Question

The resistance of copper motor winding at t=20°C is 3.42 Ω. After extended operation at full load, the motor windings measures 4.22 Ω. If the temperature coefficient is 0.0426, what is the rise in temperature?

(a) 60°C

(b) 45.2°C

(c) 72.9°C

(d) 10.16°C

The question was posed to me by my school principal while I was bunking the class.

I want to ask this question from Problems Involving Dot Conventions in division Resonance & Magnetically Coupled Circuit of Network Theory

Answer 1

Right option is (d) 10.16°C

Explanation: Given that, R1 = 3.42 Ω

T1 = 20° and α = 0.0426

R2 = 4.22 Ω

Now, \(\frac{R_1}{1 + αT_1} = \frac{R_2}{1 + αT_2}\)

Or, \(\frac{3.42}{1 + 0.0426 × 20} = \frac{4.22}{1 + 0.0426 T_2}\)

∴ Rise in temperature = T2 – T1

= 30.16 – 20

= 10.16°C.