物理 1988 年 DSE、CE 選擇題（第 2 頁）

11.

In the circuit shown, the energy required by an electron to travel from $Q$ to $P$ through $X$ is $E_1$ and that through $Y$ is $E_2$ . Which of the following is correct ?

Resistor X (2 ohm) and resistor Y (4 ohm) in parallel between P and Q, connected to a battery

12.

What should be the potential difference between $P$ and $Q$ in the circuit shown ?

12 V battery with 1 ohm and 3 ohm resistors in series and a voltmeter, points P and Q marked

13.

In the circuit shown, which of the switches should be closed in order to get the maximum brightness in lamp $L$ ?

Battery with three lamps in series including L and switches X, Y and Z

14.

Electron path entering the dashed square region PQRS and bending downwards

The figure shows the path of an electron in a magnetic field $PQRS$ . What should be the direction of the magnetic field ?

15.

A 3-pin plug is connected to a boiler of rating " $2000$ W, $200$ V". Which of the following statements is/are true ?

(1)A

5

A fuse should be used in the circuit.

(2)The fuse should be placed on the brown wire of the cable.

(3)The yellow and green wire of the cable should be connected to the earth pin.

16.

The atomic number of Tin is $50$ and its mass number is $112$ . Which of the following is an isotope of Tin ?

17.

The activity of a radioactive source falls to $\frac{1}{8}$ of its original value in $24$ minutes. The half-life of the source is

18.

A U-235 nucleus would change to Ac-227 through a series of decay : ${}^{235}_{92}\mathrm{U}\xrightarrow{X}{}^{231}_{90}\mathrm{Th}\xrightarrow{Y}{}^{231}_{91}\mathrm{Pa}\xrightarrow{Z}{}^{227}_{89}\mathrm{Ac}$ What kind of particles are emitted at stages $X$ , $Y$ and $Z$ in the radioactive decay chain shown above ?

$X$	$Y$	$Z$
$\alpha$	$\alpha$	$\beta$
$\beta$	$\alpha$	$\beta$
$\beta$	$\beta$	$\alpha$
$\alpha$	$\beta$	$\alpha$