Unformatted text preview: Problem 4
A copper cable is designed to carry a current of 300 A with a power loss of 2.00 W/m. What is
the required radius of this cable? (Resistivity of copper is approximately p =l .7x10"3 am) a) r=0.077m
b) r=7.7x10_4 m
c —l.011 m d r=0.016 m c) r=1.5xlO m Problem 5
A microbiologist measures the total current due to potassium ions (K+) moving through a cell membrane of a rock crab neuron cell to be 30 nA. How many ions pass through the membrane
each second? = a) 2.50 nmole
b) 0.050 pmole
c) 1.88 nmole d) 1.88 mole Problem 6 The resistivity of copper as a function of temperature is given approximately by p = po[1 + a(T-
To)] where p =1.7x10’8 Q-m at T=20 IC and a = 4.3):10'3 C". Find the temperature at which the
copper’s resistivity is twice its room-temperature value. m P=~Vo [HORN—$57 b 50c ‘ .
c) 40c i'7Xln “4.0+ ‘i-3Xlo‘3 (7
d) 486C e) 298C T=- 9" ‘3 +70
dips '.7x'o-8—3.°IKIF3 +23 9% X163 (34 m3) ...
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- Spring '10