物理物態變化 DSE、CE 選擇題

1.

Questions 54 and 55 : The setup in Figure (a) is used to determine the specific latent heat of fusion of ice. At time $t=0$ , $0.15$ kg of ice cubes at $0^\circ\mathrm{C}$ are added into $1$ kg of hot water. The initial temperature of water is $60^\circ\mathrm{C}$ . Figure (b) shows the variation of the water temperature with time. At $Q$ , the mixture achieves the thermal equilibrium.

Figure (a): beaker of water with thermometer and ice cubes; Figure (b): temperature falling from 60 degrees C at P through 40 degrees C at Q towards 20 degrees C at R

What is the specific latent heat of fusion of ice estimated from this experiment ? Given : specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$

2.

Questions 54 and 55 : The setup in Figure (a) is used to determine the specific latent heat of fusion of ice. At time $t=0$ , $0.15$ kg of ice cubes at $0^\circ\mathrm{C}$ are added into $1$ kg of hot water. The initial temperature of water is $60^\circ\mathrm{C}$ . Figure (b) shows the variation of the water temperature with time. At $Q$ , the mixture achieves the thermal equilibrium.

Which of the following statements about the experiment is correct ?

3.

Three different solids, initially at $20^\circ\mathrm{C}$ , are heated at the same power.

Solid	Heat capacity / $\mathrm{J\,{}^\circ C^{-1}}$	Melting point / $^\circ$ C
$P$	300	218
$Q$	500	132
$R$	900	84

Which solid will start melting first ?

4.

Paper tray containing water heated from below by a flame

A paper tray contains some water. The tray is heated by a gentle flame from below as shown. The water in the tray starts to boil while the paper does not catch fire. Which of the following statements are correct in this situation ?

(1)Water can transfer heat away from the paper tray very quickly.

(2)Water remains at

100^\circ\mathrm{C}

when it is boiling.

(3)There is no heat transfer between the paper tray and the flame.

5.

People feel cooler when they get out of water after swimming. Which of the following is/are the reason(s) ?

(1)The water on the skin evaporates.

(2)The water on the skin absorbs latent heat of fusion.

(3)The water on the skin releases latent heat of vaporization.

6.

Figure (a): beaker of water with immersion heater on a balance; Figure (b): balance reading 0.5 kg until 2 min, then falling to 0.45 kg at 7 min

Figure (a) shows a beaker of water heated by an immersion heater. Figure (b) shows the variation of the reading of the balance with time. What is the estimated output power of the heater ? (Assume no heat lost to the surroundings.) Given : specific latent heat of vaporization of water $= 2.26\times10^6\ \mathrm{J\,kg^{-1}}$ specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$

7.

Some ice cubes at $0^\circ\mathrm{C}$ are added to $0.3$ kg of soft drink at $20^\circ\mathrm{C}$ . What is the minimum amount of ice needed to cool the soft drink to $0^\circ\mathrm{C}$ ? Given : specific heat capacity of the soft drink $= 5300\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ specific latent heat of fusion of ice $= 3.34\times10^5\ \mathrm{J\,kg^{-1}}$

8.

Temperature (degrees C) against time (s): rises from 30 to 60 degrees C in 60 s, then stays at 60 degrees C

When a certain mass of a solid substance is heated by a heater of constant power, the variation of its temperature with time is shown in the figure above. If a greater mass of the same substance is heated by the same heater, which of the following graphs best represents how its temperature varies with time ? (Assume no heat lost to the surroundings.)

9.

In an experiment, a kilowatt-hour meter is used to measure the energy supplied to an immersion heater. An electronic balance is used to measure the change of the mass. The data obtained is used to estimate the specific latent heat of vaporization of water ( $l$ ).

Polystyrene cup of water with immersion heater connected to a kilowatt-hour meter, standing on an electronic balance

If the following experimental error arises : (I) Water splashes out of the polystyrene cup as the boiling is too vigorous. (II) Water vapour condenses on the upper part of the heater and drips back into the polystyrene cup. How would the calculated value of $l$ be affected ?

	(I)	(II)
	increases	decreases
	increases	increases
	decreases	decreases
	decreases	increases

10.

Which of the following statements is/are correct ?

(1)Energy transfers from an object with higher internal energy to an object with lower internal energy.

(2)An object must absorb energy when it changes its state.

(3)Energy transfers from an object with higher temperature to an object with lower temperature.