Physics-specific latent heat

2009-11-05 2:46 am

1.The apparatus is used to measure the specific latent heat of ice.
-heat: 60W
-melting ice at 0&deg;C
a) Describe how you would use the apparatus. You may assume that ice at 0&deg;C and a stopwatch are available.

b)In an experiment, 120g of ice at 0&deg;C is to be melted. The specific latent heat of fusion of ice is 340J g^ -1. Assume that all the energy from the heater will be used to melt the ice.

c)When the experiment is carried out, the ice melts is slightly less time than the expected time.
(1)State one reason why this happen.
(2)Suggest one modification to the experiment that would reduce the difference between the experimental time and the expected time.

2.Yunnan Guoqiao-mixian is a famous Chinese food. In preparing the food, the first step is to cook a pot of chicken soup: A pot of water containing chickens is heated over a high flame until it boils. A low flame is then used to keep the soup boiling for hrs.
a) Explain why the temp. of the boiling soup remains unchanged, even though it is being heated.

b)Explain why it is undesirable to use a high flame to keep the soup boiling.

回答 (1)

天同

2009-11-05 3:50 am

✔ 最佳答案

(a) Immerse the heater into the melting ice. Swirch it on and record the time required for the ice to be completely melted.

The latent heat of fusion = heater power x time to melt the ice/mass of ice

(b) Expected time to melt the ice
= mass of ice x latnet heat of fusion/heater power
= 120 x 340/60 s
(c) (1) There is heat flow to the ice from the surroundings. Hence, the ice melted faster than expected.
(2) Use a cup of good insulation to contain the ice, so as to reduce heat absorbed from the surroundings.

2(a) The heat supplied has been absorbed by the boiling soup as latent heat. Hence, there is no temperature rise.

(b) A high flame will boil the soup away in a short time, which is not desirable for the purpose.

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