Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

268 Aptitude Test Problems in Physics

Obviously, if

W2-FW1

R-Fri > R-Fri-Fr^2 '

he answer will be affirmative.
Thus, if the inequality W i (R r2) >
(C-^1 -^ {R^ r^1 ) is^ satisfied, and hence
W 1 r 2 > (R^ r^1 ), the current in the circuit
increases. If, on the contrary, WIr 2 < g 2 (R r 1 ),
the short-circuiting of the current source leads to
a decrease in the current in the circuit.
3.34•. Let us make use of the fact that any "black
box" circuit consisting of resistors can be reduced

r

Fig. 217

to a form (Fig. 217), where the quantities R1,

R 2 ,. ., R5 are expressed in terms of the resist-

ances of the initial resistors of the "black box"

circuit (this can be verified by using in the initial

circuit the transformations of the star-delta type

and reverse transformations). By hypothesis,

equal currents pass each time through resistors

of resistance R 1 and R, and also through R3 and

R5 (or there is no current through them when the

clamps are disconnected). Using this circumstance,

we can simplify the circuit as shown in Fig. 218.

Then, by hypothesis,

Us (^) U 2
Ni — Ri , N2
R; -1- R;R;I(R;+
Us _
Ns
lc-
N4
R;-1- R;R;I(Ri+