P28_033.PDF

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Chapter 28 - 28.33
33. (a) We note that the R 1 resistors occur in series pairs, contributing net resistance 2 R 1 in each branch
where they appear. Since
E 2 =
E 3 and R 2 =2 R 1 , from symmetry we know that the currents
through
E 2 and
E 3 are the same: i 2 = i 3 = i . Therefore, the current through
E 1 is i 1 =2 i .Then
from V b
V a =
E 2
iR 2 =
E 1 +(2 R 1 )(2 i )weget
i = E 2 −E 1
4 R 1 + R 2 =
2 . 0V
4(1 . 0Ω)+2 . 0Ω =0 . 33A .
4 . 0V
Therefore, the current through
E 1 is i 1 =2 i =0 . 67A, flowing downward. The current through
E 2
is 0 . 33A, flowing upward; the same holds for
E 3 .
(b) V a
V b =
iR 2 +
E 2 =
(0 . 333A)(2 . 0Ω)+4 . 0V=3 . 3V .
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