Transformer losses:

If the primary coil is not wound on a core of the transformer, we cannot connect to the power source as it will be shorted, but the same coil is wound on a transformer core and connected to the power source it will not be shorted.Though the secondary circuit is open.

As the primary circuit is energized magnetic flux is formed in the core and there is no shorting at the primary connection.

If we cut the core into 2 pieces then what happens to the primary circuit (Magnetic flux distrubed)

Can someone please explain how this happens?

Figure for the question: Circuit

  • \$\begingroup\$ Where do you cut the core into two pieces? \$\endgroup\$ Commented Aug 6, 2014 at 10:25

1 Answer 1


No that's incorrect what you say - you can have an "air-cored" transformer and I see these at VHF frequencies - the down side is that the magnetic flux produced doesn't all couple thru to the secondary but this usually isn't a problem because the transformer in this application is coupling signals and usually has a screened can around the windings to curtail the physical extremities that the flux can reach i.e. it prevents coupling to other parts of the circuit.

So, a coil that doesn't use a core has a much lower inductance but this inductance is never zero and can be quite substantial. Consider the tesla coil: -

enter image description here

Or maybe this: -

enter image description here

On a transformer with an air-gap (as you said "cut the core into 2 pieces"), the net permeability of the core will be reduced and primary inductance will reduce (for the same number of turns) but, you will find that in power applications, core saturation can be avoided compared to a solid homogeneous core.

enter image description here

See also this site for a fuller explanation if you need it. It's also where the picture above came from.

  • \$\begingroup\$ Got an idea, thanks, further how come a coil without core will be blown out,and if it has a core it will sustain.Coil without core acts as a heating coil,but with a core inside it will become a magnet and work done is so much different in heater it is very high and in the core it is negligible \$\endgroup\$ Commented Aug 7, 2014 at 6:38
  • \$\begingroup\$ No, no, no you haven't got the idea - current flow creates magnetism and a suitable core magnifies the field. A permanent magnet is magnetic because of the electrons spinning in the same direction in all the iron atoms and not because iron is somehow good for magnetism. \$\endgroup\$
    – Andy aka
    Commented Aug 7, 2014 at 7:17

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