254 Chapt. 33 Alternating Current or AC
power equality result to derive the relationship between the primary current
I
p
and the
secondary current
I
s
. Assume that the power in both coils obeys
P
=
I
Δ
V ,
where
I
is the current through the device and Δ
V
is the potential change across the device
(which for ideal coils is the emf).
c) Find the formula that relates
N
p
,
I
p
N
s
, and
I
s
. Then give a combined ratio formula for
number of coil turns, coil emfs, and coil currents.
033 qfull 00610 1 3 0 easy math: transformer power e±ciency
4. Using high transmission potential and low transmission current is energy e±cient: their is less
energy lost in heating the transmission wires.
a) A power station outputs power
P
at (RMS) potential
E
. The transmission wire has
resistance
R
. The power lost to heat in the wire is
P
loss
Find the formula for relative
power loss
P
loss
/P
in terms of
P
,
R
, and
E
.
HINT:
Assume potential and current are in
phase: i.e., assume that the formula
P
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 Fall '06
 Buchler
 Physics, Current, Power, Alternating Current, 1.2 MW, relative power loss, 10.0 km

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