物理 2005 年 DSE、CE 選擇題（第 2 頁）

11.

Grid showing an object, a lens and an image on the principal axis; scale 5 cm

An object is placed near a lens and an image is formed as shown. Which of the following statements are correct ?

(1)The height of the image is half that of the object.

(2)The lens is a concave lens.

(3)The focal length of the lens is

20

cm.

12.

Which of the following statements about sound waves are correct ?

(1)Sound waves are longitudinal waves.

(2)Sound waves are electromagnetic waves.

(3)Sound waves cannot travel in a vacuum.

13.

Straight water waves travelling towards a barrier inclined at 30 degrees

Straight water waves travel towards a barrier as shown above. Which of the following diagrams best shows the reflected wave pattern ?

Four diagrams A to D of reflected wave patterns

14.

A cork floats in water and a dropper is used to produce circular waves as shown in the diagram. Which of the following describes the motion of the cork when the waves pass through it ?

A dropper releasing drops onto water with a floating cork

15.

Which of the following shows the correct order of the relative positions of five electromagnetic waves in the electromagnetic spectrum, in the order of decreasing wavelength ?

16.

Two conducting spheres are hanging freely in air by insulating threads. In which of the following will the two spheres attract each other ? Note : 'N' denotes that the sphere is uncharged.

Three arrangements of two hanging spheres: (1) + and -, (2) + and N, (3) - and N

17.

Battery with three parallel branches: one bulb with ammeter A2, two bulbs in series with ammeter A1, and ammeter A3 in the main line

In the above circuit, the bulbs are identical. If the reading of $A_1$ is $1$ A, find the readings of ammeters $A_2$ and $A_3$ .

	Reading of $A_2$	Reading of $A_3$
	$0.5$ A	$1$ A
	$0.5$ A	$1.5$ A
	$2$ A	$2$ A
	$2$ A	$3$ A

18.

12 V battery with resistors R1 and R2 and switch S in series, voltmeter across R2 and the switch

In the above circuit, what is the reading of the voltmeter when switch $S$ is closed ?

19.

The following table shows three electrical appliances which Clara used in a certain month :

Appliance	Rating	Duration
air-conditioner	$220$ V, $1200$ W	$250$ hours
television	$220$ V, $250$ W	$80$ hours
computer	$220$ V, $150$ W	$60$ hours

Calculate the cost of electricity used. Note : $1$ kW h of electricity costs $\$0.86$ .

20.

If a $15$ A fuse is installed in the plug of an electric kettle of rating value ' $220$ V, $900$ W', which of the following descriptions is correct ?