A coil has resistance of 18Ω when its mean temperature is 200°C and of 20Ω when its mean temperature is 500°C. What will be mean temperature rise when its resistance is 21Ω and the surrounding temperature is 150°C
(a) 40°C
(b) 50°C
(c) 60°C
(d) 70°C
Correct option(b)
Explanation: