4. A copper kettle of mass 1 kg contains 0.9 kg of water at 15°C. It takes 12 minutes to rise the temperature to 95°C. If the electric energy is supplied at 220V, calculate the electric current, assuming 10% of heat is wasted. Given specific heat of copper = 420 J kg-K-1 and specific heat of water = 4200 J kg-1 K-1.​

Consider the growth of a 20-nm-diameter silicon nanowire onto a silicon wafer. the temperature of the wafer surface is maintained at 2400 k. assume the thermal conductivity of the silicon nanowire is 20 wm-1k-1 and all its surfaces including the tip are subjected to convection heat transfer with the coefficient h = 1×105 wm-2k-1 and t∞ = 8000 k. when the nanowire grows to l = 300 nm, what is the temperature of the nanowire tip (t (x =