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

ELECTRICITY AND MAGNETISM 359
A ......---...
Fig. 470
B
tude of 180 V) plus the same vol..
tage of the charged eapaeitor. The
change in the potent ia I along the
circuit at this moment of time is
shown in Fig. 470.
If the rectifier operates without
load, the capacitor should be caleufated
for a puncturing volta ge of at
least 180 V, and the diode for a
voltage of at least 360 V.
604. The anode voltage of each
diode is
U a = ~
sin rot-IR
A current flows through the diode when Ua > 0 and does not flow through
it when V a ~ O. In a quarter of a period the current will not flow during
the time interval 0 ~ t ~ t 1 (Fig. 471). where t 1 is determined by the equation
I/o
-JH
Fig. 471
~ sin rot.-IR=0. Hence, t. = ~ arc sin 2~R . This is also the time during
which the current does not flow in the following quarters of the period.
Altogether in a period the current does not flow during
2T . 2/R
"""it arc sin ---0-=0.465 T
3-6. Electrical Machines
605. If the frequency of the alternating current remains the same, this
means that the revolutions of the motor and the generator also remain as
before. and the e.rn.I. of the generator wHI not change.
When the external resistance in the circuit is high, the circuit will carry
a smaller current and a lower power will be supplied. For this reason the
power of the motor that revolves the generator should be reduced.
606. The work performed by a field in moving conductors carrying a current
(armature windings) is not equal to the total work of the field. Apart from
the work spent to move the conductors, the magnetic field performs work to