物理電路 DSE、CE 選擇題（第 9 頁）

81.

Arrange the following circuits in ascending order of equivalent resistances :

Three resistor networks (1), (2) and (3)

82.

Circuit with ammeters A1, A2 and A3, two resistors, a constant voltage source and a switch S

In the above circuit, $A_1$ , $A_2$ and $A_3$ are ammeters connected to a constant voltage source. What will happen to the readings of the ammeters if the switch $S$ is closed ?

$A_1$	$A_2$	$A_3$
decreases	increases	becomes zero
increases	decreases	becomes zero
no change	increases	becomes zero
no change	decreases	increases

83.

An immersion heater $A$ takes $10$ minutes to boil a kettle of water while another heater $B$ takes $40$ minutes to boil the same kettle of water under the same voltage supply. If the resistance of heater $A$ is $100\ \Omega$ , what is the resistance of heater $B$ ?

84.

A student, who wishes to find the resistance of a light bulb when connected to a certain battery, incorrectly connects a practical voltmeter and a practical ammeter as shown. What would be the most probable outcome of his error ?

Battery, ammeter in parallel with a branch containing a voltmeter in series with a light bulb

85.

Battery with ammeter A1, three identical bulbs B in parallel and ammeter A2

In the circuit shown, all bulbs $B$ are identical. If ammeter $A_1$ reads $1.8$ A, what does ammeter $A_2$ read ?

86.

24 V battery, a resistor, switches K1 and K2 each in series with a 6 ohm resistor, and a voltmeter across the parallel combination

In the circuit, when $K_1$ is closed the voltmeter reads $12$ V. What would the reading be if both $K_1$ and $K_2$ are closed ?

87.

Which of the following will increase the resistance of a metal wire ?

(1)increasing the length of the wire

(2)increasing the cross-sectional area of the wire

(3)increasing the temperature of the wire

88.

An immersion heater of resistance $50\ \Omega$ raises the temperature of $1$ kg of water by $20^\circ$ C in $3$ minutes, the voltage supply being $200$ V. What would be the energy wasted ? (Specific heat capacity of water $= 4.2\ \mathrm{kJ\,kg^{-1}\,{}^\circ C^{-1}}$ )

89.

The diagrams below show three possible arrangements of four identical resistors $R$ .

Arrangements (a), (b) and (c) of four identical resistors R between X and Y

List the arrangements in order of increasing equivalent resistance, as measured between $X$ and $Y$ .

90.

Two circuits: bulbs P and Q with a switch in series with Q, and bulbs R and S with a switch in series with S

Four identical bulbs $P$ , $Q$ , $R$ and $S$ are connected as shown in the two circuit diagrams above. What happens to the brightness of $P$ and $R$ if the switches of both circuits are closed ?

	Brightness of $P$	Brightness of $R$
	decreases	remains constant
	remains constant	decreases
	increases	remains constant
	decreases	decreases