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

262 Aptitude Test Problems in Physics

R 3 7

R Ac(D)B

,

T

–

=-- — 8 - R

R(718)R 7 R

Thus, the current I in the leads can be determined

from the formula

1

I — =

5 U

(7/15) R^ 7 R •

3.26*. In order to simplify the solution, we present

the circuit in a more symmetric form (Fig. 213).

The obtained circuit cannot be simplified by con-

necting or disconnecting junctions (or by removing

some conductors) so as to obtain parallel- or series-

connected subcircuits. However, any problem

involving a direct current has a single solution,

which we shall try to "guess" by using the sym-

metry of the circuit and the similarity of the cur-

rents in the circuit.

Let us apply a voltage U to the circuit and mark

currents through each element of the circuit. We

AB 0

Fig. 213

shall require not nine values of current (as in the

case of arbitrary resistances of circuit elements)

but only five values / 1 , 12, I3, I4, and /5

(Fig. 214). For such currents, Kirchhoff's first rule

for the junction C

11.13+15

RAB— R-F(718)R — 15 •