stayelectromagnetic inductionPhenomenon caused by the change of magnetic flux of conductor cutting magnetic induction line or closing coilemfIt is called induced electromotive force.
From 1825 to 1826, Georg Ohm did a lot aboutCircuitExperiment.In 1827, he published Mathematical Research on DC Circuit（Die galvanische Kette, mathematisch bearbeitet）These experiments and the results obtained from them, including the famous“Ohm's law”。Ohm noticed that the power required by the circuit is supplied by the battery, and the battery should be closely related to various physical phenomena in the circuit.He reasoned that the battery had a "driving force" that could drive current through the circuit.He willVoltaic batteryWhen connected in series, it is found that the current is proportional to the number of voltaic batteries.Therefore, he proposed that the driving force is proportional to the current.The driving force is the electromotive force. In a simple resistance circuit, the electromotive force is equal toelectric currentmultiplyresistance。
In 1831,Michael Faraday He did a series of experiments on electromagnetic induction. From these experiments, he found the following points:
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When the current of the current carrying wire is changed, the nearby closed circuit will be induced with current.
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When movingmagnetThe nearby closed circuit will be induced with current.
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When the closed circuit is moved near the current carrying wire or magnet, the closed circuit will be induced with current.
In 1832, Faraday found that the induced current produced by different wiresconductivityIs proportional.Since the conductivity is inversely proportional to the resistance, it shows that the induction involves the electromotive force, and the induced current is formed by the electromotive force driving the charge of the wire to move;Moreover, whether the wire is an open circuit or a closed circuit, it will induce EMF.
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(1) No matter whether the circuit is closed or not, as long as the magnetic flux passing through the circuit changes, the induced electromotive force will be generated in the circuitElectromagnetic induction phenomenonThe essence of.
(2) Whether the magnetic flux changes is the fundamental reason for electromagnetic induction.If the magnetic flux changes, an induced electromotive force will be generated in the circuit. If the circuit is closed again, an induced current will be generated in the circuit.
(3) The generation of induced current is just a phenomenon, which indicates that electric energy is being transmitted in the circuit;The induced electromotive force isElectromagnetic induction phenomenonIt means that the circuit has the ability to output electric energy at any time.
(4) When the change of magnetic flux △ φ is the same, the greater the time △ t is, that is, the slower the change of magnetic flux is, the smaller the induced electromotive force E is;On the contrary, the smaller △ t, that is, the faster the magnetic flux changes, the greater the induced electromotive force E.
(5) When the change time △ t is the same, the larger the change amount △ φ, the faster the change of magnetic flux, the larger the induced electromotive force E;On the contrary, the smaller the change △ φ, the slower the change of magnetic flux, and the smaller the induced electromotive force E.[2]
Theory and practice show that when the length of conductor is LUniform magnetic fieldWhen the cutting magnetic induction line moves in, the induced electromotive force generated in the conductor when B, L and v are perpendicular to each other is:
Electromotive force generated in electromagnetic induction phenomenon.It is usually indicated by the symbol E.When the magnetic flux passing through an open coil changes, although there is no induced current in the coil, the induced electromotive force still exists.When a section of conductor is in uniform strengthmagnetic fieldMedium constant speedCutting magnetic induction line movementNo matter whether the circuit is closed or not, the magnitude of the induced electromotive force is onlyMagnetic inductionB、conductorLength L, cutting speed v and angle θ between v and Bsine It is proportional, that is, E=BLvsin θ (θ is the angle obtained by transforming two perpendiculars between B, L and v).
In the conductor barCutting magnetic induction lineWhen the magnetic flux changes in the closed circuit, the induced current can also be generated.
When the circuit is not closed, but the conductor bar cuts the magnetic induction line, although no induced current is generated, there is electromotive force.Because conductor barCutting magnetic induction line movementWhen a large number of free electrons inside have speed, they will be subject to Lorentz force and move towards one end of the conductor bar until enough charges are accumulated at both ends. The electric field force can balance the magnetic field force, and then the electric potential difference will be generated at both ends.
applicationLenz's lawThe current direction can be judged.[3]
2. The magnetic flux passing through the closed circuit changes (if a condition is missing, there will be no induced current)
Relevant rules
(1) Right-handed rule
The right-hand rule simply shows how a current carrying wire generates a magnetic field.Extend the right hand so that the thumb is perpendicular to the other four fingers and in the same plane with the palm of the hand. Put the right hand into the magnetic field so that the magnetic induction line passes through the palm of the hand vertically (that is, the palm is facing the direction of the N pole of the magnetic field), and the thumb points to the direction of the conductor movement. Then the direction of the other four fingers isinduced currentDirection of.
(2) Left-handed rule
The left-handed rule reflects the stress of charged particles (current carrying wires) in the magnetic field.Extend the left hand so that the thumb is perpendicular to the other four fingers and is in the same plane with the palm of the hand. Put the left hand into the magnetic field so that the magnetic induction line vertically passes through the palm of the hand, and the four fingers point to the direction of the movement of charged particles (the current refers to), then the direction of the thumb is the direction of the force on the conductor.
