物理 2006 年 DSE、CE 選擇題（第 3 頁）

21.

Kilowatt-hour meter label: 220 V, 50 Hz, circular disc, 600 revolutions / kWh

The figure shows the label of a kilowatt-hour meter connected to a mains supply. When an appliance is switched on for $2$ minutes, the circular disc rotates through $24$ complete revolutions. What is the electric power consumed by the appliance ?

22.

A rubbed plastic ruler can attract paper scraps before actually touching them. Which of the following descriptions about the charges on the rubbed ruler and the original charges on the paper scraps are possible ?

(1)The ruler and the paper scraps carry opposite charges.

(2)Both the ruler and the paper scraps are uncharged.

(3)The ruler carries charges and the paper scraps are uncharged.

23.

Simple circuit with a resistor and a cell, point X marked on the wire

If the current in the circuit shown is $0.8$ A, what is the number of electrons passing the point $X$ in $1$ minute ?

24.

Cell with bulb X in series with bulbs Z and Y in parallel

Three identical light bulbs are connected to a cell as shown in the diagram. After some time, the filament of bulb $Z$ breaks. What will happen to the brightness of the remaining light bulbs ?

	Brightness of $X$	Brightness of $Y$
	increases	increases
	increases	decreases
	decreases	increases
	decreases	decreases

25.

Some fresh foods are exposed to $\gamma$ radiations from radioactive isotopes for a short time so that the micro-organisms in the foods can be killed. Why are the irradiated foods not harmful to people who eat them ?

26.

A car travels along a straight road from $A$ to $B$ with a uniform acceleration. The speed of the car is $v_1$ at the instant when half of the journey time from $A$ to $B$ is elapsed and its speed is $v_2$ at the mid-way of $A$ and $B$ . Which of the following is correct ?

27.

Acrobat standing in the middle of a cable between two posts, the cable making angle theta with each post

An acrobat is standing in the middle of a cable as shown. The angle $\theta$ is less than $60^\circ$ . Which of the following relations between the tension $T$ of the cable and the weight $W$ of the acrobat is correct ? (Neglect the weight of the cable.)

28.

A bow is pulled horizontally to create a tension of $50$ N on its string as shown in the figure. What is the net horizontal force acting on the arrow when it is released ?

A bow whose string, under 50 N tension on each side, makes 40 degrees with the arrow on each side

29.

A student performed an experiment to investigate the factors affecting the acceleration of a trolley carrying different loads. The table below shows the data recorded :

Trial	Net Force / N	Total mass of the loaded trolley / kg	Acceleration / $\mathrm{m\,s^{-2}}$
(i)	2	2	1
(ii)	2	1	2
(iii)	2	0.5	4
(iv)	4	2	2
(v)	4	4	1
(vi)	8	2	4

Which trials can the student use to deduce the relationship between the acceleration and the net force acting on the trolley ?

30.

A light ray enters normally into a right-angled prism and is totally internally reflected at face $AB$ as shown below. Based on this optical phenomenon, which of the following is/are the possible value(s) for the refractive index of the material of the prism ?

(1)

1.35

(2)

1.45

(3)

1.55

Ray entering a right-angled prism normally and reflected at face AB with a 45 degree angle at A