PROBLEMS 57would not drop by more than 2% with respect to
the source open-circuit voltage.*1.2.12A practical current source is represented by an
ideal current source of 200 mA along with a shunt
internal source resistance of 12 k. Determine the
percentage drop in load current with respect to the
source short-circuit current when a 200-load is
connected to the practical source.
1.2.13Letv(t)=Vmaxcosωtbe applied to (a) a pure
resistor, (b) a pure capacitor (with zero initial ca-
pacitor voltage, and (c) a pure inductor (with zero
initial inductor current). Find the average power
absorbed by each element.
1.2.14Ifv(t)= 120
√
2 sin 2π× 60 tV is applied to
terminalsA–Bof problems 1.2.5, 1.2.6, 1.2.7, and
1.2.8, determine the power in kW converted to heat
in each case.
1.2.15With a direct current ofIA, the power expended as
heat in a resistor ofRis constant, independent of
time, and equal toI^2 R. Consider Problem 1.2.14
and find in each case the effective value of the
current to give rise to the same heating effect as in
the ac case, thereby justifying that the rms value
is also known as the effective value for periodic
waveforms.
1.2.16Consider Problem 1.2.14 and obtain in each case a
replacement of the voltage source by an equivalent
current source at terminalsA–B.
1.2.17Consider Problem 1.2.5. LetVAB=120 V (rms).Show the current and voltage distribution clearly
in all branches of the original circuit configuration.
*1.2.18Determine the voltagesVxusing voltage division
and equivalent resistor reductions for the circuits
shown in Figure P1.2.18.
1.2.19Find the currentsIxusing current division and
equivalent resistor reductions for the networks
given in Figure P1.2.19.
1.2.20Considering the circuit shown in Figure P1.2.20,
sketchv(t) and the energy stored in the capacitor
as a function of time.
1.2.21For the capacitor shown in Figure P1.2.21 con-
nected to a voltage source, sketchi(t) andw(t).
*1.2.22The energy stored in a 2-μF capacitor is given by
wc(t)= 9 e−^2 tμJ fort≥0. Find the capacitor
voltage and current att=1s.
1.2.23For a parallel-plate capacitor with plates of area
Am^2 and separationdm in air, the capacitance
in farads may be computed from the approximate
relationC≈ε 0
A
d
=
8. 854 × 10 −^12 A
d
Compute the area of each plate needed to develop
C=1 pF ford =1 m. (You can appreciate
why large values of capacitance are constructed
as electrolytic capacitors, and modern integrated-
circuit technology is utilized to obtain a wide va-
riety of capacitance values in an extremely small
space.)(a)1 Ω
3 Ω2 Ω2 Ω Vx−++12 V −(b)4 Ω2 Ω 2 Ω
+−
Vx+−15 V(d)4 Ω
1 Ω1 Ω 3 Ω−+
9V(c)3 Ω^2 Ω^2 Ω+−Vx+−6VVx+−Figure P1.2.18