A 0.19 mm diameter copper wire is 14 m long. Part A Find its resistance. Express

Question

A 0.19 mm diameter copper wire is 14 m long.

Part A

Find its resistance.

Express your answer to two significant figures and include the appropriate units.

Part B

Whats the power dissipation in the wire if the potential difference across its ends is 10 V ?

Express your answer to two significant figures and include the appropriate units.

Part C

Repeat part (a) if the wire is immersed in liquid nitrogen at 77 K.

Express your answer to two significant figures and include the appropriate units.

Part D

Repeat part (b) if the wire is immersed in liquid nitrogen at 77 K.

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

Resistivity of copper changes linearly with temperature down to about 77K: the temperature coefficient of resistivity is about 0.0039 K^(-1). At 293K, the resistivity is 1.68 x 10^(-8) ohm*meter, so at 77K it should be

rho = 1.68x10^(-8) ohm*m * (1 - 216*0.0039)
= 2.65 x 10^(-9) ohm*m

Then use R = (rho * L) / A
where L = 14 m and A = pi(0.0019 m)^2

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