a) A 33.9-m length of copper wire at 20.0°C has a radius of 0.23 mm. What is the

Question

a) A 33.9-m length of copper wire at 20.0°C has a radius of 0.23 mm. What is the resistance of the wire? Use the table.

b) If a potential difference of 7.0 V is applied across the length of the wire, determine the current in the wire.
c) If the wire is heated to 38.0°C while the 7.0-V potential difference is maintained, what is the resulting current in the wire?

Resistivities and Temperature Coefficients of Resistivity for Various Materials (at 20° Temperature Coefficient Resistivity of Resistivity Material (· m) [(°C)- Silver 1.59 x 10-8 3.8 x 10-8 Copper 1.7 X 10-8 3.9 x 10-8 Gold 2.44 X 10-8 3.4 X 10-8 Aluminum 2.82 x 10-8 3.9 x 10-3 Tungsten 5.6 X 10-8 4.5 X 10-8 Iron 10.0X 10-8 5.0 x 10-8 Platinum 11 x 10-8 3.92 x 10-9 Lead 22 x 10-8 3.9 x 10-8 Nichromea 150 x 10-8 0.4 X 10-8 Carbon 3.5 x 10-5 -0.5 X 10-8 Germanium 0.46 -48 x 10-8 Silicon 640 -75 X 10-8 Glass 1010_1014 Hard rubber =1013 Sulfur 1015 Quartz (fused) 75 x 1016 A nickel-chromium alloy commonly used in heating elements,

Explanation / Answer

(A) R = rho L / A

R = (1.7 x 10^-8) (33.9) / (pi (0.23 x 10^-3)^2 )

R = 3.47 ohm

(B) I = V / R = 7 / 3.47 = 2.02 A  

(C) R= R0 [ 1+ alpha deltaT ]

R = 3.47[ 1 + (3.9 x 10^-3)(18)]

R = 3.711 Ohm

I = V / R = 7 / 3.711 = 1.89 A

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