Monday, April 9, 2018 Physics 122 Circuits Test Name 1/Rp 1/R, +1/R2 +1/R3 + Rs

Question

Monday, April 9, 2018 Physics 122 Circuits Test Name 1/Rp 1/R, +1/R2 +1/R3 + Rs R1+ R2 +R3 1) A household stove has a heating element that is made of tungsten wire. The temperature coefficient of resistivity is ? 4.5 x 10-3 / °C and the supply voltage is 120 V, when the stove is first turned ON the current is found to be 4.0 A and the initial temperatre of the wire is 38 °C. After heating for a short while the current is found to be reduced. Knowing that the temperature of the wire depends upon the resistance calculate the temperature of the wire when the current is 1.3 A

Explanation / Answer

at T = 38 deg C ,

R0 = V / I = 120 / 4 = 30 ohm

then at T ,

R = 120 / 1.3 = 92.3 Ohm

and R = R0 [1 + alpha deltaT ]

92.3 = 30 [ 1 + (4.5 x 10^-3)(T - 38)]

T - 38 = 462

T = 500 deg C

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