, you can point the thumb of your left hand in the direction of the current and your four fingers in the direction of the magnetic field.

Note:"The left-handed rule"It is only applicable to the determination of the magnetic field direction of a straight wire, and for the determination of the magnetic field direction in other cases, other methods may be required.

After Oster discovered the magnetic effect of electric current through the famous "Oster experiment", the French physicist Ampère further did a lot of experiments to study the relationship between the direction of the magnetic field and the direction of the current, and summarized Ampère's law, also known as the right-handed spiral rule.

In the case of direct current, the direction of the current needs to be known, the thumb of the right hand is vertically extended, the direction of the thumb is the direction of the current, and the direction of the four fingers is the direction of the magnetic field. The direction of the magnetic field at the AC point is constantly changing with the direction of the current.

In the case of direct current, if the direction of the current is unknown, the wire can be wound into turns, spring-shaped, such as evenly wrapped on a pencil, and the hoop wire is like a magnet, and the direction of the magnetic field can be directly known through the bar magnet, and then the direction of the current can be obtained. Ampere's rule, also known as the right-hand spiral rule, is a rule that expresses the relationship between the direction of the magnetic inductance line of the electric current and the magnetic field excited by the current.

The direction of the magnetic field of an energized wire can be judged by the left-handed rule.

If you put a straight wire on electricity, then put it in a uniform magnetic field, and the conductor will be moved by the action of the electromagnetic force f. The direction of the current will not change, what needs to be judged is the direction of movement of the conductor under the action of electromagnetic force, and the relationship between the direction of the current, the direction of the magnetic field, and the direction of the electromagnetic force can be judged by the left-handed rule.

Stretch out the left hand, the thumb is perpendicular to the other four fingers, the magnetic field lines pass through the palm of the hand (that is, the palm of the hand faces the n pole), the direction of the four fingers is the direction of the current, and the direction of the thumb is the direction of the force of the energized conductor (that is, the direction of the electromagnetic force f).

Judgment of the direction of the magnetic field of the unenergized wire:

If the straight wire is not electrified, then put it into a uniform magnetic field to cut the magnetic field line. Then an induced electromotive force (according to the law of electromagnetic induction) is generated in the conductor, and the relationship between the direction of the current, the direction of the conductor's motion, and the direction of the magnetic field can be used by the right-hand rule.

Stretch out the right hand, the thumb is perpendicular to the other four fingers, the magnetic field lines pass through the palm of the hand (that is, the palm of the hand faces the n pole), the direction of the thumb is the direction of the movement of the conductor, then the direction of the four fingers is the direction of inducing electromotive force (that is, the direction of inducing current). <