Liang Xiao and his father went out to travel and stayed at Xingkai Lake Hotel. The beautiful and exquisite electric kettle in the room attracted Liang Xiao's interest, as shown in Figure A,

(1) The transparent plexiglass tube and the pot body form a communication device. When the water is not flowing, the water surface is flat. We can know the amount of water in the pot by observing the water level in the glass tube and add water in time.

(2) The volume of water in the pot:

v = 1.2L = 1.2× 10-3 m3，

Water quality in the pot:

m =ρv = 1× 103kg/m3× 1.2× 10-3 m3 = 1.2kg，

Heat absorbed by water:

Q suction =cm△t=4.2× 103J/(kg? ℃)× 1.2kg×( 100℃-20℃)= 4.032× 105j；

(3) Electric kettle at rated voltage, P=P quantity = 1500W,

Power consumption when working at rated voltage for 5 minutes:

W electricity = pt =1500 w× 5× 60s = 4.5×105j;

(4) Thermal efficiency of electric kettle:

η= Q- absorption w×100% = 4.032×105j4.5×105j×100% = 89.6%.

Answer: (1) The transparent plexiglass tube and the pot body form a communication device;

(2) The heat absorbed by the water in the kettle is 4.032×105j; ;

(3) The electric kettle works at rated voltage for 5 minutes, and the power consumption is 4.5×105j; ;

(4) The thermal efficiency of electric kettle is 89.6%.