物理 2010 年 DSE、CE 選擇題（第 2 頁）

11.

Figure (a): beaker of water with immersion heater on a balance; Figure (b): balance reading 0.5 kg until 2 min, then falling to 0.45 kg at 7 min

Figure (a) shows a beaker of water heated by an immersion heater. Figure (b) shows the variation of the reading of the balance with time. What is the estimated output power of the heater ? (Assume no heat lost to the surroundings.) Given : specific latent heat of vaporization of water $= 2.26\times10^6\ \mathrm{J\,kg^{-1}}$ specific heat capacity of water $= 4200\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}$

12.

In the figure, a firecracker at a position $80$ m away from a building explodes and produces a bang. A girl standing $90$ m away from the firecracker hears two bangs. What is the time interval between the two bangs ? Given : speed of sound in air $= 340\ \mathrm{m\,s^{-1}}$

Building, firecracker 80 m from the building and a girl 90 m from the firecracker

13.

A student performs an experiment to find the refractive index of a material and the result is shown below. Which of the following set of data is likely to be wrong ?

	$P$	$Q$	$R$	$S$
Angle of incidence	$20^\circ$	$40^\circ$	$60^\circ$	$80^\circ$
Angle of refraction	$14^\circ$	$22^\circ$	$38^\circ$	$44^\circ$

14.

Two parallel rays X and Y meeting at P after passing through lens L; ray Z parallel to the principal axis; points Q, R, S on the axis

Two parallel rays $X$ and $Y$ meet at $P$ after passing through lens $L$ as shown. Another ray $Z$ parallel to the principal axis is directed to lens $L$ . Which point in the figure will ray $Z$ pass through ?

15.

Which of the following statements about sound waves is **not** correct ?

16.

The photo below shows the back of a microwave oven.

Photograph of the back of a microwave oven with label: power supply 220 V - 50 Hz, power consumption 1150 W, microwave output 750 W, microwave frequency 2450 MHz

Which of the following statements is/are correct ?

(1)The current flowing through the microwave oven is about

3.4

A.

(2)Around

65\%

of electrical energy is converted into energy carried by microwave.

(3)The wavelength of the microwave emitted is about

0.12

m.

17.

A car has two doors and an indicator lamp is installed to act as a car door warning signal. When either or both doors are open, the lamp lights up. A student designs four different circuits for this application. A switch is installed in each door. The switch is open when the car door opens. Which of the following circuits is correct ?

Four circuits A to D with a battery, resistor, lamp and two door switches

18.

1.5 V cell with a switch and a light bulb in series, voltmeter P across the switch and voltmeter Q across the bulb

In the circuit above, voltmeters $P$ and $Q$ of very high resistance are connected across the switch and the light bulb respectively. What are the voltmeter readings when the switch is open ?

	reading of $P$ / V	reading of $Q$ / V
	$0$	$0$
	$0$	$1.5$
	$1.5$	$0$
	$1.5$	$1.5$

19.

Circuit with 9 V battery, two resistors R in parallel, in series with a bulb

In the circuit above, the rating of the bulb is " $6$ V, $12$ W". Find the resistance of $R$ so that the bulb will work at its rated value.

20.

Electric kettle with live, neutral (with switch S and fuse) and earth wires, point P and metal case

In the figure above, the kettle is wired incorrectly. Which of the following statements is correct when point $P$ is accidentally connected to the metal case ?