From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Explanation of magnetic principles using a soft iron ring, covering magnetisation and the effect of creating a gap.
| Identifier | ExFiles\Box 35\1\ scan 177 | |
| Date | 11th August 1920 | |
| B. R.{Sir Henry Royce} 29A/100 T: (S. H.{Arthur M. Hanbury - Head Complaints} 159, 11-8-20) G 2250 -7- Contd. To assist in fixing the ideas, consider a soft iron anchor ring wound uniformly with a layer of wire through which an electric current passes. There is magnetic force H due to the current, in the space occupied by the ring, which is of exactly the same value (in this case) as it would be if no iron were present. There is magnetisation M in the material of the ring itself. There is induction B where B = H + M = induction + induction in space in material. Now stop the current and H disappears, but a very large proportion of M remains. There is also no demagnetising force, because the ring is complete and there is no free magnetism. But there is magnetisation, although it has no external effect. If now we take the ring and make a saw cut in it, across a cross section, magnetic polarity appears upon the faces of the cut, and an external magnetic field of force exists due to this polarity. This field is only in the same direction as tje original magnetising field due to the current, in the space of the gap itself, at all other points in the material it opposes the original field, and therefore acts as a demagnetising influence on the ring. The strength | ||