物理物態變化 DSE、CE 選擇題（第 2 頁）

11.

Which of the following has the highest average speed of the molecules ?

12.

Water has a very high value of specific latent heat of vaporization. Which of the following statements can be illustrated by this fact ?

(1)Water is used as the coolant in car engines.

(2)Coastal region has milder climate as comparing with inland region.

(3)Steam at

100^\circ\mathrm{C}

causes more serious injury to skin than boiling water.

13.

In an experiment, $2$ kg of water at $20^\circ\mathrm{C}$ is heated inside a boiler for $20$ minutes. Water is boiled to $100^\circ\mathrm{C}$ and $1.7$ kg of water remains after boiling. What is the estimated power of the boiler ? Given : Specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ Specific latent heat of vaporization $= 2.26\times10^6\ \mathrm{J\,kg^{-1}}$

Boiler containing water with a heater connected to the mains supply

14.

Which of the following statements about evaporation are correct ?

(1)Evaporation occurs only on the surface of the liquid.

(2)The rate of evaporation is higher when the temperature is higher.

(3)After evaporation, the average kinetic energy of the remaining liquid molecules will increase.

15.

A space shuttle is covered by 'heat shields' over its body so as to protect the interior from getting too hot while entering the atmosphere of the Earth. Which of the following thermal properties is/are desirable for the material of the 'heat shields' ?

(1)It should be a good conductor of heat.

(2)It should have a very high melting point.

(3)It should have high specific heat capacity.

16.

A substance $X$ is heated at a constant rate and its changing temperature over a time period is recorded. The data are plotted below.

Temperature (degrees C) against time: rises from -20 with a flat section at -20, crosses 0, rises to 80, flat at 80, then rises again

Which of the following statements about the substance $X$ is incorrect ?

17.

The initial temperature of a jar of juice is $80^\circ\mathrm{C}$ and the mass of the juice is $2$ kg. Susan adds ice cubes into the jar in order to cool down the juice to $20^\circ\mathrm{C}$ . What is the minimum number of ice cubes at $0^\circ\mathrm{C}$ required ? (Neglect the heat capacity of the jar and assume there is no heat exchange with the surroundings.) Given : Mass of each ice cube $= 0.15$ kg Specific heat capacity of juice $= 4700\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ Specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ Specific latent heat of fusion of ice $= 3.34\times10^5\ \mathrm{J\,kg^{-1}}$

18.

Figure (a): misty glasses; Figure (b): clear glasses

When Joanne gets off from an air-conditioned bus in the summer, her glasses become misty (see Figure (a)). After a while, the glasses become clear again (see Figure (b)). Which of the following physical processes are involved in the above phenomenon ?

19.

If equal masses of boiling water and melting ice cubes are mixed, which of the following best describes the state of the mixture ? (Specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ ; Specific latent heat of fusion of ice $= 3.34\times10^5\ \mathrm{J\,kg^{-1}}$ )

20.

Temperature against time for substances P and Q heated separately from room temperature, each with a flat section

The graph shows the variation in temperature of equal masses of two substances $P$ and $Q$ when they are separately heated by identical heaters. Which of the following deductions is correct ?