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The movable mirror of the Michelson Interferometer is attached to the end of the brass extension of the specimen. As the rod contracts or elongates, the interference fringes shift across the field of view. The change in length of the ferromagnetic rod may thus be measured in terms of wave-lengths of light.
When the rod
As the rod
Any change in the length of
Bidwell’s method involved the measuring of the change in the diameter of the toroid which he used. Any change in the diameter of
Showing the relations between the longitudinal and transverse Joule magnetostrictive effects.
The upper half of the bar is stretched and the lower half is compressed.
Showing the direction of the resultant magnetic field when a circular and a longitudinal magnetic field are superimposed on each other.
The twisting of the rod
As the volume of R changed due to magnetic field, the water surrounding the specimen would be forced up or down the capillary tube and so the change in volume measured. A, S are the rings and supports which held the specimen in place while being magnetized.
Magnetization of annealed iron under various amounts of longitudinal pull.
This graph illustrates the way in which various ferromagnetic substances change their length in a magnetic field. All values above the zero line represent contraction and all below indicate an elongation of the specimen.
In the ballistic method the coil C is attached to a ballistic galvanometer and the inductive throw taken when the rod is stretched and again when unstretched. Without removing the rod the magnetization of the rod may be followed in the streteched and unstrectched condition by means of the magnetometer M. S is the coil for compensating the field due to the solenoid S.
2nd Wiedemann Effect; When an electric current flows through the rod, R, it is magnetized circularly. Twisting the rod in this condition sets up a longitudinal magnetization which induces a current in the coil S.
By means of the coupling C the cell containing the specimen R is connected to a compressor and the water forced in around R. This hydrostatic pressure changes the volume of R and in consequence the magnetic induction is also changed.
Two cells with specimens just as near alike as possible are arranged symmetrically on either side of a magnetometer. When the magnetometer has been balanced, pressure is put on one of the specimens and the sensitive magnetometer indicates the difference in magnetic induction due to pressure. The two cells and specimens are built as indicated in Fig. 16.