Zhengzhou wt working time photography

(1) The solar water heater uses solar energy to heat water, so that the internal energy of water increases and the temperature rises, and the solar energy is converted into the internal energy of water.

(2)Q Tai = 8.4× 104j×60min = 5.04× 106j

Q absorption =50%×Q Thai = 0.5× 5.04×106j = 2.52×106j.

From q absorption =cm(t-t0), we get:

T=Q absorption cm+t0 = 2.52×106j4.2×103j/(kg? ℃)×40k g+20℃= 35℃；

(2) From the topic, W=Q =2.52× 106J=7kW? H=7 degrees;

∫P = Wt，

Working time of electric heater:

t=WP=7kW？ h 1kW=7h。

(4) Because black has the best heat absorption effect, the solar heat absorption plate should be black.

Therefore, the answer is: within (1);

(2) The water at 20℃ in the make-up water tank is heated for 65438+/-0 hours with a heat absorption plate, and the water temperature is 35℃;

(3) Power consumption is 7 degrees, which takes 7 hours;

(4) black; Black has the strongest heat absorption capacity.