物理物態變化 DSE、CE 選擇題（第 4 頁）

31.

Questions 22 and 23 : The following apparatus is used to find the specific latent heat of vaporization of a liquid.

Beaker of liquid with immersion heater connected to a power supply, standing on an electronic balance

When the liquid boils, the reading of the balance is taken. After $200$ s, the reading of the balance decreases by $0.02$ kg. The power output of the heater is $150$ W. If $20\%$ of the energy supplied is lost to the surroundings, find the specific latent heat of vaporization of the liquid.

32.

Questions 22 and 23 : The following apparatus is used to find the specific latent heat of vaporization of a liquid.

Which of the following can improve the accuracy of the experiment ?

(1)covering the beaker with a lid

(2)completely immersing the heating coil in liquid

(3)stirring the liquid throughout the experiment

33.

Temperature against time graphs for solids X and Y: X rises steeply with a short flat section, Y rises less steeply with a longer flat section at higher temperature

Two solids $X$ and $Y$ of equal mass are separately heated by two identical heaters. The above figure shows the variation of the temperatures of the substances with time. Which of the following statements is/are correct ?

(1)The melting point of

X

is higher than that of

Y

.

(2)The specific heat capacity of

X

is smaller than that of

Y

.

(3)The specific latent heat of fusion of

X

is smaller than that of

Y

.

34.

Which of the following substances is a liquid at room temperature (about $20^\circ\mathrm{C}$ ) ?

Substance	Melting point / $^\circ$ C	Boiling point / $^\circ$ C
$P$	25	444
$Q$	$-39$	357
$R$	44	280
$S$	$-218$	$-183$

35.

The melting point of copper is $1080^\circ\mathrm{C}$ and its specific latent heat of fusion is $2.1\times10^5\ \mathrm{J\,kg^{-1}}$ . How much energy is needed to melt $0.5$ kg of copper at its melting point ?

36.

Two identical set-ups with ice in funnel X (heater connected to power supply) and funnel Y (heater not connected), each with a beaker below

The above apparatus is used to find the specific latent heat of fusion of ice. Which of the following is an essential precaution to ensure an accurate result ?

37.

An immersion heater is used to heat a cup of water. It takes $10$ minutes to bring the water from $20^\circ\mathrm{C}$ to its boiling point $100^\circ\mathrm{C}$ . Find the time taken for the heater to vaporize the boiling water completely. (Given : specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ specific latent heat of vaporization of water $= 2.268\times10^6\ \mathrm{J\,kg^{-1}}$ .)

38.

Temperature against time graph on a grid, time axis marked 0, 200, 400, 600 s, with a flat section

A $400$ W electric heater is used to heat $0.4$ kg of a solid. The graph shows the temperature against time of the substance. The specific latent heat of fusion of the substance is

39.

The apparatus shown is used to find the specific latent heat of vaporization of water. Which of the following is NOT correct ?

Beaker of water with immersion heater connected to joulemeter and power supply, standing on an electronic balance

40.

Graph of temperature against time for a solid heated by a 20 W heater: rising, then a flat melting section, then rising again

A $20$ W heater is used to melt a solid. A graph of temperature $\theta$ against time $t$ is plotted as shown above. If a heater of $40$ W is used, which graph (using the same scale) would be obtained ?