Test and analysis: from the heating power and working voltage of the soymilk machine, the heating resistance of the soymilk machine is obtained by formula; From the 6th minute to the 9th minute, soybean milk was basically formed. Knowing the quality and specific heat capacity of soybean milk, the temperature change is obtained from Figure C, and the heat absorbed by soybean milk is obtained by using the endothermic formula Q absorption =cm△t; As can be seen from Figure B, electric heating tube's working time and motor's working time when the soymilk machine works normally once, and the electric energy consumed by the soymilk machine when it works normally once are calculated by W=Pt.
Solution: (1) According to the topic, heating power p1=100w, U=220V,
∵, ∴ heating resistance of soybean milk machine:
;
(2) Heat absorbed by soybean milk:
Q suction =c soybean milk m△t=4.0× 10 3 J/(kg? ℃)× 1.5kg×( 100℃-70℃)= 1.8× 10 5j；
(3) As can be seen from the image, the soymilk machine works normally once, the working time of the electric heating tube is t1=1min, and the working time of the motor is t 2 =2min.
The electric energy consumed by the soymilk machine when it works normally;
w = P 1t 1+p2 T2 = 1 100 w× 1 1×60s+200 w×2×60s = 7.5× 10 5j。
Answer: (1) The heating resistance of soymilk machine is 44Ω;
(2) From the 6th minute to the 9th minute, the heat absorbed by soybean milk was1.8×105j;
(3) The soymilk machine works normally to make soymilk once, and the total power consumption is 7.5× 105J.
Comments: This topic is the comprehensive calculation of electricity and heat. Examine students' mastery and application of electric power formula and its deformation formula, W=Pt and endothermic formula. The key is the flexible use of the formula and its deformation. The difficulty lies in finding the working time of the electric heating tube and motor when the soymilk machine works normally. Learn to find useful data from the information given in the topic, and pay attention to the conversion of units in the process of solving problems.