P |
(2) Q water=mc?t=189000J,
W=Pt=550W×6×60s=198000J,
then η=
QI water |
W |
(3) Heating when S is closed, we have:P heating=
U2 |
R2 |
R2 |
U2 |
R1+R2 |
In accordance with the question, there are:P insulation=
1 |
2 |
Solve:
R1 |
R2 |
1 |
Answer: (1) The current during normal operation is 2.5A; (2) The efficiency of the water dispenser is 95%; (3) The ratio of the two resistors is 1:1.