NDT TEST-Electromagnetic induction

1. Electromagnetic induction
When the magnetic flux passing through the area enclosed by the closed conductive loop changes, an induced current is generated in the loop. This phenomenon is called electromagnetic induction. The induced electric potential Ei generated in the loop is equal to the negative value of the magnetic flux φ in the enclosed area with time.
Ei=-dф/dt


This negative value indicates that the magnetic field generated by the induced current in the closed loop always hinders the change of the magnetic flux that generates the induced current. This equation is called the Faraday electromagnetic induction theorem. This equation is used for a coil with N匝, and the resulting induced electromotive force is expressed as
Ei=-N(dф/dt)=-d(Nф)/dt
Ei volts, N 匝, ф Weber, t seconds


2. Self-induction
When the alternating current I is passed through the coil, the alternating magnetic flux generated by it will also generate an induced electromotive force in the coil. This phenomenon is called self-induction phenomenon, and the induced electromotive force generated is called self-induced electromotive force EL.
EL=-L(di/dt) L Self-inductance coefficient, unit Henry (H)


3. Mutual induction
When the two coils are close to each other and the alternating currents I1 and I2 flow respectively in the coil, the varying magnetic field caused by the current I1 in the coil 1 generates an induced electromotive force in the coil 2 when passing through the coil; likewise, the coil 2 The varying magnetic field caused by the medium current I2 generates an induced electromotive force in the coil 1 as it passes through the coil 1. The phenomenon that the two current-carrying coils excite the induced electromotive force mutually is called a mutual inductance phenomenon.

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