物理 1981 年 DSE、CE 選擇題（第 2 頁）

11.

Which of the following statements is/are correct ?

(1)Sound waves cannot be diffracted.

(2)A louder sound travels faster in air.

(3)Sound travels faster in water than in air.

12.

Given the following types of electromagnetic waves :

(1)radio waves

(2)yellow light

(3)green light

The waves listed in ascending order of their wavelengths are :

13.

Suppose that it takes $8$ minutes to boil a kettle of water. If the heating coil of the kettle is shortened to half its original length and the supply voltage remains unchanged, then to boil the same amount of water will take

14.

Two light spheres suspended from silk threads

Two light conducting spheres are suspended from two silk threads as shown. If they are found to attract one another, which one of the following conclusions is/are correct ?

(1)They carry similar charges.

(2)They carry opposite charges.

(3)Only one of them is charged.

15.

Resistor network of five 2 ohm resistors between points A, B, C and D

The diagram shows a network of resistors, where the resistance of each resistor is $2\ \Omega$ . What are the equivalent resistances across $AB$ and $AD$ respectively ?

	$AB$	$AD$
	$1.67\ \Omega$	$1.00\ \Omega$
	$1.67\ \Omega$	$1.67\ \Omega$
	$1.67\ \Omega$	$3.67\ \Omega$
	$2.50\ \Omega$	$1.00\ \Omega$

16.

Circuit with resistors R1 and R2, ammeters A1 and A2, a 5000 ohm resistor between points A and B and a battery

In the circuit shown, ammeter $A_1$ reads $2$ mA and ammeter $A_2$ reads $8$ mA. What is the voltage across $AB$ ?

17.

2 V cell connected across a 4 ohm resistor and a 2 ohm resistor in parallel

In the circuit shown, what is the power dissipated in the $4\ \Omega$ resistor ?

18.

Which of the following statements concerning isotopes of an element is/are correct ?

(1)They have the same number of neutrons.

(2)They have the same chemical and physical properties.

(3)They have the same atomic number but different mass numbers.

19.

Two iron rods A and B suspended by strings with their lower ends inside a solenoid, current directions shown by arrows

The figure shows two iron rods $A$ and $B$ suspended by two light strings so that they are close together. Their lower ends are inside a solenoid. When a current flows through the solenoid, what will happen to $A$ and $B$ ?

	$A$	$B$
	moves to the left	moves to the right
	moves to the right	moves to the left
	moves to the right	moves to the right
	moves to the left	moves to the left

20.

Which of the following will be deflected by a magnetic field ?

(1)Electromagnetic waves

(2)A beam of electrons

(3)A beam of protons