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You wish to use #18 tungsten wire at 20°c to make a 10 ω resistor. what length of wire will be required for this job? (round the final answer to two decimal places.)

User Cookandy
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1 Answer

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The #18 tungsten has a radius of
r=5.1\cdot 10^(-4)m. The resistivity of the tungsten at
20^(\circ) is
\rho=5.6\cdot 10^(-8) \Omega m. The formula that relates resistance and resistivity is

R=\rho (L)/(\pi r^2)
where L is the length of the wire and
\pi r^2 its section. Therefore, we can calculate L:

L= (R \pi r^2)/(\rho)= (10\Omega \cdot \pi (5.1\cdot 10^(-4)m)^2)/(5.6\cdot 10^(-8) ) =145.8 m
User RomualdM
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