物理 1985 年 DSE、CE 選擇題（第 2 頁）

11.

Heat is needed to keep water boiling because energy is required to

(1)increase the potential energy of the water molecules.

(2)increase the kinetic energy of the water molecules.

(3)increase the average speed of the water molecules.

12.

The difference in water temperature between the top and the bottom of a waterfall is $0.15^\circ\mathrm{C}$ . Assuming no heat is lost from the water to the surroundings, what is the height of the waterfall ? (The specific heat capacity of water is $4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ .)

13.

Object O and its upright image I on the same side, with points A, B, C and D on the axis

In the above figure, the image $I$ of an object placed at $O$ is produced by a single lens. If the magnification is $2$ , what kind of lens has been used and where must it have been placed ?

14.

In the diagram shown, a light ray passes from medium $Y$ to medium $X$ and emerges to medium $Y$ again. The refractive index of medium $X$ is smaller than that of medium $Y$ . Which of the following represents the path of the emergent ray ?

Ray passing from medium Y through a slab of medium X back into medium Y, with possible emergent rays P, Q, R and S

15.

Which of the following are longitudinal waves ?

(1)sound waves transmitted through a solid

(2)sound waves transmitted through water

(3)waves in a vibrating string

16.

When light travels from air to glass, which of the following statements is/are true ?

(1)The speed of the light changes.

(2)The wavelength of the light increases.

(3)The frequency of the light remains unchanged.

17.

A short pulse of microwave travelling at $3\times10^{8}\ \mathrm{m\,s^{-1}}$ was used to detect the position of a stationary weather balloon. It was found that the microwaves reflected from the balloon were picked up $2\times10^{-4}$ s after the pulse had been emitted from the station. The distance of the balloon from the station was

18.

Which of the following is in the correct order of increasing wavelengths ?

19.

A stationary wave is produced in a string by a vertical vibrator as shown in the diagram. If $P$ is the crest of an antinode, what is the direction of motion of the point $A$ at that instant ?

Stationary wave on a string between a vibrator and a wall, P at a crest and A just to the right of P

20.

Two uncharged metal spheres on insulating threads separated by a plastic sheet, positively charged rod X nearby

Two uncharged metal spheres are suspended by insulating threads as shown in the diagram. A plastic sheet is put between them. When a positively charged rod $X$ is brought near them as shown, which of the following diagrams shows the resulting charge distribution of the spheres ?

Four diagrams A to D of charge distributions on the two spheres separated by a plastic sheet