物理 1998 年 DSE、CE 選擇題（第 2 頁）

11.

A uniform beam of length $3$ m and weight $300$ N lies on a horizontal ground. What minimum vertical force must be applied to one end of the beam to just lift that end off the ground ? (Assume the weight of the beam acts through its mid-point.)

12.

If $F$ and $F'$ are the foci of the concave lens, which of the following ray diagrams is incorrect ?

Four ray diagrams A to D for a concave lens

13.

Red and violet light entering a glass block containing a prism-shaped air cavity

A beam consisting of red and violet light travels in a glass block with an air cavity. The cavity is in the shape of a prism as shown above. Which of the following diagrams best shows the subsequent path of the beam ?

Four diagrams A to D of the emergent red and violet rays

14.

Which of the following phenomena is/are caused by the refraction of light ?

(1)If a man who is spear-fishing aims his spear at where the fish appears to be, he will miss it.

(2)A spectrum is formed when white light passes through a prism.

(3)A light ray is transmitted through a curved glass fibre.

15.

Which of the following statements about internal energy, heat and temperature is/are true ?

(1)The internal energy of a body is a measure of the total kinetic energy and potential energy of the molecules in the body.

(2)Two bodies of the same temperature always have the same amount of internal energy.

(3)Heat is a measure of the energy transferred from one body to another as a result of temperature difference between the two bodies.

16.

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 set-up is used to find the specific latent heat of fusion of ice. Which of the following is not an essential precaution to ensure an accurate result ?

17.

Temperature against time graph, rising linearly from 15 degrees C at 0 s to 25 degrees C at 60 s

The graph shows the variation of the temperature of liquid with time when the liquid is heated by a $400$ W heater. The mass of the liquid is $2$ kg. Find the specific heat capacity of the liquid. Assume all the energy given out by the heater is absorbed by the liquid.

18.

A block of melting ice with mass $0.02$ kg is put into a polystyrene cup containing $0.3$ kg of water with initial temperature $20^\circ\mathrm{C}$ . After the mixture is stirred well, the ice block melts completely and the final temperature of the water becomes $14^\circ\mathrm{C}$ . Which of the following equations can be used to find the specific latent heat of fusion of ice, $L$ ? (Given : Specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$ )

19.

Which of the following can increase the average kinetic energy of the molecules of a fixed mass of gas ?

(1)increasing the volume of the gas at constant pressure

(2)increasing the pressure of the gas at constant volume

(3)increasing the pressure of the gas at constant temperature

20.

Mechanical model of a gas: a cylinder with ball bearings under a disc, on a vibrating platform driven by a motor

The diagram shows a mechanical model of a gas. The ball bearings are set into motion by a motor-driven vibrating platform. Which of the following statements is/are correct if the operating voltage of the motor is increased ?

(1)The disc rises to a higher level.

(2)The average speed of the ball bearings increases.

(3)The average spacing between the ball bearings increases.