In the experiment (1), using an electric heater instead of an alcohol lamp to heat the inside of the liquid and using a closed flask instead of an open beaker can reduce the heat loss of the liquid and reduce the error.

(2) The two liquids A and B have the same mass, the same initial temperature and the same heat absorption. According to Q=cm△t, judge whose temperature is high, whose temperature changes greatly and whose specific heat is small at the same time.

(3) When the switch is closed, it is found that the thermometer reading of bottle B rises slower than that of bottle A, so it can be judged that the temperature of bottle A changes greatly. The two liquids A and B have the same mass, the same initial temperature and the same heat absorption. According to Q=cm△t, it can be judged that the specific heat capacity of liquid B is greater than that of liquid A. 。

(4) As shown in the figure, A and B are connected in series in the circuit, the current is equal, the power-on time is the same, and R A > R B, so we can explore the relationship between the heat generated by current and resistance, and the process of generating heat by current is the process of doing work by current.

So the answer is: (1) reduce heat loss; (2) quality; (3) large; (4) resistance.