
28-16 Electrical Variables
whichcan make them unsuitable for many circuits. For most capacitors, the change in insulation
re
sistance
is an ex
ponential
fu
nction
of te
mperature
(R
T1
= R
T2
e
K(T1−T2)
). is can be substantial in high-
temperature
op
erations
. e te
mperature
de
pendence
of in
sulation
re
sistance
of co
mmon
ca
pacitors
is shown inFigure 28.8.
Frequency and impedance: Practical capacitors have increases in losses at very low and at very high fre-
quencies. At low frequencies, the circuit becomes entirely resistive and the dc leakage current becomes
eective. At very high frequencies, the current owing through the capacitor become importa