物理 2004 年 DSE、CE 選擇題（第 4 頁）

31.

6 V battery with resistor X; 12 V battery with resistors Y and Z in parallel

In the above circuits, $X$ , $Y$ and $Z$ are identical resistors. The power dissipated in $X$ is $20$ W. Find the total power dissipated in $Y$ and $Z$ .

32.

One day, Donald used the following electrical appliances at home :

Appliance	Rating	Duration	Cost of electricity
electric heater	$220$ V, $2500$ W	$30$ minutes	$C_1$
television	$220$ V, $270$ W	$5$ hours	$C_2$
lamp	$220$ V, $150$ W	$8$ hours	$C_3$

Which of the following relationships is correct ?

33.

Wires P and Q carrying currents into the paper and a point R equidistant from both

Two parallel straight wires $P$ and $Q$ carry equal currents flowing into the paper. A compass is placed at a point $R$ where $PR = QR$ . In which of the following diagrams is the north pole of the compass needle pointing in the correct direction ? The effect of the Earth's magnetic field may be ignored.

Options A to D: compass needle pointing left, right, up, down

34.

Rectangular coil at position A moving to position B across a uniform magnetic field pointing into the paper

A rectangular coil is moved with a uniform speed from position $A$ to position $B$ as shown above. Which of the following graphs represents the variation of the current induced in the coil with time ?

35.

Generator: coil rotating between two magnet poles with slip rings, brushes and a load PQ

The diagram shows a generator connected to a load. Which of the following statements is/are correct ?

(1)The generator produces an alternating current through the load.

(2)At the instant shown, a current is flowing through the load from

P

to

Q

.

(3)The current produced reaches a maximum when the coil is vertical.

36.

Photographs of a sine-wave trace on a CRO and of the voltage gain and time-base settings

The photographs show the trace of a signal on a CRO and some settings of the CRO. The voltage gain is set at $0.5$ V per cm and the time-base is set at $10$ ms per cm. Find the frequency and peak voltage of the input signal.

	Frequency / Hz	Peak Voltage / V
	$10$	$2$
	$10$	$4$
	$20$	$2$
	$20$	$4$

37.

${}^{2}_{1}\mathrm{H}+{}^{x}_{1}\mathrm{H}\to{}^{4}_{y}Z+\text{a neutron}$ Find the values of $x$ and $y$ in the above nuclear reaction.

	$x$	$y$
	$2$	$1$
	$2$	$2$
	$3$	$1$
	$3$	$2$

38.

Different absorbers are placed in turn between a radioactive source and a Geiger-Muller tube. Three readings are taken for each absorber. The following data are obtained :

Absorber	Count rate / $\mathrm{s^{-1}}$
–	200	205	198
Paper	197	202	206
5 mm aluminium	112	108	111
25 mm lead	60	62	58
50 mm lead	34	36	34

What type(s) of radiation does the source emit ?

39.

In order to detect cracks in an underground oil pipe, an engineer proposes adding a radioactive source to the oil. Which of the following sources is most suitable ?