物理 2010 年 DSE、CE 選擇題（第 4 頁）

31.

The figure shows the temperature-time graph of two objects $X$ and $Y$ when they are heated at the same power. Which of the following deductions are correct ?

(1)The heat capacity of

X

is smaller.

(2)If

X

and

Y

are made of the same material, the mass of

X

is smaller.

(3)The specific heat capacity of

X

is smaller.

Temperature against time lines for X (steeper) and Y, both starting from the same point

32.

Transverse wave on a string travelling to the left, with particle P on the equilibrium position

A wave travels along a string to the left. The figure above shows its waveform at time $t=1$ s. Which of the following displacement-time graphs best represents the motion of particle $P$ ? (Take displacement upwards to be positive.)

33.

Figure (a) shows the equilibrium positions of particles $E$ to $N$ in a medium. A longitudinal wave is travelling from left to right. At time $t_1$ , the positions of the particles are shown in Figure (b).

Figure (a): equilibrium positions of particles E to N. Figure (b): positions at time t1

Which of the following particles is momentarily at rest at $t_1$ ?

34.

Two point sources $S_1$ and $S_2$ are producing circular water waves in a ripple tank. The figure shows the wave pattern at a certain instant. Solid lines represent crests and dotted lines represent troughs. Which of the following statements is/are correct ?

(1)The water particle at

A

is always at rest.

(2)The water particle at

B

is always at a crest.

(3)The interference at

C

is neither constructive nor destructive.

Circular wavefronts (solid for crests, dotted for troughs) from S1 and S2 with points A, B and C marked

35.

Stationary laser speed gun emitting laser pulses towards an approaching car

In the figure, a laser speed gun is used to check for speeding. A car is approaching the speed gun. The speed gun emits a laser pulse. The speed gun receives the reflected pulse from the car after $3.6\times10^{-7}$ s. After $0.2$ s, the speed gun emits another laser pulse. The speed gun receives the reflected pulse from the car after $3.1\times10^{-7}$ s. What is the estimated speed of the car ? Given that speed of the laser pulse is $3\times10^{8}\ \mathrm{m\,s^{-1}}$ .

36.

A ray of light enters a transparent rectangular block and travels along the path as shown in the figure above. Find angle $\theta$ .

Ray entering a rectangular block at angle theta to the left face and leaving along the top at 40 degrees

37.

A sound wave travelling in water towards the water-air boundary

The figure shows a sound wave travelling in water. It is known that the sound waves travel faster in water than in air. After refraction, which of the following statements is/are correct ?

(1)The wavelength of the sound wave increases.

(2)The frequency of the sound wave remains unchanged.

(3)The sound wave bends away from the normal.

38.

Two loudspeakers connected in parallel to a signal generator; points O, P, Q and a sound intensity level meter moved from P to Q

Two identical loudspeakers are connected in parallel to a signal generator, $O$ is the midpoint between the loudspeakers. When a sound intensity level meter is moved from $P$ to $Q$ , the graph below shows the variation of the sound intensity level received with position.

Graph of sound intensity level against position, decreasing from P to Q

Which of the following statements is/are correct ?

(1)The sound intensity level at

Q

is smaller because the amplitude of the sound wave decreases as it is further away from the loudspeakers.

(2)Constructive interference occurs at point

P

while destructive interference occurs at point

Q

.

(3)The result of the experiment shows that sound is a wave.

39.

Resistor network PQRS with 3 ohm, 2 ohm and 1 ohm resistors, battery and ammeter, with wires X and Y to be connected

In the circuit shown, wires $X$ and $Y$ are to be connected to two points in the resistor network $PQRS$ . Across which two points should $X$ and $Y$ be connected so that the ammeter reading will be a minimum ?

40.

Copper ring R above a solenoid carrying current I; points X (above the solenoid) and Y (centre of the solenoid); observer at O above

A copper ring $R$ is falling through a solenoid along the axis as shown. The plane of the ring is kept horizontal throughout. The solenoid is carrying a steady current $I$ . $Y$ is the centre of the solenoid. Which of the following combinations about the directions of the induced current in the ring (if any) at $X$ and at $Y$ as observed from $O$ is correct ?

	at $X$	at $Y$
	clockwise	clockwise
	clockwise	no current
	anticlockwise	clockwise
	anticlockwise	no current