Fig. 3.92.3.321. Calculate the inductance of a unit length of a double tape
line (Fig. 3.92) if the tapes are separated by a distance h which is
considerably less than their width b,
namely, b/h = 50.
3.322. Find the inductance of a
unit length of a double line if the
radius of each wire is II times less
than the distance between the axes
of the wires. The field inside the
wires is to be neglected, the per-
meability is assumed to be equal
to unity throughout, and fl >> 1.
3.323. A superconducting round
ring of radius a and inductance L
was located in a uniform magnetic field of induction B. The ring plane
was parallel to the vector B, and the current in the ring was equal to
zero. Then the ring was turned through 90° so that its plane became
perpendicular to the field. Find:
(a) the current induced in the ring after the turn;
(b) the work performed during the turn.
3.324. A current / 0 = 1.9 A flows in a long closed solenoid.
The wire it is wound of is in a superconducting state. Find the
current flowing in the solenoid when the length of the solenoid is
increased by /I -=-- 5%.
3.325. A ring of radius a = 50 mm made of thin wire of radius
b = 1.0 mm was located in a uniform magnetic field with induction
B = 0.50 mT so that the ring plane was perpendicular to the vector B.
Then the ring was cooled down to a superconducting state, and the
magnetic field was switched off. Find the ring current after that. Note
that the inductance of a thin ring along which the surface currentflows is equal to L = u 0 a In 7 8a ,- - 2).
3.326. A closed circuit consists of a source of constant em1 g and
a choke coil of inductance L connected in series. The active resistance
of the whole circuit is equal to R. At the moment t = 0 the choke
coil inductance was decreased abruptly times. Find the current in
the circuit as a function of time t.
Instruction. During a stepwise change of inductance the total
magnetic flux (flux linkage) remains constant.
3.327. Find the time dependence of the current flowing through
the inductance L of the circuit shown in Fig. 3.93 after the switch
Sw is shorted at the moment t = 0.
3.328. In the circuit shown in Fig. 3.94 an emf V, a resistance R,
and coil inductances L 1 and L 2 are known. The internal resistance of
the source and the coil resistances are negligible. Find the steady-
state currents in the coils after the switch Sw was shorted.
3.329. Calculate the mutual inductance of a long straight wire and
a rectangular frame with sides a and b. The frame and the wire lie