Bukhovtsev-et-al-Problems-in-Elementary-Physics

344 .
ANSWERS AND SOLUTIONS
Fig. 457
Fig. 458
The field created by the current with a density I at an arbitrary point
of space A is equal to HI=k·2njR (Fig. 456). Here R is the distance from
the axis of the conductor to point A. (It is assumed that the current flows
toward us.)
At the same point, the current flowing through the volume. corresponding
to the space, but in the reverse direction, induces a field of H 2=k·2njr.
Figure 456 shows that the total intensity of the field is
Obviously,
H=VH:+H:-2H 1Ht cos ex
Therefore, the intensity H =k·2njd is the same for all the points of the
space. .
551. Triangle AOC is similar to triangle BAD (Fig. 456) since they have
one equal angle, and the sides confining these angles are proportional.'
Therefore, L AOC=L BAD. But R l..H 1 , and therefore H l..d.
The intensity of the magnetic field at any roint of the space is perpendicular
to the line that connects the centres 0 the conductor and the space.
The distribution of the lines is shown in Fig. 457.
552. k=..!.., where c is the velocity of light in a vacuum.
c
553. No, it will not. Forces of attraction exist between the separate elements
of the current. As a result, the density of the current increases somewhat
toward the axis of the conductor. The effect is negligible.
554. When lightning strikes. a very high current flows for an instant
through the pipe and the separate elements of the current are mutually
attracted with a high force. It is this force that converts the pipe into
a rod.