(2) Current during normal operation:
I = PU = 2000 w220v≈9. 1A;
(3) Heat absorbed by water:
q = cm(t 1-T2)= 4.2× 103j/(kg? ℃)× 1kg×( 100℃-25℃)= 3. 15× 105j,
Electric energy consumed by heating water:
w = Pt = 2000 w× 175s = 3.5× 105j,
Thermal efficiency of induction cooker:
η=Q absorption w = 3.15×105j3.5×105j = 90%.
Answer: (1) Compared with ordinary electric furnaces, induction cookers have higher thermal efficiency;
(2) The current during normal operation is about 9.1a; ;
(3) The power consumption is 3.5× 105J, and the thermal efficiency of the induction cooker is 90%.