1/Rp 1/R1 +1/R2 +1/R3 +. RsR1 R2 R3+... 1) A household stove has a heating eleme

Question

1/Rp 1/R1 +1/R2 +1/R3 +. RsR1 R2 R3+... 1) A household stove has a heating element that is made of tungsten wire. The temperature coefficient of resistivity is a 4.5 x 103 /°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 1.2 A

Explanation / Answer

9 and 8 ohms are in parallel==> net of this is 9*8/(9+8) = 4.2353

4 and 6 are in series ==> net is 4+ 6 =10

this 10 and 4.2353 are in parallel ==> net = 10*4.2353 /(10+4.2353) = 2.975

this is in series with 3 ====> net is 3+2.975 = 5.975

this is in parallel with 20 ohms=====> equivalent R =20*5.975 / (20+5.975) = 4.6 ohms

if 36 is across it... then it is also across 20 and 3 ohms

so current in 20 and 3 ohms is 36/23 = 1.5652 A

so volatge AB = 36 - 1.5652*3 = 31.304 V

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