Mutual and Self Inductance?

Question

During a 56 ms interval, a change in the current in a primary coil occurs. This change leads to the appearance of a 6.0 mA current in a nearby secondary coil. The secondary coil is part of a circuit in which the resistance is 12 . The mutual inductance between the two coils is 4.1 mH. What is the magnitude of the change in the primary current?

Answer 1

Using the Coupling Formula:

V = -M * dI/dt

So it would appear that your 72mV induced voltage would require 72/4.1 mV/mH of rate of current change or about 18Amps/second.
In this instance this gives the primary current as 18Amps/sec * 0.056seconds which is 1.0 Amps approximately.

You should work out the actual value yourself and set out your answer in a logical manner and explain each step in your calculation so your lecturer can understand how you arrived at your answer.


By LeChatalier's Principle the system moves in such a way as to oppose changes. The induced current occurs through the mediation of an induced magnetic flux - measured in SI in AmpereTurns. The changes in currents in the Primary and Secondary coils will thus produce equal and opposite changes in the magnetic flux in the core. Always consider this basic tenet whenever you have transformer problems. It makes it all easier to understand. It doesn't help much in this case though!!!!

Answer 2

you're no longer thinking the course or component to the precipitated voltages. start up off with merely the standard coil. you're treating the present in the process the standard loop and the generator e.m.f. as though they have been 2 autonomous variables. they do no longer look to be. The voltage which you practice around the 1st coil *reasons* the present to bypass. the present will produce a changing magnetic flux, which will set off an e.m.f. interior the coil. however the precipitated e.m.f. interior the standard coil *opposes* the utilized voltage from the generator and limitations the present flowing. Now wind on the secondary coil. If the terminals of the 2d coil are no longer linked to something then there will be a voltage in the process its terminals subsequently changing flux, yet for sure no present day flowing by that 2d coil. the standard circuit isn't disturbed. If the two coils have the comparable style of turns, then the flux produced by ability of the present flowing interior the 1st coil is going to produce the comparable voltage that the generator is employing to the 1st coil. in case you presently practice a load resistor to the 2d coil, the voltage in the process it is going to consequence in a bypass of present day in the process the 2d coil. which will consequence in its very own magnetic flux, yet back this is the course or component to that flux relative to that produced by ability of the standard coil for you to evaluate. This new flux reduces the internet flux interior the middle, which reduces the e.m.f. precipitated interior the standard coil. (keep in mind that the precipitated e.m.f. interior the standard coil is opposing the present bypass interior the standard.) the end result's that the standard coil present day will enhance till a clean equilibrium is reached. this is a complicated tale. Sorry if that has muddied the waters much greater! :)