物理電路 DSE、CE 選擇題（第 4 頁）

31.

A square loop $PQRS$ is made of uniform resistance wire. Let $X$ , $Y$ and $Z$ be the equivalent resistance of the loop when connected as shown below :

Table of three ways of connecting a square loop PQRS, with equivalent resistances X, Y and Z

Which of the following relations is correct ?

32.

Figure (a): circuit with cell, ammeter, resistance wire, variable resistor and voltmeter. Figure (b): straight V against I graph

Figure (a) shows a circuit used to investigate how the voltage $V$ across a resistance wire varies with the current $I$ through the wire. The result is shown in Figure (b). If the experiment is repeated using a thinner wire of the same material and of equal length, which of the following graphs (denoted by the dashed line) represents the expected result ?

Four V against I graphs A to D, each with a solid line and a dashed line

33.

In the circuit shown, both ammeters $A_1$ and $A_2$ read $1$ A when the switch $S$ is open. Find the readings of the two ammeters when $S$ is closed.

Battery, 3 ohm resistor with ammeter A1, and 6 ohm resistor with switch S in parallel, with ammeter A2 in the main line

	$A_1$	$A_2$
	$0.5$ A	$1.5$ A
	$0.67$ A	$1$ A
	$1$ A	$1.5$ A
	$1$ A	$3$ A

34.

V against I graph with two straight lines X and Y from the origin, Y steeper; regions P (above Y) and Q (below X)

The figure above shows the voltage-current ( $V$ - $I$ ) graphs of two resistors $X$ and $Y$ . Which of the following deductions is/are correct ?

(1)The resistance of

X

is higher than that of

Y

.

(2)If

X

and

Y

are connected in series, the

V

-

I

graph of the combined resistor will lie in region

P

.

(3)If

X

and

Y

are connected in parallel, the

V

-

I

graph of the combined resistor will lie in region

Q

.

35.

Which of the following relations is incorrect ?

36.

If the ammeter in the circuit reads $3$ A, find the voltage of the battery.

Battery with 2 ohm and 1 ohm resistors in parallel, in series with a 3 ohm resistor and an ammeter

37.

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

.

38.

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.

39.

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.

40.

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)
$P$	$Q$	$R$
$P$	$R$	$Q$
$Q$	$P$	$R$
$R$	$P$	$Q$