How Does EMF Induce in a Solenoid Despite Minimal Flux Cutting?

[QwertyXP]

1. Assuming that both the windings of a transformer is wrapped around an iron core, how is an EMF induced in the secondary winding - isn't it necessary for flux to cut through the winding in order to induce an EMF? The flux cutting through the winding would apparently be very low..as most of it is contained inside the iron core.

2. If a magnet approaches a solenoid along its horizontal axis, the flux cutting through the solenoid will increase. However, the motion is parallel to the direction of magnetic field. Will an emf be induced across the solenoid?

 

[skeptic2]

The flux of a solenoid must complete a loop. Yes the flux inside the solenoid is largely contained in the iron core. However the flux also leaves the iron core and completes its loop outside the solenoid. When the field is reversed, it must pass through the windings inducing a current.

Do you mean if a magnet approaches a solenoid in line with the coil and perhaps even enters the solenoid? If so, then consider the magnetic field a torus and you will see that the field must cross the windings. If the magnet approaches the solenoid perpendicular to the center of the coil, the flux lines will cross the windings but the field intersecting the coil on one side of the coil will cancel the field on the other side and very little current will be induced.

 

[QwertyXP]

Thanks, skeptic2.

I didn't get the first point. As most of the flux from the primary remains inside the iron core while completing its loop and very little of it cuts the secondary winding (in an ideal transformer all the flux should remain inside the core), very little power should be transferred to the secondary winding - but in a transformer nearly all the power from the primary is transferred...?

Magnet approaching a solenoid in line with the coil: i think I've understood. The magnetic field is torroidal and hence even when the magnet is far away, the field lines cutting through the upper portion of the solenoid coil would be tilted slightly upwards and those passing through the lower portion would have a slight downward direction. Is that what u meant to say?

 

[skeptic2]

As most of the flux from the primary remains inside the iron core while completing its loop and very little of it cuts the secondary winding (in an ideal transformer all the flux should remain inside the core), very little power should be transferred to the secondary winding - but in a transformer nearly all the power from the primary is transferred...?

Not only must the flux complete a loop, the loop must contain the windings with the current that creates the flux. In other words the loop must go around the windings. The loop of the flux cannot be completely contained by a core that only passes through the center of the solenoid.

 

[alphy]

I can explain the phenomenon of EMF induction in a solenoid using the principles of electromagnetic induction. In order to understand how EMF is induced in the secondary winding of a transformer, it is important to first understand the concept of magnetic flux.

Magnetic flux is a measure of the strength of a magnetic field passing through a given area. When a varying magnetic field passes through a conductor, it induces an electric current in the conductor. This is known as electromagnetic induction.

In a transformer, the primary winding is connected to an AC power source, which creates a varying magnetic field. This varying magnetic field then passes through the iron core, which concentrates and strengthens the magnetic field. As a result, the flux passing through the secondary winding is also increased.

Now, to address the first question, it is true that the majority of the flux is contained within the iron core. However, some of the flux still passes through the secondary winding, albeit at a lower magnitude. This is because the iron core is not a perfect conductor and has some resistance, which causes some of the flux to leak out and pass through the secondary winding. This is what induces an EMF in the secondary winding.

Moving on to the second question, the motion of a magnet approaching a solenoid along its horizontal axis will indeed increase the flux passing through the solenoid. This is because the magnetic field of the approaching magnet is perpendicular to the direction of the solenoid, and therefore, the flux cutting through the solenoid will increase. This increase in flux will induce an EMF in the solenoid, even though the motion is parallel to the direction of the magnetic field.

In conclusion, EMF induction in a solenoid is a result of the principles of electromagnetic induction. The varying magnetic field passing through the solenoid induces an electric current in the conductor, and this is how EMF is induced in the secondary winding of a transformer.