物理 2000 年 DSE、CE 選擇題（第 3 頁）

21.

Battery with a 4 ohm resistor in series with R1 = 6 ohm and R2 = 12 ohm in parallel between P and Q

Three resistors are connected to a battery as shown above. Which of the following statements is/are correct ?

(1)The current passing through

R_1

is equal to that passing through

R_2

.

(2)The voltage across

R_1

is equal to that across

R_2

.

(3)The energy dissipated by one coulomb of charge passing through the

4\ \Omega

-resistor is equal to that dissipated by one coulomb of charge passing through

PQ

.

22.

Battery with resistors R1, R2, R3 in parallel branches with ammeters A1, A2, A3 and a switch S in the R3 branch

If switch $S$ in the above circuit is closed, which of the following statements is/are correct ?

(1)The readings of ammeters

A_1

and

A_2

are both increased.

(2)The ratio of the readings of ammeters

A_1

and

A_2

is increased.

(3)The reading of ammeter

A_3

remains unchanged.

23.

9 V battery with an ammeter, a resistor and a bulb in parallel

A resistor and a bulb are connected in parallel to a $9$ V battery as shown above. The reading of the ammeter is $5$ A. If the power dissipated by the resistor is $18$ W, find the power dissipated by the bulb.

24.

Electric iron with heating element, contact points X and Y, switch, fuse, metal case and earth connection

The above diagram shows the main parts of an electric iron. In which of the following situations will the fuse blow when the switch is closed ?

(1)The insulation at contact point

X

is worn out so that the wire touches the metal case.

(2)The insulation at contact point

Y

is worn out so that the wire touches the metal case.

(3)The heating element is broken.

25.

Experimental set-up with battery, variable resistor, switch, bulb, ammeter and voltmeter with wires (1), (2), (3) and terminals P, Q, R

The above figure shows an experimental set-up for measuring the resistance of a bulb. To which of the terminals $P$ , $Q$ and $R$ should each of the wires be connected ?

Wire (1)	Wire (2)	Wire (3)
$P$	$Q$	$R$
$P$	$R$	$Q$
$Q$	$P$	$R$
$R$	$P$	$Q$

26.

A bar magnet is placed near a solenoid. Which of the following correctly shows the direction of the induced current in the solenoid ? (Note : The arrow " $\rightarrow$ " indicates the direction of motion of the magnet or solenoid.)

Four diagrams A to D of a bar magnet and a solenoid connected to a galvanometer, with motion arrows and induced current directions

27.

Which of the following statements about $\alpha$ particles and $\gamma$ rays is correct ?

28.

Which one of the following is not a safety precaution for handling radioactive sources ?