物理 1994 年 DSE、CE 選擇題（第 3 頁）

21.

Which of the following involve(s) the application of electrostatics ?

(1)A photocopier

(2)A precipitator in the chimney of a coal-fired power station

(3)A Van de Graaff generator

22.

A student uses an ammeter and a voltmeter to find the resistance of a light bulb. He incorrectly connects the circuit as shown. Which of the following is the most probable outcome ?

6 V battery with a voltmeter in series, a light bulb in parallel with the voltmeter branch and an ammeter in parallel

23.

6 V battery with a 4 ohm resistor in series with two 4 ohm resistors in parallel between X and Y

Find the p.d. between $X$ and $Y$ in the above circuit.

24.

Battery with switch S in parallel with bulb L1, bulb L2 and bulb L3

In the above circuit, all the light bulbs are identical. What happens to the brightness of the bulbs $L_1$ , $L_2$ and $L_3$ if switch $S$ is closed ?

$L_1$	$L_2$	$L_3$
decreases	increases	remains unchanged
increases	remains unchanged	increases
decreases	remains unchanged	remains unchanged
remains unchanged	decreases	increases

25.

Which of the following diagrams correctly shows the connection of the wires of an iron to the pins of a plug ? ( $L$ : Live, $N$ : Neutral, $E$ : Earth)

Four diagrams A to D showing different connections of the live, neutral and earth pins to an iron through a switch

26.

Label: operating voltage 220 V / 50 Hz, power 500 W

The diagram shows the label attached to a rice cooker. Which of the following statements is/are true when the cooker is working at its rated values ?

(1)The resistance of the cooker is

96.8\ \Omega

.

(2)The cooker draws a current of

4.4

A from the mains supply.

(3)The cooker consumes

1

kWh of electrical energy in

2

hours.

27.

Which of the following statements about direct current (d.c.) and alternating current (a.c.) is/are correct ?

(1)All d.c. sources produce constant voltages.

(2)The direction of current in an a.c. circuit changes with time.

(3)Both d.c. and a.c. produce a heating effect in a resistor.

28.

Which of the following correctly shows the major energy change in the device when it is working ?

Device	From	To
A microphone	electrical	sound
A loudspeaker	sound	electrical
A dynamo	electrical	electrical
A motor	electrical	mechanical

29.

The diagram shows three long straight wires $X$ , $Y$ and $Z$ . $X$ and $Y$ carry currents flowing into the paper while $Z$ carries a current flowing out of the paper. The currents are all equal in magnitude. What is the direction of the resultant force acting on $X$ ?

Wires Z (out of paper), X and Y (into paper) with four directions P, Q, R and S marked at X

30.

An electrical power of $100$ kW is transmitted at $20$ kV through cables of total resistance of $4\ \Omega$ . Find the voltage drop and power loss in the cables.

	Voltage drop	Power loss
	$20$ V	$20$ W
	$20$ V	$100$ W
	$100$ V	$20$ W
	$100$ V	$100$ W