A 2 mm diameter electric wire is insulated with 2 mm thick plastic. The plastic has a thermal conductivity of 0.5 W.m⁻¹.K⁻¹. The wire is exposed to air at 320 K and outside convective heat transfer coefficient is 25 W.m⁻².K⁻¹. Wire surface temperature is constant at 420 K and remains unaffected by the covering. Assuming steady state heat transfer conditions, the ratio of heat loss per metre of wire length with insulation to that without insulation is nearest to
(Take π = 3.14)