Question

An iron rod (of density 8 x 10³ kg/m³ and specific heat capacity 0.462 x 10^-3 J/kg°C) is subjected to cycles of magnetissation at the rate of 50 cycles/s. If the area enclosed by B.H curve corresponds to an energy of 10^-2 joule, the rise of temperature per minute (assuming there are no radiation losses) would be

(1) 81°C

(2) 8.1°C

(3) 0.81°C

(4) 16.2°C

Answer 1

(2) 8.1°C

The area enclosed by the B–H curve, equals the energy loss per unit volume per cycle.

∴ The energy loss per unit volume in one second = 10^-2 x 50 J

Hence Q, the heat produced per unit volume in one minute, equals

Q = (10^-2 x 50 x 60)j = 30 J

Let θ be the rise in temperature per unit volume. The mass per unit volume equals ρ , the density. Hence