phy 問題

Specific Heat Capacity of Water =4200 J kg-1 oC-1
Specific latent heat of vapourization of water= 2,260,000J kg-1
Heat(Energy) from the heater: 1000x10x60=600,000J
Heat gained by he water before boiling = 0.5x4200x(100-20)= 168,000J

Heat(Energy) used to boil water = 600,000-168,000 =432,000J
Mass of water boiled = 432,000/2,260,000 = 0.19115044kg
所以答案係A。
以上Assume左no energy lost。
解釋︰(In English)
The energy given by the heater is more than the energy to increase the temperature of water from 20 degree calcius to 100 degree calcius. Therefore, there will be energy in exist, the energy then makes the water to become vapourized. As no surronding energy will be gained (surrounding tempeerature is lower). If there is really no energy lost, all the energy left after increasing the temperature of water to 100 degree calcius will be used to vapourized.
By Energy= mass x Specific Latent heat of vapourization
Therefore, the maximum mass is calculated as the energy is in maximum.