What will be the maximum magnetic strength to which a piece of ferromagnetic substance can be magnetised?

What will the maximum strength possible for a piece of iron?

How would the shape of the ferromagnetic substance affect this strength?

What would be the current needed in the solenoid if this strength is to be achieved?

  • $\begingroup$ For the solenoid part, assume the dimensions and mention them. $\endgroup$ – karthikeyan May 20 '14 at 14:19

The effect you're describing is called magnetic saturation. This is the point where increasing the external magnetic field doesn't increase the magnetisation of your ferromagnet becaused all the domains are aligned and no further increase in the net alignment is possible.

Iron saturates at around 2 Tesla. This is a property of the material so the shape of the piece of iron doesn't make any difference.

The field at the centre of solenoid is $B = \mu n I$, and the graph in the linked article shows the required values of the product $nI$. For most materials it's some where in the range $nI = 50 - 100$ amp turns per inch.

  • $\begingroup$ The strength of 2T that you say is for any size or unit volume or something like that? $\endgroup$ – karthikeyan May 20 '14 at 15:11
  • $\begingroup$ @karthikeyan: a Tesla is the field density i.e. the field per square metre. $\endgroup$ – John Rennie May 20 '14 at 16:18
  • $\begingroup$ I was asking about the size of iron. $\endgroup$ – karthikeyan May 20 '14 at 16:50
  • $\begingroup$ @karthikeyan: the size of the piece of iron doesn't matter. Since the field strength is magnetic flux per unit area a larger piece of iron will have more flux flowing through it and the flux per unit of iron is constant. $\endgroup$ – John Rennie May 20 '14 at 16:52
  • $\begingroup$ So you mean to say, an arrangement like N-S-N-S of two magnets wont compound magnetic field strenght(B)a the poles? I was thinking in that line all the time..(similar to voltages adding up in series) $\endgroup$ – karthikeyan May 20 '14 at 17:05

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