Created it, 05/10/15
Update it, 05/11/22
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ELECTROMAGNETIC INDUCTION “2nd PART”
Initially, we must know if the reel is a wasteful element of electric power as well as resistance or, on the contrary a preserving element of electric power like the condenser.
To facilitate our task, we must consider the phenomenon of the mutual inductance which, let us recall it occurs between two distinct circuits.
Figure 11 represents a primary circuit and an induced circuit.
The current induces I2 appearing in the whorl of the induced circuit crosses the resistance inserted in this circuit: this one thus dissipates a power determined by the product of resistance R by the square of the current (I22).
This power cannot however be directly produced by the induced circuit since we do not note the presence of any generator in this one. The single generator present is the pile of the primary circuit, but this pile is not connected to the induced circuit. The transfer of energy between the two circuits is thus carried out by the flow of induction which the two whorls share.
We must then admit that the electric output provided by the pile to the primary circuit is not completely dissipated in this one but also not produced a flow of induction which is in its turn retransformé in electric output dissipated in the induced circuit. We can conclude that the reel is a preserving element of energy like the condenser since it entirely does not dissipate this energy.
To have a narrower analogy with the condenser, we can say: as the condenser stores electric power by creating an electric field between its reinforcements, the reel stores the electric power by creating a magnetic field around its whorls. For the difference of the condenser for which it is necessary to apply a tension between its reinforcements to create an electric field, it is necessary to make circulate a current in a reel so that this one generates a magnetic field.
We know that energy Wc stored in a condenser depends on the square of the tension applied between its reinforcements and the capacity of the condenser, that is to say :
In the same way, the energy stored by a reel depends on the square of the current which crosses it multiplied by the inductance of this reel, the whole divided by 2, that is to say :
WL : Electric power stored in J.
L : Inductance out of H
I : Intensity in A
In a way similar to what was known as for the condenser, the reel stores only one half of the energy provided by the generator. Second half is dissipated in resistance equivalent to the circuit to which belonged inter alia internal resistance of the generator.
Let us observe however that in the case of the condenser, the generator provides a current only during the load of the condenser, because once this one charged, any circulation of current ceases, as any dissipation of energy to which it gives place. In the case of the reel, the current must circulate continuously since it is precisely him which creates the magnetic field in the reel by its variations. The consumption of energy accompanying it thus persists also.
We deduce from these observations which the reel consumes an energy more important than the condenser to store the same quantity of it.
The reel finds its employment in the circuits traversed by fluctuating currents.
In the next lesson, we will analyze this type of current, of which one of the forms is particularly familiar for you since it is about the AC current.
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