phy 物理 heat

Are you asking 96 Q 20?
It is an experiment finding the specific latent heat of vaporization.
( 1 ) is wrong because you want the water to vaporize but if you cover the beaker of water with a lid, then water will condense back to the beaker. Thus the accuracy will be lowered instead of improved.
Covering with a lid can only reduce errors when you want to find the s.h.c. of water.
( 2 ) is definitely correct as this can reduce the heat loss to the surrounding.
( 3 ) is only suitable if you are going to measure liquid temperature. Then a stirrer can ensure a uniform liquid temperature. However, this experiment does not have such requirement.
Hence the answer is ( 2 ) only.

2008-04-09 21:49:29 補充：
Sorry for a typing error: [steam] will condense back to the beaker.

個實驗搵咩先??比潛熱??