物理 2008 年 DSE、CE 選擇題（第 2 頁）

11.

Light bulb O, lens L and screen S on a line

A light bulb $O$ is placed in front of a lens $L$ as shown above. A sharp and diminished image is formed on the screen $S$ . With the position of $L$ fixed, which of the following methods can form a sharp and magnified image on the screen ?

12.

Plane mirror MN on a wall, observer E 1 m from the wall and 1.5 m above ground, and a 3 m post PQ 4 m behind the observer

In the figure, a plane mirror $MN$ of height $h$ is mounted in an adjustable vertical position on a vertical wall. $E$ is an observer's eye which is $1$ m from the wall and $1.5$ m above the ground. $PQ$ is a vertical post of height $3$ m and is $4$ m behind the observer. Looking into the mirror the observer can see the whole image of the post. What is the minimum value of $h$ ?

13.

A ship uses a sonar system to detect the depth of the sea. A sound wave signal of frequency $30000$ Hz is sent vertically downward from the sea surface and the reflected signal is received $5$ s later. Which of the following is correct ? (The speed of sound wave in sea water is $1400\ \mathrm{m\,s^{-1}}$ .)

	Wavelength of the sound wave in sea water (m)	Depth of the sea (m)
	$4.67\times10^{-2}$	3500
	$4.67\times10^{-2}$	7000
	$9.33\times10^{-2}$	3500
	$9.33\times10^{-2}$	7000

14.

Which of the following ray diagrams concerning the refraction of two light rays by a converging lens is/are possible ?

Three ray diagrams (1), (2), (3) for a converging lens

15.

A light ray undergoes reflection and refraction at an air-glass boundary as shown. $PQ$ is perpendicular to $RS$ . $OX$ , $OY$ and $OZ$ are the paths of the light rays. Which of the following deductions is/are correct ?

(1)

OX

is the path of the incident ray.

(2)

RS

is the air-glass boundary.

(3)The light ray travels from glass to air.

Rays OX, OY and OZ at the point O on line RS, with PQ perpendicular to RS; angles 60, 40 and 60 degrees marked

16.

A ray of light is traveling from glass to air as shown in the figure. Which of the following ratios is the refractive index of glass ?

Ray from glass to air making angle theta with the boundary in glass and angle phi with the boundary in air

17.

Table of three ways of connecting a circular loop, with equivalent resistances X, Y and Z

A circular loop is made of uniform resistance wire. Let $X$ , $Y$ and $Z$ be the equivalent resistance of the loop when connected as shown above. Which of the following is correct ?

18.

Two parallel wires each carrying current I in the same direction

Two parallel wires carry equal currents flowing in the same direction. Which of the following statements are correct ?

(1)The magnetic forces acting on the two wires form an action-reaction pair.

(2)The two wires attract each other.

(3)If the directions of the current in the two wires are both reversed, the wires will repel each other.

19.

4 V battery in series with bulbs A and B

The figure shows two light bulbs $A$ and $B$ , which are connected in series. The voltages across $A$ and $B$ are $3$ V and $1$ V respectively. Which of the following statements is/are correct ?

(1)The resistance of

A

is greater than that of

B

.

(2)The current flowing through

A

is greater than that through

B

.

(3)

A

is dimmer than

B

.

20.

Battery V with a 12 ohm resistor in series with two 6 ohm resistors in parallel, an ammeter in one branch

In the above circuit, the reading of the ammeter is $0.3$ A. What is the voltage $V$ of the battery ?