What is Magnetomotive Force?
Magnetomotive force (or magnetomotive force) is a physical quantity in a magnetic circuit, which is equivalent to the electromotive force in a circuit. Refers to a measure of the magnetic effect of current in a coil. Measured in ampere turns and depends on the number of coil turns.
- The magnetic field strength is integrated along the line of the closed path, which is also called magnetomotive force. In many electrical installations, the magnetic flux is generated by the current in the coil. According to the Ampere Loop Theorem, the line integral of the magnetic field strength along the closed path is equal to the product NI of the current I and the number of coil turns N in the coil surrounding the path. Therefore, in electrical engineering, the magnetomotive force along a closed path is defined by the product NI. The direction of the magnetomotive force on the closed path and the direction of the current in the coil should conform to the right-handed spiral rule. If there are more than one coil, the magnetomotive force is equal to the algebraic sum of the NI of each coil. In the International System of Units (SI), the unit of magnetomotive force is Ampere (A). Engineering also uses ampere turns as a unit of magnetomotive force.
- The law of the relationship between magnetoresistance, magnetomotive force, and magnetic flux. It includes the first law of magnetic circuits and the second law of magnetic circuits.
- The first law of magnetic circuit The algebraic sum of magnetic fluxes passing through any node in the magnetic circuit is zero. The magnetic circuit in Fig. 2 has two branch points a and b. The branch point of the magnetic circuit is usually called a node, the magnetic flux entering the node is positive, and the magnetic flux leaving the node is negative. A closed surface S is made at the node a, and 1 + 2 - 3 = 0 is obtained according to the principle of continuity of magnetic flux, which expresses the relationship between the magnetic fluxes of the branches at the magnetic circuit node. This law is determined by the nature of the magnetic induction line. The magnetic induction line is a closed curve without a head and no tail. Therefore, the first law of the magnetic circuit is also called the law of continuous flux, and it is also called the Kirchhoff first law. It clarifies that the magnetic flux in the magnetic circuit is conserved and plays an important role in the calculation of the magnetic circuit.
- figure 2
- The second law of magnetic circuits. For any circuit in a magnetic circuit, the algebraic sum of its magnetic potential is equal to the algebraic sum of its magnetic potential drops. In the figure, the closed loop composed of l 1 and l 3. If we take their center line as a closed loop and circle clockwise, applying the law of full current, we have N 1 I 1 = H 1 l 1 + H3 l 3 . Then take the closed magnetic circuit composed of l 1 and l 2 and still go clockwise along the center line of the magnetic circuit. Applying the law of full current, there are N 1 I 1 -N 2 I 2 = H 1l1 -H 2 l 2 . For closed loops, the second law of magnetic circuits is essentially the law of full current, and for a certain section of the magnetic circuit, it is the Ohm's law of magnetic circuits, and the second law of magnetic circuits, also known as Kirchhoff's second law. It is an important basis for magnetic circuit calculation. When the second law of the magnetic circuit is applied, the determination method of each magnetic potential and magnetic potential drop direction is: arbitrarily select the looping direction of the loop. When the magnetic flux direction and the winding direction are the same, the magnetic potential drop of the segment is positive, otherwise it is negative; when the direction of the current in the coil and the winding direction conform to the right-hand spiral rule, the magnetic potential of the coil is positive, otherwise it is negative.
- The second law of magnetic circuits plays an important role in the calculation of magnetic circuits. [2]