物理波的現象 DSE、CE 選擇題（第 4 頁）

31.

A vibrator generates a stationary wave on a string. The diagram shows the string at an instant of maximum displacement. Which of the following statement is correct ?

Stationary wave on a string between a vibrator and a fixed end, with particles P, Q, R and S marked

32.

Plane water waves travelling upwards towards a straight barrier PQ inclined to the waves

Plane water waves travel towards a straight barrier $PQ$ as shown in the figure above. Which of the following diagrams best shows the reflected waves ?

33.

Two vibrators P and Q in a ripple tank, N the midpoint of PQ and M on the perpendicular bisector MN

Two vibrators $P$ and $Q$ are set to vibrate in phase in a ripple tank. $MN$ is the perpendicular bisector of $PQ$ as shown above. Which of the following statements is/are true ?

(1)Constructive interference occurs along

MN

.

(2)Destructive interference occurs along

PQ

.

(3)A crest is always formed at

M

.

34.

In a ripple tank experiment, the pattern of plane water waves is frozen by using a stroboscopic lamp flashing at a frequency of $50$ Hz as shown in the above diagram. If the frequency of the vibrator is $50$ Hz, find the wavelength and speed of the waves.

Frozen pattern of plane water waves with four wavelengths spanning 20 cm

	Wavelength	Speed
	$4$ cm	$2\ \mathrm{m\,s^{-1}}$
	$4$ cm	$12.5\ \mathrm{m\,s^{-1}}$
	$5$ cm	$2.5\ \mathrm{m\,s^{-1}}$
	$5$ cm	$10\ \mathrm{m\,s^{-1}}$

35.

Source S, double slits P and Q, and a point M with PM = 53 cm and QM = 50 cm

In a double-slit experiment, a source $S$ sends waves towards two slits $P$ and $Q$ , which are equidistant from $S$ . The distances of a point $M$ from $P$ and $Q$ are $53$ cm and $50$ cm respectively. If constructive interference occurs at $M$ , the possible wavelength of the waves is

36.

Plane waves in a shallow region approaching a barrier with a small slit, deep region beyond

The figure above shows a series of plane water waves travelling in a shallow region of water. The waves pass through a small slit to a deep region of water. Which of the following diagrams shows the wave pattern in the deep region ?

Four wave patterns A to D beyond the slit

37.

Plane water waves travelling to the right towards an obstacle

A series of water waves, generated in water of uniform depth, is travelling towards an obstacle as shown above. Which of the following diagrams best shows the wave pattern after passing the obstacle ?

Four wave patterns A to D after the obstacle

38.

Straight barrier PQ with a pulse AB travelling towards it at 30 degrees to the barrier

A straight pulse $AB$ is travelling towards a straight barrier $PQ$ in a ripple tank as shown above. Which of the following figures best shows the reflected pulse ?

Four figures A to D showing a reflected pulse at different angles

39.

In a ripple tank experiment, a series of plane water waves passes through a narrow slit. Which of the following properties of the waves will remain unchanged ?

(1)speed

(2)direction of travel

(3)frequency

40.

Circular wave pattern from coherent point sources S1 and S2 with points X, Y and Z marked

The figure above shows the wave pattern in a ripple tank from coherent point sources $S_1$ and $S_2$ . What kind of interference occurs at $X$ , $Y$ and $Z$ ?

$X$	$Y$	$Z$
destructive	constructive	constructive
no interference	constructive	constructive
no interference	destructive	no interference
no interference	destructive	constructive