V.3 No 1

73

Several experiments studying dynamic magnetic field

2. Experimental study of phase characteristics of induced emf in the air-core transformer

2.1. Substantiation of the experimental study

As an introductive experiment, let us study a trivial model of air-core transformer.

If we take a turn of wire and conduct along it an alternating current, we know that in the space around this wire there will form a time-alternating magnetic field whose field lines will have the shape shown in Fig. 1 taken from the Berkeley physics course [2, p. 247, Fig. 7.16].

Fig. 1. The alternating current in the coils produces the magnetic field alternating in the centre with 50 Gauss amplitude. At any instant of time within the circle C (blue loop) the field is approximately homogeneous [2, p. 247, Fig. 7.16]

Let us draw our attention to Purcell's remark that the field within the circle C is homogeneous (further this information will be necessary for us) and to typical shape of closed force lines of alternating magnetic field well seen in this figure. Let us pay attention also that the shown structure of field is commonly accepted and fully repeats, e.g., the field structure in the loop inductance, as it is shown in Fig. 2 [3, p. 432, Fig. 537].

Fig. 2. The pattern of lines of force at some instant of time within and around the inductance of electric LC loop [3, p. 432, Fig. 537]