Question

A coil of Nichrome wire is 28.0 m long. The wire has a diameter of 0.450 mm and is at 20.0

Answer 1

resistivity of Nichrome is rho = 1*10^-6 ohm m

given length L = 28 m

area A = pi r^2     = 3.14* 0.225 e-3 *0.225e-3

A = 1.6 e-7 m^2

so

use the equation Current density J = i/A = E/rho

so

so Electric field E = i rho/A

E = 0.4 * 1 e-6/(1.6 e-7)

E = 2.5 N/C

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Resistance R = rho L/A

R = 1.e-6*28/(1.6 e-7)

R = 175 Ohms

so Power P = i^2R

P = 0.4*0.4*175

P = 28 Watts

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when T = 320 deg

Rt = Ro (1+ A DT)

A of Nichrome is 0.0004

here DT = 360-20 = 340 deg

so

Rt = 175 *(1+ (0.0004 * 340))

Rt = 198.8 ohms

so

POwer P = 0.4*0.4*198.8

P = 31.808 Watts